diff --git a/AK/Base64.cpp b/AK/Base64.cpp
index f4a21a57a8..cd85868926 100644
--- a/AK/Base64.cpp
+++ b/AK/Base64.cpp
@@ -138,6 +138,22 @@ static ErrorOr<String> encode_base64_impl(ReadonlyBytes input, simdutf::base64_o
     return String { move(output) };
 }
 
+static Utf16String encode_base64_to_utf16_impl(ReadonlyBytes input, simdutf::base64_options options)
+{
+    if (input.is_empty())
+        return {};
+
+    return Utf16String::create_uninitialized_ascii(
+        simdutf::base64_length_from_binary(input.size(), options),
+        [&](Bytes buffer) {
+            simdutf::binary_to_base64(
+                reinterpret_cast<char const*>(input.data()),
+                input.size(),
+                reinterpret_cast<char*>(buffer.data()),
+                options);
+        });
+}
+
 ErrorOr<ByteBuffer> decode_base64(StringView input, LastChunkHandling last_chunk_handling)
 {
     return decode_base64_impl(input, last_chunk_handling, simdutf::base64_default);
@@ -186,4 +202,22 @@ ErrorOr<String> encode_base64url(ReadonlyBytes input, OmitPadding omit_padding)
     return encode_base64_impl(input, options);
 }
 
+ErrorOr<Utf16String> encode_base64_to_utf16(ReadonlyBytes input, OmitPadding omit_padding)
+{
+    auto options = omit_padding == OmitPadding::Yes
+        ? simdutf::base64_default_no_padding
+        : simdutf::base64_default;
+
+    return encode_base64_to_utf16_impl(input, options);
+}
+
+ErrorOr<Utf16String> encode_base64url_to_utf16(ReadonlyBytes input, OmitPadding omit_padding)
+{
+    auto options = omit_padding == OmitPadding::Yes
+        ? simdutf::base64_url
+        : simdutf::base64_url_with_padding;
+
+    return encode_base64_to_utf16_impl(input, options);
+}
+
 }
diff --git a/AK/Base64.h b/AK/Base64.h
index 63ef72a901..8aab8146ca 100644
--- a/AK/Base64.h
+++ b/AK/Base64.h
@@ -10,6 +10,7 @@
 #include <AK/Error.h>
 #include <AK/String.h>
 #include <AK/StringView.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 
 namespace AK {
@@ -45,6 +46,8 @@ enum class OmitPadding {
 
 ErrorOr<String> encode_base64(ReadonlyBytes, OmitPadding = OmitPadding::No);
 ErrorOr<String> encode_base64url(ReadonlyBytes, OmitPadding = OmitPadding::No);
+ErrorOr<Utf16String> encode_base64_to_utf16(ReadonlyBytes, OmitPadding = OmitPadding::No);
+ErrorOr<Utf16String> encode_base64url_to_utf16(ReadonlyBytes, OmitPadding = OmitPadding::No);
 
 }
 
@@ -52,5 +55,7 @@ ErrorOr<String> encode_base64url(ReadonlyBytes, OmitPadding = OmitPadding::No);
 using AK::decode_base64;
 using AK::decode_base64url;
 using AK::encode_base64;
+using AK::encode_base64_to_utf16;
 using AK::encode_base64url;
+using AK::encode_base64url_to_utf16;
 #endif
diff --git a/AK/Utf16String.h b/AK/Utf16String.h
index 26fed6dfaf..982c529670 100644
--- a/AK/Utf16String.h
+++ b/AK/Utf16String.h
@@ -239,6 +239,23 @@ public:
     static Utf16String from_string_builder(Badge<Utf16StringBuilder>, Utf16StringBuilder& builder);
     static ErrorOr<Utf16String> from_ipc_stream(Stream&, size_t length_in_code_units, bool is_ascii);
 
+    template<typename Callback>
+    static Utf16String create_uninitialized_ascii(size_t length_in_code_units, Callback callback)
+    {
+        if (length_in_code_units <= Detail::MAX_SHORT_STRING_BYTE_COUNT) {
+            Utf16String string;
+            string.m_value.short_ascii_string = Detail::ShortString::create_with_byte_count(length_in_code_units);
+
+            callback({ string.m_value.short_ascii_string.storage, length_in_code_units });
+            return string;
+        }
+
+        Bytes buffer;
+        Utf16String string { Detail::Utf16StringData::create_uninitialized_ascii(length_in_code_units, buffer) };
+        callback(buffer);
+        return string;
+    }
+
     constexpr Utf16String(Badge<Optional<Utf16String>>, nullptr_t)
         : Detail::Utf16StringBase(Badge<Utf16String> {}, nullptr)
     {
diff --git a/AK/Utf16StringData.cpp b/AK/Utf16StringData.cpp
index 70bce6e81a..c8733f8314 100644
--- a/AK/Utf16StringData.cpp
+++ b/AK/Utf16StringData.cpp
@@ -63,6 +63,15 @@ NonnullRefPtr<Utf16StringData> Utf16StringData::from_ascii(ReadonlyBytes ascii_s
     return string;
 }
 
+NonnullRefPtr<Utf16StringData> Utf16StringData::create_uninitialized_ascii(size_t length_in_code_units, Bytes& buffer)
+{
+    VERIFY_UTF16_LENGTH(length_in_code_units);
+
+    auto string = create_uninitialized(StorageType::ASCII, length_in_code_units);
+    buffer = { string->m_ascii_data, length_in_code_units };
+    return string;
+}
+
 NonnullRefPtr<Utf16StringData> Utf16StringData::from_utf8(StringView utf8_string, AllowASCIIStorage allow_ascii_storage)
 {
     RefPtr<Utf16StringData> string;
diff --git a/AK/Utf16StringData.h b/AK/Utf16StringData.h
index a84c83a197..dd54e2992d 100644
--- a/AK/Utf16StringData.h
+++ b/AK/Utf16StringData.h
@@ -15,6 +15,12 @@
 #include <AK/Utf16View.h>
 #include <AK/kmalloc.h>
 
+namespace AK {
+
+class Utf16String;
+
+}
+
 namespace AK::Detail {
 
 void did_destroy_utf16_fly_string_data(Badge<Detail::Utf16StringData>, Detail::Utf16StringData const&);
@@ -118,6 +124,8 @@ public:
     [[nodiscard]] ALWAYS_INLINE bool is_fly_string() const { return m_is_fly_string; }
 
 private:
+    friend class AK::Utf16String;
+
     ALWAYS_INLINE Utf16StringData(StorageType storage_type, size_t code_unit_length)
         : m_length_in_code_units(code_unit_length)
     {
@@ -126,6 +134,7 @@ private:
     }
 
     static NonnullRefPtr<Utf16StringData> create_uninitialized(StorageType storage_type, size_t code_unit_length);
+    static NonnullRefPtr<Utf16StringData> create_uninitialized_ascii(size_t length_in_code_units, Bytes& buffer);
 
     template<typename ViewType>
     static NonnullRefPtr<Utf16StringData> create_from_code_point_iterable(ViewType const&);
diff --git a/Libraries/LibCore/TimeZone.cpp b/Libraries/LibCore/TimeZone.cpp
index 536e0ec589..faf2cf4199 100644
--- a/Libraries/LibCore/TimeZone.cpp
+++ b/Libraries/LibCore/TimeZone.cpp
@@ -13,7 +13,8 @@ namespace Core::TimeZone {
 
 ErrorOr<void> set_current_time_zone(StringView time_zone)
 {
-    TRY(Unicode::set_current_time_zone(time_zone));
+    auto time_zone_utf16 = Utf16String::from_utf8(time_zone);
+    TRY(Unicode::set_current_time_zone(time_zone_utf16));
     TRY(Core::Environment::set("TZ"sv, time_zone, Core::Environment::Overwrite::Yes));
     tzset();
     return {};
@@ -21,7 +22,8 @@ ErrorOr<void> set_current_time_zone(StringView time_zone)
 
 String current_time_zone()
 {
-    return Unicode::current_time_zone();
+    auto time_zone = Unicode::current_time_zone();
+    return time_zone.utf16_view().to_utf8_but_should_be_ported_to_utf16();
 }
 
 }
diff --git a/Libraries/LibCrypto/BigFraction/BigFraction.cpp b/Libraries/LibCrypto/BigFraction/BigFraction.cpp
index 4e7cb05269..85fd1c0fc2 100644
--- a/Libraries/LibCrypto/BigFraction/BigFraction.cpp
+++ b/Libraries/LibCrypto/BigFraction/BigFraction.cpp
@@ -5,9 +5,9 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/ByteString.h>
 #include <AK/Math.h>
 #include <AK/StringBuilder.h>
+#include <AK/Utf16StringBuilder.h>
 #include <LibCrypto/BigFraction/BigFraction.h>
 #include <LibCrypto/BigInt/UnsignedBigInteger.h>
 
@@ -233,11 +233,11 @@ void BigFraction::reduce()
     m_denominator = denominator_divide.quotient;
 }
 
-String BigFraction::to_string(unsigned rounding_threshold) const
+Utf16String BigFraction::to_utf16_string(unsigned rounding_threshold) const
 {
-    StringBuilder builder;
+    Utf16StringBuilder builder;
     if (m_numerator.is_negative() && m_numerator != "0"_bigint)
-        builder.append('-');
+        builder.append_ascii('-');
 
     auto const number_of_digits = [](auto integer) {
         unsigned size = 1;
@@ -256,43 +256,48 @@ String BigFraction::to_string(unsigned rounding_threshold) const
     auto const rounded_fraction = rounded(rounding_threshold);
 
     // We take the unsigned value as we already manage the '-'
-    auto const full_value = MUST(rounded_fraction.m_numerator.unsigned_value().to_base(10)).to_byte_string();
-    int split = full_value.length() - (number_of_digits(rounded_fraction.m_denominator) - 1);
+    auto const full_value = MUST(rounded_fraction.m_numerator.unsigned_value().to_base_utf16(10));
+    int split = full_value.length_in_code_units() - (number_of_digits(rounded_fraction.m_denominator) - 1);
 
     if (split < 0)
         split = 0;
 
-    auto const remove_trailing_zeros = [](StringView value) -> StringView {
-        auto n = value.length();
+    auto const remove_trailing_zeros = [](Utf16View value) -> Utf16View {
+        auto n = value.length_in_code_units();
         VERIFY(n > 0);
-        while (n > 0 && value.characters_without_null_termination()[n - 1] == '0')
+        while (n > 0 && value.code_unit_at(n - 1) == '0')
             --n;
-        return { value.characters_without_null_termination(), n };
+        return value.substring_view(0, n);
     };
 
-    auto const raw_fractional_value = full_value.substring(split, full_value.length() - split);
+    auto const raw_fractional_value = full_value.substring_view(split, full_value.length_in_code_units() - split);
 
-    auto const integer_value = split == 0 ? "0"sv : full_value.substring_view(0, split);
-    auto const fractional_value = rounding_threshold == 0 ? "0"sv : remove_trailing_zeros(raw_fractional_value);
+    Utf16View integer_value = "0"sv;
+    if (split != 0)
+        integer_value = full_value.substring_view(0, split);
+
+    Utf16View fractional_value = "0"sv;
+    if (rounding_threshold != 0)
+        fractional_value = remove_trailing_zeros(raw_fractional_value);
 
     builder.append(integer_value);
 
-    bool const has_decimal_part = fractional_value.length() > 0 && fractional_value != "0";
+    bool const has_decimal_part = fractional_value.length_in_code_units() > 0 && fractional_value != "0"sv;
 
     if (has_decimal_part) {
-        builder.append('.');
+        builder.append_ascii('.');
 
-        auto number_pre_zeros = number_of_digits(rounded_fraction.m_denominator) - full_value.length() - 1;
-        if (number_pre_zeros > rounding_threshold || fractional_value == "0")
+        auto number_pre_zeros = number_of_digits(rounded_fraction.m_denominator) - full_value.length_in_code_units() - 1;
+        if (number_pre_zeros > rounding_threshold || fractional_value == "0"sv)
             number_pre_zeros = 0;
 
-        builder.append_repeated('0', number_pre_zeros);
+        builder.append_repeated_ascii('0', number_pre_zeros);
 
-        if (fractional_value != "0")
+        if (fractional_value != "0"sv)
             builder.append(fractional_value);
     }
 
-    return MUST(builder.to_string());
+    return builder.to_string();
 }
 
 BigFraction BigFraction::sqrt() const
diff --git a/Libraries/LibCrypto/BigFraction/BigFraction.h b/Libraries/LibCrypto/BigFraction/BigFraction.h
index e148cb90d3..eb800c058f 100644
--- a/Libraries/LibCrypto/BigFraction/BigFraction.h
+++ b/Libraries/LibCrypto/BigFraction/BigFraction.h
@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include <AK/Utf16String.h>
 #include <LibCrypto/BigInt/SignedBigInteger.h>
 
 namespace Crypto {
@@ -55,7 +56,7 @@ public:
     //      - m_denominator = 10000
     BigFraction rounded(unsigned rounding_threshold) const;
 
-    String to_string(unsigned rounding_threshold) const;
+    Utf16String to_utf16_string(unsigned rounding_threshold) const;
     double to_double() const;
 
     Crypto::SignedBigInteger const& numerator() const& { return m_numerator; }
diff --git a/Libraries/LibCrypto/BigInt/SignedBigInteger.cpp b/Libraries/LibCrypto/BigInt/SignedBigInteger.cpp
index 9da6344245..e7444895e8 100644
--- a/Libraries/LibCrypto/BigInt/SignedBigInteger.cpp
+++ b/Libraries/LibCrypto/BigInt/SignedBigInteger.cpp
@@ -9,6 +9,8 @@
 #include <math.h>
 #include <tommath.h>
 
+#include <AK/StringBuilder.h>
+#include <AK/Utf16StringBuilder.h>
 #include <LibCrypto/BigInt/SignedBigInteger.h>
 #include <LibCrypto/BigInt/Tommath.h>
 
@@ -170,6 +172,28 @@ ErrorOr<String> SignedBigInteger::to_base(u16 N) const
     return StringView(buffer.bytes().slice(0, written - 1)).to_ascii_lowercase_string();
 }
 
+ErrorOr<Utf16String> SignedBigInteger::to_base_utf16(u16 N) const
+{
+    VERIFY(N <= 36);
+    if (is_zero())
+        return "0"_utf16;
+
+    int size = 0;
+    MP_MUST(mp_radix_size(&m_mp, N, &size));
+    auto buffer = TRY(ByteBuffer::create_zeroed(size));
+
+    size_t written = 0;
+    MP_MUST(mp_to_radix(&m_mp, reinterpret_cast<char*>(buffer.data()), size, &written, N));
+
+    Utf16StringBuilder builder(written - 1);
+    for (auto character : buffer.bytes().slice(0, written - 1)) {
+        if (character >= 'A' && character <= 'Z')
+            character += 'a' - 'A';
+        builder.append_code_unit(character);
+    }
+    return builder.to_string();
+}
+
 i64 SignedBigInteger::to_i64() const
 {
     return mp_get_i64(&m_mp);
diff --git a/Libraries/LibCrypto/BigInt/SignedBigInteger.h b/Libraries/LibCrypto/BigInt/SignedBigInteger.h
index bf30198c65..1f94097140 100644
--- a/Libraries/LibCrypto/BigInt/SignedBigInteger.h
+++ b/Libraries/LibCrypto/BigInt/SignedBigInteger.h
@@ -8,6 +8,7 @@
 
 #pragma once
 
+#include <AK/Utf16String.h>
 #include <LibCrypto/BigInt/UnsignedBigInteger.h>
 
 namespace Crypto {
@@ -44,6 +45,7 @@ public:
     [[nodiscard]] static ErrorOr<SignedBigInteger> from_base(u16 N, StringView str);
     [[nodiscard]] static ErrorOr<SignedBigInteger> from_base(u16 N, Utf16View str);
     [[nodiscard]] ErrorOr<String> to_base(u16 N) const;
+    [[nodiscard]] ErrorOr<Utf16String> to_base_utf16(u16 N) const;
 
     [[nodiscard]] i64 to_i64() const;
     [[nodiscard]] u64 to_u64() const;
diff --git a/Libraries/LibCrypto/BigInt/UnsignedBigInteger.cpp b/Libraries/LibCrypto/BigInt/UnsignedBigInteger.cpp
index 2ad5676f0e..b9af8bd175 100644
--- a/Libraries/LibCrypto/BigInt/UnsignedBigInteger.cpp
+++ b/Libraries/LibCrypto/BigInt/UnsignedBigInteger.cpp
@@ -11,6 +11,8 @@
 
 #include <AK/BuiltinWrappers.h>
 #include <AK/FloatingPoint.h>
+#include <AK/StringBuilder.h>
+#include <AK/Utf16StringBuilder.h>
 #include <LibCrypto/BigInt/Tommath.h>
 #include <LibCrypto/BigInt/UnsignedBigInteger.h>
 
@@ -172,6 +174,28 @@ ErrorOr<String> UnsignedBigInteger::to_base(u16 N) const
     return StringView(buffer.bytes().slice(0, written - 1)).to_ascii_lowercase_string();
 }
 
+ErrorOr<Utf16String> UnsignedBigInteger::to_base_utf16(u16 N) const
+{
+    VERIFY(N <= 36);
+    if (is_zero())
+        return "0"_utf16;
+
+    int size = 0;
+    MP_MUST(mp_radix_size(&m_mp, N, &size));
+    auto buffer = TRY(ByteBuffer::create_zeroed(size));
+
+    size_t written = 0;
+    MP_MUST(mp_to_radix(&m_mp, reinterpret_cast<char*>(buffer.data()), size, &written, N));
+
+    Utf16StringBuilder builder(written - 1);
+    for (auto character : buffer.bytes().slice(0, written - 1)) {
+        if (character >= 'A' && character <= 'Z')
+            character += 'a' - 'A';
+        builder.append_code_unit(character);
+    }
+    return builder.to_string();
+}
+
 size_t UnsignedBigInteger::count_digits_in_base(u16 base) const
 {
     VERIFY(base <= 36);
diff --git a/Libraries/LibCrypto/BigInt/UnsignedBigInteger.h b/Libraries/LibCrypto/BigInt/UnsignedBigInteger.h
index 1d6ca5fb7d..023cb276fb 100644
--- a/Libraries/LibCrypto/BigInt/UnsignedBigInteger.h
+++ b/Libraries/LibCrypto/BigInt/UnsignedBigInteger.h
@@ -10,6 +10,7 @@
 #pragma once
 
 #include <AK/String.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 #include <LibCrypto/BigInt/TommathForward.h>
 
@@ -47,6 +48,7 @@ public:
     [[nodiscard]] static ErrorOr<UnsignedBigInteger> from_base(u16 N, StringView str);
     [[nodiscard]] static ErrorOr<UnsignedBigInteger> from_base(u16 N, Utf16View str);
     [[nodiscard]] ErrorOr<String> to_base(u16 N) const;
+    [[nodiscard]] ErrorOr<Utf16String> to_base_utf16(u16 N) const;
 
     [[nodiscard]] size_t count_digits_in_base(u16 base) const;
 
diff --git a/Libraries/LibJS/Bytecode/AsmInterpreter/AsmSlowPaths.cpp b/Libraries/LibJS/Bytecode/AsmInterpreter/AsmSlowPaths.cpp
index 7cb03aa32d..000fa221de 100644
--- a/Libraries/LibJS/Bytecode/AsmInterpreter/AsmSlowPaths.cpp
+++ b/Libraries/LibJS/Bytecode/AsmInterpreter/AsmSlowPaths.cpp
@@ -245,7 +245,7 @@ static ThrowCompletionOr<void> asm_create_variable(VM& vm, Utf16FlyString const&
         // Note: This is papering over an issue where "FunctionDeclarationInstantiation" creates these bindings for us.
         //       Instead of crashing in there, we'll just raise an exception here.
         if (TRY(vm.lexical_environment()->has_binding(name))) [[unlikely]]
-            return vm.throw_completion<InternalError>(TRY_OR_THROW_OOM(vm, String::formatted("Lexical environment already has binding '{}'", name)));
+            return vm.throw_completion<InternalError>(Utf16String::formatted("Lexical environment already has binding '{}'", name));
 
         if (is_immutable)
             return vm.lexical_environment()->create_immutable_binding(vm, name, is_strict);
@@ -2344,7 +2344,7 @@ i64 asm_slow_path_dynamic_typeof_binding(VM* vm, u32 pc, Op::DynamicTypeofBindin
 
     auto reference = ASM_TRY(*vm, pc, vm->resolve_binding(vm->get_identifier(instruction->identifier()), instruction->strict()));
     if (reference.is_unresolvable()) {
-        vm->set(instruction->dst(), PrimitiveString::create(*vm, "undefined"_string));
+        vm->set(instruction->dst(), PrimitiveString::create(*vm, "undefined"_utf16_fly_string));
         return static_cast<i64>(pc + sizeof(Op::DynamicTypeofBinding));
     }
 
diff --git a/Libraries/LibJS/Bytecode/Executable.cpp b/Libraries/LibJS/Bytecode/Executable.cpp
index fa509acc4a..12a64e606d 100644
--- a/Libraries/LibJS/Bytecode/Executable.cpp
+++ b/Libraries/LibJS/Bytecode/Executable.cpp
@@ -409,7 +409,7 @@ static void dump_metadata(StringBuilder& output, Executable const& executable)
             else if (value.is_double())
                 output.appendff("Double({})", value.as_double());
             else if (value.is_bigint())
-                output.appendff("BigInt({})", MUST(value.as_bigint().to_string()));
+                output.appendff("BigInt({})", value.as_bigint().to_utf16_string());
             else if (value.is_string())
                 output.appendff("String(\"{}\")", value.as_string().utf16_string_view());
             else if (value.is_undefined())
diff --git a/Libraries/LibJS/Console.cpp b/Libraries/LibJS/Console.cpp
index c601b958fd..790b63a065 100644
--- a/Libraries/LibJS/Console.cpp
+++ b/Libraries/LibJS/Console.cpp
@@ -52,7 +52,7 @@ ThrowCompletionOr<Value> Console::assert_()
         return js_undefined();
 
     // 2. Let message be a string without any formatting specifiers indicating generically an assertion failure (such as "Assertion failed").
-    auto message = PrimitiveString::create(vm, "Assertion failed"_string);
+    auto message = PrimitiveString::create(vm, "Assertion failed"_utf16_fly_string);
 
     // NOTE: Assemble `data` from the function arguments.
     GC::RootVector<Value> data;
@@ -362,7 +362,7 @@ ThrowCompletionOr<Value> Console::trace()
         Console::TraceFrame frame;
 
         auto function_name = (context && context->function) ? context->function->name_for_call_stack() : ""_utf16;
-        frame.function_name = function_name.is_empty() ? "<anonymous>"_string : function_name.to_utf8();
+        frame.function_name = function_name.is_empty() ? "<anonymous>"_utf16 : function_name;
 
         if (element.source_range.has_value()) {
             auto const& source_range = *element.source_range;
@@ -963,19 +963,17 @@ ThrowCompletionOr<GC::RootVector<Value>> ConsoleClient::formatter(GC::RootVector
 
 ThrowCompletionOr<Utf16String> ConsoleClient::generically_format_values(GC::RootVector<Value> const& values)
 {
-    AllocatingMemoryStream stream;
     auto& vm = m_console->realm().vm();
-    PrintContext ctx { vm, stream, true };
+    Utf16StringBuilder builder;
+    PrintContext ctx { .vm = vm, .builder = &builder, .strip_ansi = true };
     bool first = true;
     for (auto const& value : values) {
         if (!first)
-            TRY_OR_THROW_OOM(vm, stream.write_until_depleted(" "sv.bytes()));
+            builder.append_ascii(' ');
         TRY_OR_THROW_OOM(vm, JS::print(value, ctx));
         first = false;
     }
-    // FIXME: Is it possible we could end up serializing objects to invalid UTF-8?
-    auto output = TRY_OR_THROW_OOM(vm, String::from_stream(stream, stream.used_buffer_size()));
-    return Utf16String::from_utf8(output);
+    return builder.to_string();
 }
 
 }
diff --git a/Libraries/LibJS/Console.h b/Libraries/LibJS/Console.h
index 4e9dec68c0..bfbacb0012 100644
--- a/Libraries/LibJS/Console.h
+++ b/Libraries/LibJS/Console.h
@@ -58,7 +58,7 @@ public:
     };
 
     struct TraceFrame {
-        String function_name;
+        Utf16String function_name;
         Optional<String> source_file;
         Optional<size_t> line;
         Optional<size_t> column;
diff --git a/Libraries/LibJS/Contrib/Test262/262Object.cpp b/Libraries/LibJS/Contrib/Test262/262Object.cpp
index c7cf4e87cf..37cf535b8a 100644
--- a/Libraries/LibJS/Contrib/Test262/262Object.cpp
+++ b/Libraries/LibJS/Contrib/Test262/262Object.cpp
@@ -108,7 +108,7 @@ JS_DEFINE_NATIVE_FUNCTION($262Object::eval_script)
         auto& error = script_or_error.error()[0];
 
         // b. Return Completion { [[Type]]: throw, [[Value]]: error, [[Target]]: empty }.
-        return vm.throw_completion<SyntaxError>(error.to_string());
+        return vm.throw_completion<SyntaxError>(error.to_utf16_string());
     }
 
     // 5. Let status be ScriptEvaluation(s).
diff --git a/Libraries/LibJS/ParserError.cpp b/Libraries/LibJS/ParserError.cpp
index cdc3f0816d..d8ea8b9797 100644
--- a/Libraries/LibJS/ParserError.cpp
+++ b/Libraries/LibJS/ParserError.cpp
@@ -13,18 +13,18 @@
 
 namespace JS {
 
-String ParserError::to_string() const
+Utf16String ParserError::to_utf16_string() const
 {
     if (!position.has_value())
         return message;
-    return MUST(String::formatted("{} (line: {}, column: {})", message, position.value().line, position.value().column));
+    return Utf16String::formatted("{} (line: {}, column: {})", message, position.value().line, position.value().column);
 }
 
 ByteString ParserError::to_byte_string() const
 {
     if (!position.has_value())
         return message.to_byte_string();
-    return ByteString::formatted("{} (line: {}, column: {})", message, position.value().line, position.value().column);
+    return Utf16String::formatted("{} (line: {}, column: {})", message, position.value().line, position.value().column).to_byte_string();
 }
 
 ByteString ParserError::source_location_hint(Utf16View const& source, char spacer, char indicator) const
diff --git a/Libraries/LibJS/ParserError.h b/Libraries/LibJS/ParserError.h
index d7b2c87e05..8b08933245 100644
--- a/Libraries/LibJS/ParserError.h
+++ b/Libraries/LibJS/ParserError.h
@@ -10,17 +10,17 @@
 #include <AK/ByteString.h>
 #include <AK/Error.h>
 #include <AK/Optional.h>
-#include <AK/String.h>
+#include <AK/Utf16String.h>
 #include <LibJS/Export.h>
 #include <LibJS/SourceRange.h>
 
 namespace JS {
 
 struct JS_API ParserError {
-    String message;
+    Utf16String message;
     Optional<Position> position;
 
-    String to_string() const;
+    Utf16String to_utf16_string() const;
     ByteString to_byte_string() const;
     ByteString source_location_hint(Utf16View const& source, char spacer = ' ', char indicator = '^') const;
 };
diff --git a/Libraries/LibJS/Print.cpp b/Libraries/LibJS/Print.cpp
index e5e5c317a5..1b2e1df4f3 100644
--- a/Libraries/LibJS/Print.cpp
+++ b/Libraries/LibJS/Print.cpp
@@ -8,6 +8,7 @@
 
 #include <AK/Concepts.h>
 #include <AK/Stream.h>
+#include <AK/StringBuilder.h>
 #include <AK/Utf16StringBuilder.h>
 #include <LibJS/Print.h>
 #include <LibJS/Runtime/Array.h>
@@ -140,9 +141,21 @@ ErrorOr<void> js_out(JS::PrintContext& print_context, CheckedFormatString<Args..
 {
     if (print_context.strip_ansi) {
         auto format_string_without_ansi = TRY(strip_ansi(format_string.view()));
-        TRY(print_context.stream.write_formatted(format_string_without_ansi, args...));
+        if (print_context.builder) {
+            AK::VariadicFormatParams<AK::AllowDebugOnlyFormatters::No, Args...> variadic_format_parameters { args... };
+            TRY(vformat(*print_context.builder, format_string_without_ansi.bytes_as_string_view(), variadic_format_parameters));
+        } else {
+            VERIFY(print_context.stream);
+            TRY(print_context.stream->write_formatted(format_string_without_ansi, args...));
+        }
     } else {
-        TRY(print_context.stream.write_formatted(format_string.view(), args...));
+        if (print_context.builder) {
+            AK::VariadicFormatParams<AK::AllowDebugOnlyFormatters::No, Args...> variadic_format_parameters { args... };
+            TRY(vformat(*print_context.builder, format_string.view(), variadic_format_parameters));
+        } else {
+            VERIFY(print_context.stream);
+            TRY(print_context.stream->write_formatted(format_string.view(), args...));
+        }
     }
 
     return {};
@@ -684,7 +697,7 @@ ErrorOr<void> print_intl_date_time_format(JS::PrintContext& print_context, JS::I
                 return JS::throw_completion(JS::js_null());
         } else {
             auto name = Unicode::calendar_pattern_style_to_string(*option);
-            if (print_value(print_context, JS::PrimitiveString::create(date_time_format.vm(), name), seen_objects).is_error())
+            if (print_value(print_context, JS::PrimitiveString::create(date_time_format.vm(), move(name)), seen_objects).is_error())
                 return JS::throw_completion(JS::js_null());
         }
 
@@ -788,10 +801,10 @@ ErrorOr<void> print_intl_duration_format(JS::PrintContext& print_context, JS::In
         auto display = JS::Intl::DurationFormat::display_to_string(options.display);
 
         TRY(js_out(print_context, "\n  {}: ", style_name));
-        TRY(print_value(print_context, JS::PrimitiveString::create(duration_format.vm(), style), seen_objects));
+        TRY(print_value(print_context, JS::PrimitiveString::create(duration_format.vm(), move(style)), seen_objects));
 
         TRY(js_out(print_context, "\n  {}: ", display_name));
-        TRY(print_value(print_context, JS::PrimitiveString::create(duration_format.vm(), display), seen_objects));
+        TRY(print_value(print_context, JS::PrimitiveString::create(duration_format.vm(), move(display)), seen_objects));
 
         return {};
     };
diff --git a/Libraries/LibJS/Print.h b/Libraries/LibJS/Print.h
index f384d05c94..6de15dcce3 100644
--- a/Libraries/LibJS/Print.h
+++ b/Libraries/LibJS/Print.h
@@ -12,11 +12,19 @@
 #include <LibJS/Export.h>
 #include <LibJS/Runtime/Value.h>
 
+namespace AK {
+
+class Stream;
+class Utf16StringBuilder;
+
+}
+
 namespace JS {
 
 struct PrintContext {
     JS::VM& vm;
-    Stream& stream;
+    AK::Stream* stream { nullptr };
+    AK::Utf16StringBuilder* builder { nullptr };
     bool strip_ansi { false };
     bool raw_strings { false };
 };
diff --git a/Libraries/LibJS/Runtime/AbstractOperations.cpp b/Libraries/LibJS/Runtime/AbstractOperations.cpp
index b6186fde88..405b8c87ec 100644
--- a/Libraries/LibJS/Runtime/AbstractOperations.cpp
+++ b/Libraries/LibJS/Runtime/AbstractOperations.cpp
@@ -702,7 +702,7 @@ ThrowCompletionOr<Value> perform_eval(VM& vm, Value x, CallerMode strict_caller,
 
     auto rust_compilation = RustIntegration::compile_eval(*code_string, vm, strict_caller, in_function, in_method, in_derived_constructor, in_class_field_initializer);
     if (!rust_compilation.has_value())
-        return vm.throw_completion<SyntaxError>("Failed to compile eval code"_string);
+        return vm.throw_completion<SyntaxError>("Failed to compile eval code"_utf16);
     if (rust_compilation->is_error())
         return vm.throw_completion<SyntaxError>(rust_compilation->release_error());
     auto& eval_result = rust_compilation->value();
@@ -1277,7 +1277,7 @@ CanonicalIndex canonical_numeric_index_string(PropertyKey const& property_key, C
 
     // FIXME: We return 0 instead of n but it might not observable?
     // 3. If SameValue(! ToString(n), argument) is true, return n.
-    if (number_to_string(*maybe_double) == argument)
+    if (number_to_utf16_string(*maybe_double) == argument)
         return CanonicalIndex(CanonicalIndex::Type::Numeric, 0);
 
     // 4. Return undefined.
@@ -1934,7 +1934,7 @@ ThrowCompletionOr<Value> get_option(VM& vm, Object const& options, PropertyKey c
             [](Empty) -> Value { return js_undefined(); },
             [](bool default_) -> Value { return Value { default_ }; },
             [](double default_) -> Value { return Value { default_ }; },
-            [&](StringView default_) -> Value { return PrimitiveString::create(vm, default_); });
+            [&](Utf16View default_) -> Value { return PrimitiveString::create(vm, default_); });
     }
 
     // 3. If type is BOOLEAN, then
@@ -1960,8 +1960,6 @@ ThrowCompletionOr<Value> get_option(VM& vm, Object const& options, PropertyKey c
         auto it = find_if(values.begin(), values.end(), [&](auto allowed_value) { return value_string == allowed_value; });
         if (it == values.end())
             return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, value_string, property.as_string());
-
-        value = PrimitiveString::create(vm, *it);
     }
 
     // 6. Return value.
@@ -1975,7 +1973,8 @@ ThrowCompletionOr<RoundingMode> get_rounding_mode_option(VM& vm, Object const& o
     static constexpr auto allowed_strings = to_array({ "ceil"sv, "floor"sv, "expand"sv, "trunc"sv, "halfCeil"sv, "halfFloor"sv, "halfExpand"sv, "halfTrunc"sv, "halfEven"sv });
 
     // 2. Let stringFallback be the value from the "String Identifier" column of the row with fallback in its "Rounding Mode" column.
-    auto string_fallback = allowed_strings[to_underlying(fallback)];
+    static constexpr auto utf16_allowed_strings = to_array({ u"ceil"sv, u"floor"sv, u"expand"sv, u"trunc"sv, u"halfCeil"sv, u"halfFloor"sv, u"halfExpand"sv, u"halfTrunc"sv, u"halfEven"sv });
+    auto string_fallback = utf16_allowed_strings[to_underlying(fallback)];
 
     // 3. Let stringValue be ? GetOption(options, "roundingMode", STRING, allowedStrings, stringFallback).
     auto string_value = TRY(get_option(vm, options, vm.names.roundingMode, OptionType::String, allowed_strings, string_fallback));
diff --git a/Libraries/LibJS/Runtime/AbstractOperations.h b/Libraries/LibJS/Runtime/AbstractOperations.h
index 07dd041e18..3647f82cc7 100644
--- a/Libraries/LibJS/Runtime/AbstractOperations.h
+++ b/Libraries/LibJS/Runtime/AbstractOperations.h
@@ -11,6 +11,7 @@
 #include <AK/HashTable.h>
 #include <AK/NonnullRefPtr.h>
 #include <AK/Utf16FlyString.h>
+#include <AK/Utf16View.h>
 #include <LibCrypto/Forward.h>
 #include <LibGC/RootVector.h>
 #include <LibJS/Export.h>
@@ -375,7 +376,7 @@ enum class OptionType {
 };
 
 struct Required { };
-using OptionDefault = Variant<Required, Empty, bool, StringView, double>;
+using OptionDefault = Variant<Required, Empty, bool, Utf16View, double>;
 
 ThrowCompletionOr<GC::Ref<Object>> get_options_object(VM&, Value options);
 ThrowCompletionOr<Value> get_option(VM&, Object const& options, PropertyKey const& property, OptionType type, ReadonlySpan<StringView> values, OptionDefault const&);
diff --git a/Libraries/LibJS/Runtime/AggregateErrorPrototype.cpp b/Libraries/LibJS/Runtime/AggregateErrorPrototype.cpp
index 3a7451a61f..895e8b4c0c 100644
--- a/Libraries/LibJS/Runtime/AggregateErrorPrototype.cpp
+++ b/Libraries/LibJS/Runtime/AggregateErrorPrototype.cpp
@@ -22,8 +22,8 @@ void AggregateErrorPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
     Base::initialize(realm);
     u8 attr = Attribute::Writable | Attribute::Configurable;
-    define_direct_property(vm.names.name, PrimitiveString::create(vm, "AggregateError"_string), attr);
-    define_direct_property(vm.names.message, PrimitiveString::create(vm, String {}), attr);
+    define_direct_property(vm.names.name, PrimitiveString::create(vm, "AggregateError"_utf16_fly_string), attr);
+    define_direct_property(vm.names.message, PrimitiveString::create(vm, Utf16String {}), attr);
 }
 
 }
diff --git a/Libraries/LibJS/Runtime/ArrayIteratorPrototype.cpp b/Libraries/LibJS/Runtime/ArrayIteratorPrototype.cpp
index b974d51e01..c02ef2a5e7 100644
--- a/Libraries/LibJS/Runtime/ArrayIteratorPrototype.cpp
+++ b/Libraries/LibJS/Runtime/ArrayIteratorPrototype.cpp
@@ -29,7 +29,7 @@ void ArrayIteratorPrototype::initialize(Realm& realm)
     define_native_function(realm, vm.names.next, next, 0, Attribute::Configurable | Attribute::Writable, Bytecode::Builtin::ArrayIteratorPrototypeNext);
 
     // 23.1.5.2.2 %ArrayIteratorPrototype% [ @@toStringTag ], https://tc39.es/ecma262/#sec-%arrayiteratorprototype%-@@tostringtag
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Array Iterator"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Array Iterator"_utf16_fly_string), Attribute::Configurable);
 }
 
 // 23.1.5.2.1 %ArrayIteratorPrototype%.next ( ), https://tc39.es/ecma262/#sec-%arrayiteratorprototype%.next
diff --git a/Libraries/LibJS/Runtime/ArrayPrototype.cpp b/Libraries/LibJS/Runtime/ArrayPrototype.cpp
index 3135f044a3..31266f4b0b 100644
--- a/Libraries/LibJS/Runtime/ArrayPrototype.cpp
+++ b/Libraries/LibJS/Runtime/ArrayPrototype.cpp
@@ -924,7 +924,7 @@ JS_DEFINE_NATIVE_FUNCTION(ArrayPrototype::join)
     // FWIW: engine262, a "100% spec compliant" ECMA-262 impl, aborts with "too much recursion".
     // Same applies to Array.prototype.toLocaleString().
     if (array_join_seen_objects().contains(this_object))
-        return PrimitiveString::create(vm, String {});
+        return PrimitiveString::create(vm, Utf16String {});
     array_join_seen_objects().set(this_object);
     ArmedScopeGuard unsee_object_guard = [&] {
         array_join_seen_objects().remove(this_object);
@@ -1809,7 +1809,7 @@ JS_DEFINE_NATIVE_FUNCTION(ArrayPrototype::to_locale_string)
     auto this_object = TRY(vm.this_value().to_object(vm));
 
     if (array_join_seen_objects().contains(this_object))
-        return PrimitiveString::create(vm, String {});
+        return PrimitiveString::create(vm, Utf16String {});
     array_join_seen_objects().set(this_object);
     ArmedScopeGuard unsee_object_guard = [&] {
         array_join_seen_objects().remove(this_object);
diff --git a/Libraries/LibJS/Runtime/AsyncGeneratorPrototype.cpp b/Libraries/LibJS/Runtime/AsyncGeneratorPrototype.cpp
index f914f0ed59..0fa2cf7698 100644
--- a/Libraries/LibJS/Runtime/AsyncGeneratorPrototype.cpp
+++ b/Libraries/LibJS/Runtime/AsyncGeneratorPrototype.cpp
@@ -30,7 +30,7 @@ void AsyncGeneratorPrototype::initialize(Realm& realm)
     define_native_function(realm, vm.names.throw_, throw_, 1, attr);
 
     // 27.6.1.5 AsyncGenerator.prototype [ @@toStringTag ], https://tc39.es/ecma262/#sec-asyncgenerator-prototype-tostringtag
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "AsyncGenerator"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "AsyncGenerator"_utf16_fly_string), Attribute::Configurable);
 }
 
 // 27.6.3.3 AsyncGeneratorValidate ( generator, generatorBrand ), https://tc39.es/ecma262/#sec-asyncgeneratorvalidate
diff --git a/Libraries/LibJS/Runtime/AtomicsObject.cpp b/Libraries/LibJS/Runtime/AtomicsObject.cpp
index a08e135805..9d86282834 100644
--- a/Libraries/LibJS/Runtime/AtomicsObject.cpp
+++ b/Libraries/LibJS/Runtime/AtomicsObject.cpp
@@ -248,7 +248,7 @@ void AtomicsObject::initialize(Realm& realm)
     define_native_function(realm, vm.names.xor_, xor_, 3, attr);
 
     // 25.4.17 Atomics [ @@toStringTag ], https://tc39.es/ecma262/#sec-atomics-@@tostringtag
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Atomics"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Atomics"_utf16_fly_string), Attribute::Configurable);
 }
 
 // 25.4.4 Atomics.add ( typedArray, index, value ), https://tc39.es/ecma262/#sec-atomics.add
diff --git a/Libraries/LibJS/Runtime/BigInt.cpp b/Libraries/LibJS/Runtime/BigInt.cpp
index 9467c6f574..83d1d1dbe9 100644
--- a/Libraries/LibJS/Runtime/BigInt.cpp
+++ b/Libraries/LibJS/Runtime/BigInt.cpp
@@ -23,14 +23,9 @@ BigInt::BigInt(Crypto::SignedBigInteger big_integer)
 {
 }
 
-ErrorOr<String> BigInt::to_string() const
-{
-    return String::formatted("{}n", TRY(m_big_integer.to_base(10)));
-}
-
 Utf16String BigInt::to_utf16_string() const
 {
-    return Utf16String::formatted("{}n", MUST(m_big_integer.to_base(10)));
+    return Utf16String::formatted("{}n", MUST(m_big_integer.to_base_utf16(10)));
 }
 
 size_t BigInt::external_memory_size() const
diff --git a/Libraries/LibJS/Runtime/BigInt.h b/Libraries/LibJS/Runtime/BigInt.h
index 47181b2b27..3db850bb75 100644
--- a/Libraries/LibJS/Runtime/BigInt.h
+++ b/Libraries/LibJS/Runtime/BigInt.h
@@ -27,7 +27,6 @@ public:
 
     Crypto::SignedBigInteger const& big_integer() const { return m_big_integer; }
 
-    ErrorOr<String> to_string() const;
     Utf16String to_utf16_string() const;
 
 private:
diff --git a/Libraries/LibJS/Runtime/BigIntPrototype.cpp b/Libraries/LibJS/Runtime/BigIntPrototype.cpp
index 88595db5cc..8e40c2de25 100644
--- a/Libraries/LibJS/Runtime/BigIntPrototype.cpp
+++ b/Libraries/LibJS/Runtime/BigIntPrototype.cpp
@@ -74,7 +74,7 @@ JS_DEFINE_NATIVE_FUNCTION(BigIntPrototype::to_string)
     }
 
     // 5. Return BigInt::toString(x, radixMV).
-    return PrimitiveString::create(vm, TRY_OR_THROW_OOM(vm, bigint->big_integer().to_base(radix)));
+    return PrimitiveString::create(vm, TRY_OR_THROW_OOM(vm, bigint->big_integer().to_base_utf16(radix)));
 }
 
 // 21.2.3.2 BigInt.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] ), https://tc39.es/ecma262/#sec-bigint.prototype.tolocalestring
diff --git a/Libraries/LibJS/Runtime/BooleanPrototype.cpp b/Libraries/LibJS/Runtime/BooleanPrototype.cpp
index 8d8a5713d5..68e84dc242 100644
--- a/Libraries/LibJS/Runtime/BooleanPrototype.cpp
+++ b/Libraries/LibJS/Runtime/BooleanPrototype.cpp
@@ -55,7 +55,7 @@ JS_DEFINE_NATIVE_FUNCTION(BooleanPrototype::to_string)
     auto b = TRY(this_boolean_value(vm, vm.this_value()));
 
     // 2. If b is true, return "true"; else return "false".
-    return PrimitiveString::create(vm, TRY_OR_THROW_OOM(vm, String::from_utf8(b ? "true"sv : "false"sv)));
+    return PrimitiveString::create(vm, b ? "true"_utf16 : "false"_utf16);
 }
 
 // 20.3.3.3 Boolean.prototype.valueOf ( ), https://tc39.es/ecma262/#sec-boolean.prototype.valueof
diff --git a/Libraries/LibJS/Runtime/ConsoleObject.cpp b/Libraries/LibJS/Runtime/ConsoleObject.cpp
index e3aff8f65e..1190bdb60e 100644
--- a/Libraries/LibJS/Runtime/ConsoleObject.cpp
+++ b/Libraries/LibJS/Runtime/ConsoleObject.cpp
@@ -59,7 +59,7 @@ void ConsoleObject::initialize(Realm& realm)
     define_native_function(realm, vm.names.timeLog, time_log, 0, attr);
     define_native_function(realm, vm.names.timeEnd, time_end, 0, attr);
 
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "console"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "console"_utf16_fly_string), Attribute::Configurable);
 }
 
 // 1.1.1. assert(condition, ...data), https://console.spec.whatwg.org/#assert
diff --git a/Libraries/LibJS/Runtime/Date.cpp b/Libraries/LibJS/Runtime/Date.cpp
index a462c53e7e..51819aef15 100644
--- a/Libraries/LibJS/Runtime/Date.cpp
+++ b/Libraries/LibJS/Runtime/Date.cpp
@@ -37,7 +37,7 @@ Date::Date(double date_value, Object& prototype)
 
 Date::~Date() = default;
 
-ErrorOr<Utf16String> Date::iso_date_string() const
+Utf16String Date::iso_date_string() const
 {
     int year = year_from_time(m_date_value);
 
@@ -442,14 +442,18 @@ Unicode::TimeZoneOffset get_named_time_zone_offset_milliseconds(StringView time_
     return offset.release_value();
 }
 
-static Optional<String> cached_system_time_zone_identifier;
+static auto& cached_system_time_zone_identifier()
+{
+    static NeverDestroyed<Optional<Utf16String>> cached_system_time_zone_identifier;
+    return *cached_system_time_zone_identifier;
+}
 
 // 21.4.1.24 SystemTimeZoneIdentifier ( ), https://tc39.es/ecma262/#sec-systemtimezoneidentifier
-String system_time_zone_identifier()
+Utf16String system_time_zone_identifier()
 {
     // OPTIMIZATION: We cache the system time zone to avoid the expensive lookups below.
-    if (cached_system_time_zone_identifier.has_value())
-        return *cached_system_time_zone_identifier;
+    if (cached_system_time_zone_identifier().has_value())
+        return *cached_system_time_zone_identifier();
 
     // 1. If the implementation only supports the UTC time zone, return "UTC".
 
@@ -457,23 +461,22 @@ String system_time_zone_identifier()
     //    time zone identifier or an offset time zone identifier.
     auto system_time_zone_string = Unicode::current_time_zone();
 
-    auto utf16_system_time_zone_string = Utf16String::from_utf8(system_time_zone_string);
-    if (!is_offset_time_zone_identifier(utf16_system_time_zone_string)) {
+    if (!is_offset_time_zone_identifier(system_time_zone_string)) {
         auto time_zone_identifier = Intl::get_available_named_time_zone_identifier(system_time_zone_string);
         if (!time_zone_identifier.has_value())
-            return "UTC"_string;
+            return "UTC"_utf16;
 
         system_time_zone_string = time_zone_identifier->primary_identifier;
     }
 
     // 3. Return systemTimeZoneString.
-    cached_system_time_zone_identifier = move(system_time_zone_string);
-    return *cached_system_time_zone_identifier;
+    cached_system_time_zone_identifier() = move(system_time_zone_string);
+    return *cached_system_time_zone_identifier();
 }
 
 void clear_system_time_zone_cache()
 {
-    cached_system_time_zone_identifier.clear();
+    cached_system_time_zone_identifier().clear();
 }
 
 // 21.4.1.25 LocalTime ( t ), https://tc39.es/ecma262/#sec-localtime
@@ -484,7 +487,7 @@ double local_time(double time)
     auto system_time_zone_identifier = JS::system_time_zone_identifier();
 
     // 2. Let parseResult be ! ParseTimeZoneIdentifier(systemTimeZoneIdentifier).
-    auto parse_result = Temporal::parse_time_zone_identifier(system_time_zone_identifier);
+    auto parse_result = Temporal::parse_time_zone_identifier(system_time_zone_identifier.utf16_view());
 
     double offset_nanoseconds { 0 };
 
@@ -496,7 +499,7 @@ double local_time(double time)
     // 4. Else,
     else {
         // a. Let offsetNs be GetNamedTimeZoneOffsetNanoseconds(systemTimeZoneIdentifier, ℤ(ℝ(t) × 10^6)).
-        auto offset = get_named_time_zone_offset_milliseconds(system_time_zone_identifier, time);
+        auto offset = get_named_time_zone_offset_milliseconds(system_time_zone_identifier.utf16_view().bytes(), time);
         offset_nanoseconds = static_cast<double>(offset.offset.to_nanoseconds());
     }
 
@@ -515,7 +518,7 @@ double utc_time(double time)
     auto system_time_zone_identifier = JS::system_time_zone_identifier();
 
     // 2. Let parseResult be ! ParseTimeZoneIdentifier(systemTimeZoneIdentifier).
-    auto parse_result = Temporal::parse_time_zone_identifier(system_time_zone_identifier);
+    auto parse_result = Temporal::parse_time_zone_identifier(system_time_zone_identifier.utf16_view());
 
     double offset_nanoseconds { 0 };
 
@@ -530,7 +533,7 @@ double utc_time(double time)
         auto iso_date_time = Temporal::time_value_to_iso_date_time_record(time);
 
         // b. Let possibleInstants be GetNamedTimeZoneEpochNanoseconds(systemTimeZoneIdentifier, isoDateTime).
-        auto possible_instants = get_named_time_zone_epoch_nanoseconds(system_time_zone_identifier, iso_date_time);
+        auto possible_instants = get_named_time_zone_epoch_nanoseconds(system_time_zone_identifier.utf16_view().bytes(), iso_date_time);
 
         // c. NOTE: The following steps ensure that when t represents local time repeating multiple times at a negative
         //    time zone transition (e.g. when the daylight saving time ends or the time zone offset is decreased due to
@@ -565,7 +568,7 @@ double utc_time(double time)
         }
 
         // f. Let offsetNs be GetNamedTimeZoneOffsetNanoseconds(systemTimeZoneIdentifier, disambiguatedInstant).
-        auto offset = get_named_time_zone_offset_nanoseconds(system_time_zone_identifier, disambiguated_instant);
+        auto offset = get_named_time_zone_offset_nanoseconds(system_time_zone_identifier.utf16_view().bytes(), disambiguated_instant);
         offset_nanoseconds = static_cast<double>(offset.offset.to_nanoseconds());
     }
 
diff --git a/Libraries/LibJS/Runtime/Date.h b/Libraries/LibJS/Runtime/Date.h
index 4c92ce1895..3c02743a1c 100644
--- a/Libraries/LibJS/Runtime/Date.h
+++ b/Libraries/LibJS/Runtime/Date.h
@@ -7,6 +7,7 @@
 
 #pragma once
 
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 #include <LibCrypto/BigInt/SignedBigInteger.h>
 #include <LibJS/Export.h>
@@ -28,7 +29,7 @@ public:
     double date_value() const { return m_date_value; }
     void set_date_value(double value) { m_date_value = value; }
 
-    ErrorOr<Utf16String> iso_date_string() const;
+    Utf16String iso_date_string() const;
 
 private:
     Date(double date_value, Object& prototype);
@@ -43,8 +44,8 @@ inline bool Object::fast_is<Date>() const { return is_date(); }
 
 // 21.4.1.22 Time Zone Identifier Record, https://tc39.es/ecma262/#sec-time-zone-identifier-record
 struct TimeZoneIdentifier {
-    String identifier;         // [[Identifier]]
-    String primary_identifier; // [[PrimaryIdentifier]]
+    Utf16String identifier;         // [[Identifier]]
+    Utf16String primary_identifier; // [[PrimaryIdentifier]]
 };
 
 // https://tc39.es/ecma262/#eqn-HoursPerDay
@@ -90,7 +91,7 @@ i64 clip_double_to_sane_time(double value);
 Vector<Crypto::SignedBigInteger> get_named_time_zone_epoch_nanoseconds(StringView time_zone_identifier, Temporal::ISODateTime const&);
 Unicode::TimeZoneOffset get_named_time_zone_offset_nanoseconds(StringView time_zone_identifier, Crypto::SignedBigInteger const& epoch_nanoseconds);
 Unicode::TimeZoneOffset get_named_time_zone_offset_milliseconds(StringView time_zone_identifier, double epoch_milliseconds);
-String system_time_zone_identifier();
+Utf16String system_time_zone_identifier();
 JS_API void clear_system_time_zone_cache();
 double local_time(double time);
 double utc_time(double time);
diff --git a/Libraries/LibJS/Runtime/DatePrototype.cpp b/Libraries/LibJS/Runtime/DatePrototype.cpp
index 77c4630b28..365e7712a6 100644
--- a/Libraries/LibJS/Runtime/DatePrototype.cpp
+++ b/Libraries/LibJS/Runtime/DatePrototype.cpp
@@ -7,7 +7,6 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/ByteString.h>
 #include <AK/DateConstants.h>
 #include <AK/Function.h>
 #include <AK/TypeCasts.h>
@@ -955,11 +954,12 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_date_string)
 
     // 3. If tv is NaN, return "Invalid Date".
     if (isnan(time))
-        return PrimitiveString::create(vm, "Invalid Date"_string);
+        return PrimitiveString::create(vm, "Invalid Date"_utf16_fly_string);
 
     // 4. Let t be LocalTime(tv).
     // 5. Return DateString(t).
-    return PrimitiveString::create(vm, date_string(local_time(time)));
+    auto string = date_string(local_time(time));
+    return PrimitiveString::create(vm, move(string));
 }
 
 // 21.4.4.36 Date.prototype.toISOString ( ), https://tc39.es/ecma262/#sec-date.prototype.toisostring
@@ -970,7 +970,7 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_iso_string)
     if (!Value(this_object->date_value()).is_finite_number())
         return vm.throw_completion<RangeError>(ErrorType::InvalidTimeValue);
 
-    auto string = TRY_OR_THROW_OOM(vm, this_object->iso_date_string());
+    auto string = this_object->iso_date_string();
     return PrimitiveString::create(vm, move(string));
 }
 
@@ -1001,7 +1001,7 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_locale_date_string)
 
     // 2. If x is NaN, return "Invalid Date".
     if (isnan(time))
-        return PrimitiveString::create(vm, "Invalid Date"_string);
+        return PrimitiveString::create(vm, "Invalid Date"_utf16_fly_string);
 
     // 3. Let dateFormat be ? CreateDateTimeFormat(%DateTimeFormat%, locales, options, "date", "date").
     auto date_format = TRY(Intl::create_date_time_format(vm, realm.intrinsics().intl_date_time_format_constructor(), locales, options, Intl::OptionRequired::Date, Intl::OptionDefaults::Date));
@@ -1025,7 +1025,7 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_locale_string)
 
     // 2. If x is NaN, return "Invalid Date".
     if (isnan(time))
-        return PrimitiveString::create(vm, "Invalid Date"_string);
+        return PrimitiveString::create(vm, "Invalid Date"_utf16_fly_string);
 
     // 3. Let dateFormat be ? CreateDateTimeFormat(%DateTimeFormat%, locales, options, "any", "all").
     auto date_format = TRY(Intl::create_date_time_format(vm, realm.intrinsics().intl_date_time_format_constructor(), locales, options, Intl::OptionRequired::Any, Intl::OptionDefaults::All));
@@ -1049,7 +1049,7 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_locale_time_string)
 
     // 2. If x is NaN, return "Invalid Date".
     if (isnan(time))
-        return PrimitiveString::create(vm, "Invalid Date"_string);
+        return PrimitiveString::create(vm, "Invalid Date"_utf16_fly_string);
 
     // 3. Let timeFormat be ? CreateDateTimeFormat(%DateTimeFormat%, locales, options, "time", "time").
     auto time_format = TRY(Intl::create_date_time_format(vm, realm.intrinsics().intl_date_time_format_constructor(), locales, options, Intl::OptionRequired::Time, Intl::OptionDefaults::Time));
@@ -1071,17 +1071,17 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_string)
 
 // 21.4.4.41.1 TimeString ( tv ), https://tc39.es/ecma262/#sec-timestring
 // 14.5.8 TimeString ( tv ), https://tc39.es/proposal-temporal/#sec-timestring
-ByteString time_string(double time)
+Utf16String time_string(double time)
 {
     // 1. Let timeString be FormatTimeString(ℝ(HourFromTime(tv)), ℝ(MinFromTime(tv)), ℝ(SecFromTime(tv)), 0, 0).
     auto time_string = Temporal::format_time_string(hour_from_time(time), min_from_time(time), sec_from_time(time), 0, 0);
 
     // 4. Return the string-concatenation of timeString, the code unit 0x0020 (SPACE), and "GMT".
-    return ByteString::formatted("{} GMT", time_string);
+    return Utf16String::formatted("{} GMT", time_string);
 }
 
 // 21.4.4.41.2 DateString ( tv ), https://tc39.es/ecma262/#sec-datestring
-ByteString date_string(double time)
+Utf16String date_string(double time)
 {
     // 1. Let weekday be the Name of the entry in Table 62 with the Number WeekDay(tv).
     auto weekday = short_day_names[week_day(time)];
@@ -1100,7 +1100,7 @@ ByteString date_string(double time)
 
     // 6. Let paddedYear be ToZeroPaddedDecimalString(abs(ℝ(yv)), 4).
     // 7. Return the string-concatenation of weekday, the code unit 0x0020 (SPACE), month, the code unit 0x0020 (SPACE), day, the code unit 0x0020 (SPACE), yearSign, and paddedYear.
-    return ByteString::formatted("{} {} {:02} {}{:04}", weekday, month, day, year_sign, abs(year));
+    return Utf16String::formatted("{} {} {:02} {}{:04}", weekday, month, day, year_sign, abs(year));
 }
 
 // 21.4.4.41.3 TimeZoneString ( tv ), https://tc39.es/ecma262/#sec-timezoneestring
@@ -1111,13 +1111,13 @@ Utf16String time_zone_string(double time)
     auto system_time_zone_identifier = JS::system_time_zone_identifier();
 
     // 2. Let offsetMinutes be ! ParseTimeZoneIdentifier(systemTimeZoneIdentifier).[[OffsetMinutes]].
-    auto offset_minutes = Temporal::parse_time_zone_identifier(system_time_zone_identifier).offset_minutes;
+    auto offset_minutes = Temporal::parse_time_zone_identifier(system_time_zone_identifier.utf16_view()).offset_minutes;
     auto in_dst = Unicode::TimeZoneOffset::InDST::No;
 
     // 2. If offsetMinutes is EMPTY, then
     if (!offset_minutes.has_value()) {
         // a. Let offsetNs be GetNamedTimeZoneOffsetNanoseconds(systemTimeZoneIdentifier, ℤ(ℝ(tv) × 10^6)).
-        auto offset = get_named_time_zone_offset_milliseconds(system_time_zone_identifier, time);
+        auto offset = get_named_time_zone_offset_milliseconds(system_time_zone_identifier.utf16_view().bytes(), time);
         in_dst = offset.in_dst;
 
         // b. Set offsetMinutes to truncate(offsetNs / (60 × 10**9)).
@@ -1130,11 +1130,10 @@ Utf16String time_zone_string(double time)
     // 5. Let tzName be an implementation-defined string that is either the empty String or the string-concatenation of
     //    the code unit 0x0020 (SPACE), the code unit 0x0028 (LEFT PARENTHESIS), an implementation-defined timezone name,
     //    and the code unit 0x0029 (RIGHT PARENTHESIS).
-    auto time_zone_identifier = Unicode::current_time_zone();
-    auto tz_name = Utf16String::from_utf8(time_zone_identifier);
+    auto tz_name = Unicode::current_time_zone();
 
     // Most implementations seem to prefer the long-form display name of the time zone. Not super important, but we may as well match that behavior.
-    if (auto name = Unicode::time_zone_display_name(Unicode::default_locale(), time_zone_identifier, in_dst, time); name.has_value())
+    if (auto name = Unicode::time_zone_display_name(Unicode::default_locale().bytes(), tz_name.utf16_view().bytes(), in_dst, time); name.has_value())
         tz_name = name.release_value();
 
     // 10. Return the string-concatenation of offsetString and tzName.
@@ -1164,7 +1163,7 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_time_string)
 
     // 3. If tv is NaN, return "Invalid Date".
     if (isnan(time))
-        return PrimitiveString::create(vm, "Invalid Date"_string);
+        return PrimitiveString::create(vm, "Invalid Date"_utf16_fly_string);
 
     // 4. Let t be LocalTime(tv).
     // 5. Return the string-concatenation of TimeString(t) and TimeZoneString(tv).
@@ -1181,7 +1180,7 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_utc_string)
 
     // 3. If tv is NaN, return "Invalid Date".
     if (isnan(time))
-        return PrimitiveString::create(vm, "Invalid Date"_string);
+        return PrimitiveString::create(vm, "Invalid Date"_utf16_fly_string);
 
     // 4. Let weekday be the Name of the entry in Table 62 with the Number WeekDay(tv).
     auto weekday = short_day_names[week_day(time)];
@@ -1200,7 +1199,7 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_utc_string)
 
     // 9. Let paddedYear be ToZeroPaddedDecimalString(abs(ℝ(yv)), 4).
     // 10. Return the string-concatenation of weekday, ",", the code unit 0x0020 (SPACE), day, the code unit 0x0020 (SPACE), month, the code unit 0x0020 (SPACE), yearSign, paddedYear, the code unit 0x0020 (SPACE), and TimeString(tv).
-    auto string = ByteString::formatted("{}, {:02} {} {}{:04} {}", weekday, day, month, year_sign, abs(year), time_string(time));
+    auto string = Utf16String::formatted("{}, {:02} {} {}{:04} {}", weekday, day, month, year_sign, abs(year), time_string(time));
     return PrimitiveString::create(vm, move(string));
 }
 
diff --git a/Libraries/LibJS/Runtime/DatePrototype.h b/Libraries/LibJS/Runtime/DatePrototype.h
index 90d1495fe6..6fe55e1d70 100644
--- a/Libraries/LibJS/Runtime/DatePrototype.h
+++ b/Libraries/LibJS/Runtime/DatePrototype.h
@@ -76,8 +76,8 @@ private:
 };
 
 ThrowCompletionOr<double> this_time_value(VM&, Value value);
-ByteString time_string(double time);
-ByteString date_string(double time);
+Utf16String time_string(double time);
+Utf16String date_string(double time);
 Utf16String time_zone_string(double time);
 Utf16String to_date_string(double time);
 
diff --git a/Libraries/LibJS/Runtime/Error.cpp b/Libraries/LibJS/Runtime/Error.cpp
index 9721ea189d..42d1a0616a 100644
--- a/Libraries/LibJS/Runtime/Error.cpp
+++ b/Libraries/LibJS/Runtime/Error.cpp
@@ -25,6 +25,13 @@ GC::Ref<Error> Error::create(Realm& realm, Utf16String message)
     return error;
 }
 
+GC::Ref<Error> Error::create(Realm& realm, Utf16View message)
+{
+    auto error = Error::create(realm);
+    error->set_message(message);
+    return error;
+}
+
 GC::Ref<Error> Error::create(Realm& realm, StringView message)
 {
     return create(realm, Utf16String::from_utf8(message));
@@ -78,6 +85,14 @@ void Error::set_message(Utf16String message)
     define_direct_property(vm.names.message, PrimitiveString::create(vm, move(message)), attr);
 }
 
+void Error::set_message(Utf16View message)
+{
+    auto& vm = this->vm();
+
+    u8 attr = Attribute::Writable | Attribute::Configurable;
+    define_direct_property(vm.names.message, PrimitiveString::create(vm, message), attr);
+}
+
 #define __JS_ENUMERATE(ClassName, snake_name, PrototypeName, ConstructorName, ArrayType) \
     GC_DEFINE_ALLOCATOR(ClassName);                                                      \
     GC::Ref<ClassName> ClassName::create(Realm& realm)                                   \
@@ -92,6 +107,13 @@ void Error::set_message(Utf16String message)
         return error;                                                                    \
     }                                                                                    \
                                                                                          \
+    GC::Ref<ClassName> ClassName::create(Realm& realm, Utf16View message)                \
+    {                                                                                    \
+        auto error = ClassName::create(realm);                                           \
+        error->set_message(message);                                                     \
+        return error;                                                                    \
+    }                                                                                    \
+                                                                                         \
     GC::Ref<ClassName> ClassName::create(Realm& realm, StringView message)               \
     {                                                                                    \
         return create(realm, Utf16String::from_utf8(message));                           \
diff --git a/Libraries/LibJS/Runtime/Error.h b/Libraries/LibJS/Runtime/Error.h
index 7fe6aff4d2..464518a93e 100644
--- a/Libraries/LibJS/Runtime/Error.h
+++ b/Libraries/LibJS/Runtime/Error.h
@@ -26,6 +26,7 @@ class JS_API Error
 public:
     static GC::Ref<Error> create(Realm&);
     static GC::Ref<Error> create(Realm&, Utf16String message);
+    static GC::Ref<Error> create(Realm&, Utf16View message);
     static GC::Ref<Error> create(Realm&, StringView message);
 
     virtual ~Error() override = default;
@@ -35,6 +36,7 @@ public:
     ThrowCompletionOr<void> install_error_cause(Value options);
 
     void set_message(Utf16String);
+    void set_message(Utf16View);
 
 protected:
     explicit Error(Object& prototype);
@@ -62,6 +64,7 @@ inline bool Object::fast_is<Error>() const { return is_error_object(); }
     public:                                                                         \
         static GC::Ref<ClassName> create(Realm&);                                   \
         static GC::Ref<ClassName> create(Realm&, Utf16String message);              \
+        static GC::Ref<ClassName> create(Realm&, Utf16View message);                \
         static GC::Ref<ClassName> create(Realm&, StringView message);               \
                                                                                     \
         explicit ClassName(Object& prototype);                                      \
diff --git a/Libraries/LibJS/Runtime/ErrorPrototype.cpp b/Libraries/LibJS/Runtime/ErrorPrototype.cpp
index 040a4580a9..5647867d1d 100644
--- a/Libraries/LibJS/Runtime/ErrorPrototype.cpp
+++ b/Libraries/LibJS/Runtime/ErrorPrototype.cpp
@@ -26,7 +26,7 @@ void ErrorPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
     Base::initialize(realm);
     u8 attr = Attribute::Writable | Attribute::Configurable;
-    define_direct_property(vm.names.name, PrimitiveString::create(vm, "Error"_string), attr);
+    define_direct_property(vm.names.name, PrimitiveString::create(vm, "Error"_utf16_fly_string), attr);
     define_direct_property(vm.names.message, PrimitiveString::create(vm, Utf16String {}), attr);
     define_native_function(realm, vm.names.toString, to_string, 0, attr);
     // Non standard property "stack"
@@ -131,21 +131,21 @@ JS_DEFINE_NATIVE_FUNCTION(ErrorPrototype::stack_setter)
     return TRY(this_object.create_data_property_or_throw(vm.names.stack, vm.argument(0)));
 }
 
-#define __JS_ENUMERATE(ClassName, snake_name, PrototypeName, ConstructorName, ArrayType)               \
-    GC_DEFINE_ALLOCATOR(PrototypeName);                                                                \
-                                                                                                       \
-    PrototypeName::PrototypeName(Realm& realm)                                                         \
-        : PrototypeObject(realm.intrinsics().error_prototype())                                        \
-    {                                                                                                  \
-    }                                                                                                  \
-                                                                                                       \
-    void PrototypeName::initialize(Realm& realm)                                                       \
-    {                                                                                                  \
-        auto& vm = this->vm();                                                                         \
-        Base::initialize(realm);                                                                       \
-        u8 attr = Attribute::Writable | Attribute::Configurable;                                       \
-        define_direct_property(vm.names.name, PrimitiveString::create(vm, #ClassName##_string), attr); \
-        define_direct_property(vm.names.message, PrimitiveString::create(vm, Utf16String {}), attr);   \
+#define __JS_ENUMERATE(ClassName, snake_name, PrototypeName, ConstructorName, ArrayType)                         \
+    GC_DEFINE_ALLOCATOR(PrototypeName);                                                                          \
+                                                                                                                 \
+    PrototypeName::PrototypeName(Realm& realm)                                                                   \
+        : PrototypeObject(realm.intrinsics().error_prototype())                                                  \
+    {                                                                                                            \
+    }                                                                                                            \
+                                                                                                                 \
+    void PrototypeName::initialize(Realm& realm)                                                                 \
+    {                                                                                                            \
+        auto& vm = this->vm();                                                                                   \
+        Base::initialize(realm);                                                                                 \
+        u8 attr = Attribute::Writable | Attribute::Configurable;                                                 \
+        define_direct_property(vm.names.name, PrimitiveString::create(vm, #ClassName##_utf16_fly_string), attr); \
+        define_direct_property(vm.names.message, PrimitiveString::create(vm, Utf16String {}), attr);             \
     }
 
 JS_ENUMERATE_NATIVE_ERRORS
diff --git a/Libraries/LibJS/Runtime/ErrorTypes.cpp b/Libraries/LibJS/Runtime/ErrorTypes.cpp
index 0ad1bb7b42..2a3ed2294a 100644
--- a/Libraries/LibJS/Runtime/ErrorTypes.cpp
+++ b/Libraries/LibJS/Runtime/ErrorTypes.cpp
@@ -9,15 +9,8 @@
 namespace JS {
 
 #define __ENUMERATE_JS_ERROR(name, message) \
-    ErrorType const& ErrorType::name = *new ErrorType(message##sv);
+    ErrorType const& ErrorType::name = *new ErrorType(message##sv, Utf16View { message##sv });
 JS_ENUMERATE_ERROR_TYPES(__ENUMERATE_JS_ERROR)
 #undef __ENUMERATE_JS_ERROR
 
-Utf16String const& ErrorType::message() const
-{
-    if (m_message.is_empty())
-        m_message = Utf16String::from_utf8_without_validation(m_format);
-    return m_message;
-}
-
 }
diff --git a/Libraries/LibJS/Runtime/ErrorTypes.h b/Libraries/LibJS/Runtime/ErrorTypes.h
index 01f979f8b9..1784ccbda8 100644
--- a/Libraries/LibJS/Runtime/ErrorTypes.h
+++ b/Libraries/LibJS/Runtime/ErrorTypes.h
@@ -8,6 +8,7 @@
 
 #include <AK/StringView.h>
 #include <AK/Utf16String.h>
+#include <AK/Utf16View.h>
 #include <LibJS/Export.h>
 
 #define JS_ENUMERATE_ERROR_TYPES(M)                                                                                                 \
@@ -320,16 +321,17 @@ public:
 #undef __ENUMERATE_JS_ERROR
 
     StringView format() const { return m_format; }
-    Utf16String const& message() const;
+    Utf16View message() const { return m_message; }
 
 private:
-    explicit ErrorType(StringView format)
+    explicit ErrorType(StringView format, Utf16View message)
         : m_format(format)
+        , m_message(message)
     {
     }
 
     StringView m_format;
-    mutable Utf16String m_message;
+    Utf16View m_message;
 };
 
 }
diff --git a/Libraries/LibJS/Runtime/FunctionConstructor.cpp b/Libraries/LibJS/Runtime/FunctionConstructor.cpp
index 6425f1252a..7c06d7ed09 100644
--- a/Libraries/LibJS/Runtime/FunctionConstructor.cpp
+++ b/Libraries/LibJS/Runtime/FunctionConstructor.cpp
@@ -152,7 +152,7 @@ ThrowCompletionOr<GC::Ref<ECMAScriptFunctionObject>> FunctionConstructor::create
 
     auto rust_compilation = RustIntegration::compile_dynamic_function(vm, source_text, parameters_string, body_parse_string, kind);
     if (!rust_compilation.has_value())
-        return vm.throw_completion<SyntaxError>("Failed to compile dynamic function"_string);
+        return vm.throw_completion<SyntaxError>("Failed to compile dynamic function"_utf16);
     if (rust_compilation->is_error())
         return vm.throw_completion<SyntaxError>(rust_compilation->release_error());
     function_data = rust_compilation->value();
diff --git a/Libraries/LibJS/Runtime/FunctionPrototype.cpp b/Libraries/LibJS/Runtime/FunctionPrototype.cpp
index 23a749603c..8484d56071 100644
--- a/Libraries/LibJS/Runtime/FunctionPrototype.cpp
+++ b/Libraries/LibJS/Runtime/FunctionPrototype.cpp
@@ -35,7 +35,7 @@ void FunctionPrototype::initialize(Realm& realm)
     define_native_function(realm, vm.names.toString, to_string, 0, attr);
     define_native_function(realm, vm.well_known_symbol_has_instance(), symbol_has_instance, 1, 0, Bytecode::Builtin::OrdinaryHasInstance);
     define_direct_property(vm.names.length, Value(0), Attribute::Configurable);
-    define_direct_property(vm.names.name, PrimitiveString::create(vm, String {}), Attribute::Configurable);
+    define_direct_property(vm.names.name, PrimitiveString::create(vm, Utf16String {}), Attribute::Configurable);
 }
 
 ThrowCompletionOr<Value> FunctionPrototype::internal_call(ExecutionContext&, Value)
@@ -214,12 +214,12 @@ JS_DEFINE_NATIVE_FUNCTION(FunctionPrototype::to_string)
     if (auto const* native_function = as_if<NativeFunction>(function)) {
         // NOTE: once we remove name(), the fallback here can simply be an empty string.
         auto const name = native_function->initial_name().value_or(native_function->name());
-        return PrimitiveString::create(vm, ByteString::formatted("function {}() {{ [native code] }}", name));
+        return PrimitiveString::create(vm, Utf16String::formatted("function {}() {{ [native code] }}", name));
     }
 
     // 4. If Type(func) is Object and IsCallable(func) is true, return an implementation-defined String source code representation of func. The representation must have the syntax of a NativeFunction.
     // NOTE: ProxyObject, BoundFunction, WrappedFunction
-    return PrimitiveString::create(vm, "function () { [native code] }"_string);
+    return PrimitiveString::create(vm, "function () { [native code] }"_utf16_fly_string);
 }
 
 // 20.2.3.6 Function.prototype [ @@hasInstance ] ( V ), https://tc39.es/ecma262/#sec-function.prototype-@@hasinstance
diff --git a/Libraries/LibJS/Runtime/GeneratorFunctionPrototype.cpp b/Libraries/LibJS/Runtime/GeneratorFunctionPrototype.cpp
index d53c7eb2fa..971124ca7d 100644
--- a/Libraries/LibJS/Runtime/GeneratorFunctionPrototype.cpp
+++ b/Libraries/LibJS/Runtime/GeneratorFunctionPrototype.cpp
@@ -25,7 +25,7 @@ void GeneratorFunctionPrototype::initialize(Realm& realm)
     // 27.3.3.2 GeneratorFunction.prototype.prototype, https://tc39.es/ecma262/#sec-generatorfunction.prototype.prototype
     define_direct_property(vm.names.prototype, realm.intrinsics().generator_prototype(), Attribute::Configurable);
     // 27.3.3.3 GeneratorFunction.prototype [ @@toStringTag ], https://tc39.es/ecma262/#sec-generatorfunction.prototype-@@tostringtag
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "GeneratorFunction"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "GeneratorFunction"_utf16_fly_string), Attribute::Configurable);
 }
 
 }
diff --git a/Libraries/LibJS/Runtime/GeneratorPrototype.cpp b/Libraries/LibJS/Runtime/GeneratorPrototype.cpp
index 7cedd52a84..f54751dd6f 100644
--- a/Libraries/LibJS/Runtime/GeneratorPrototype.cpp
+++ b/Libraries/LibJS/Runtime/GeneratorPrototype.cpp
@@ -27,7 +27,7 @@ void GeneratorPrototype::initialize(Realm& realm)
     define_native_function(realm, vm.names.throw_, throw_, 1, attr);
 
     // 27.5.1.5 Generator.prototype [ @@toStringTag ], https://tc39.es/ecma262/#sec-generator.prototype-@@tostringtag
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Generator"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Generator"_utf16_fly_string), Attribute::Configurable);
 }
 
 static Value generator_resume_result_to_value(VM& vm, GeneratorObject::IterationResult const& iteration_result)
diff --git a/Libraries/LibJS/Runtime/GlobalObject.cpp b/Libraries/LibJS/Runtime/GlobalObject.cpp
index 85766eac4f..ca4daad9da 100644
--- a/Libraries/LibJS/Runtime/GlobalObject.cpp
+++ b/Libraries/LibJS/Runtime/GlobalObject.cpp
@@ -10,6 +10,7 @@
 #include <AK/Hex.h>
 #include <AK/StringConversions.h>
 #include <AK/UnicodeUtils.h>
+#include <AK/Utf16StringBuilder.h>
 #include <AK/Utf16View.h>
 #include <AK/Utf8View.h>
 #include <LibGC/DeferGC.h>
@@ -366,15 +367,13 @@ JS_DEFINE_NATIVE_FUNCTION(GlobalObject::parse_int)
 }
 
 // 19.2.6.5 Encode ( string, extraUnescaped ), https://tc39.es/ecma262/#sec-encode
-static ThrowCompletionOr<ByteString> encode(VM& vm, ByteString const& string, StringView unescaped_set)
+static ThrowCompletionOr<Utf16String> encode(VM& vm, Utf16View const& string, StringView unescaped_set)
 {
-    auto utf16_string = Utf16String::from_utf8(string);
-
     // 1. Let strLen be the length of string.
-    auto string_length = utf16_string.length_in_code_units();
+    auto string_length = string.length_in_code_units();
 
     // 2. Let R be the empty String.
-    StringBuilder encoded_builder;
+    StringBuilder encoded_builder(StringBuilder::Mode::UTF16);
 
     // 3. Let alwaysUnescaped be the string-concatenation of the ASCII word characters and "-.!~*'()".
     // 4. Let unescapedSet be the string-concatenation of alwaysUnescaped and extraUnescaped.
@@ -389,7 +388,7 @@ static ThrowCompletionOr<ByteString> encode(VM& vm, ByteString const& string, St
         // Handled below
 
         // b. Let C be the code unit at index k within string.
-        auto code_unit = utf16_string.code_unit_at(k);
+        auto code_unit = string.code_unit_at(k);
         // c. If C is in unescapedSet, then
         // NOTE: We assume the unescaped set only contains ascii characters as unescaped_set is a StringView.
         if (code_unit < 0x80 && unescaped_set.contains(static_cast<char>(code_unit))) {
@@ -402,7 +401,7 @@ static ThrowCompletionOr<ByteString> encode(VM& vm, ByteString const& string, St
         // d. Else,
         else {
             // i. Let cp be CodePointAt(string, k).
-            auto code_point = code_point_at(utf16_string, k);
+            auto code_point = code_point_at(string, k);
             // ii. If cp.[[IsUnpairedSurrogate]] is true, throw a URIError exception.
             if (code_point.is_unpaired_surrogate)
                 return vm.throw_completion<URIError>(ErrorType::URIMalformed);
@@ -420,78 +419,79 @@ static ThrowCompletionOr<ByteString> encode(VM& vm, ByteString const& string, St
             VERIFY(nwritten > 0);
         }
     }
-    return encoded_builder.to_byte_string();
+    return encoded_builder.to_utf16_string();
+}
+
+static ThrowCompletionOr<u8> decode_percent_encoded_byte(VM& vm, Utf16View const& string, size_t percent_index)
+{
+    if (percent_index + 2 >= string.length_in_code_units())
+        return vm.throw_completion<URIError>(ErrorType::URIMalformed);
+
+    auto first_digit = string.code_unit_at(percent_index + 1);
+    if (!is_ascii_hex_digit(first_digit))
+        return vm.throw_completion<URIError>(ErrorType::URIMalformed);
+
+    auto second_digit = string.code_unit_at(percent_index + 2);
+    if (!is_ascii_hex_digit(second_digit))
+        return vm.throw_completion<URIError>(ErrorType::URIMalformed);
+
+    return (parse_ascii_hex_digit(first_digit) << 4) | parse_ascii_hex_digit(second_digit);
 }
 
 // 19.2.6.6 Decode ( string, preserveEscapeSet ), https://tc39.es/ecma262/#sec-decode
 // FIXME: Add spec comments to this implementation. It deviates a lot, so that's a bit tricky.
-static ThrowCompletionOr<ByteString> decode(VM& vm, ByteString const& string, StringView reserved_set)
+static ThrowCompletionOr<Utf16String> decode(VM& vm, Utf16View const& string, StringView reserved_set)
 {
-    StringBuilder decoded_builder;
-    auto code_point_start_offset = 0u;
-    auto expected_continuation_bytes = 0;
-    for (size_t k = 0; k < string.length(); k++) {
-        auto code_unit = string[k];
+    Utf16StringBuilder decoded_builder;
+    for (size_t k = 0; k < string.length_in_code_units(); ++k) {
+        auto code_unit = string.code_unit_at(k);
         if (code_unit != '%') {
-            if (expected_continuation_bytes > 0)
-                return vm.throw_completion<URIError>(ErrorType::URIMalformed);
-
-            decoded_builder.append(code_unit);
+            decoded_builder.append_code_unit(code_unit);
             continue;
         }
 
-        if (k + 2 >= string.length())
-            return vm.throw_completion<URIError>(ErrorType::URIMalformed);
-
-        auto first_digit = decode_hex_digit(string[k + 1]);
-        if (first_digit >= 16)
-            return vm.throw_completion<URIError>(ErrorType::URIMalformed);
-
-        auto second_digit = decode_hex_digit(string[k + 2]);
-        if (second_digit >= 16)
-            return vm.throw_completion<URIError>(ErrorType::URIMalformed);
-
-        u8 decoded_code_unit = (first_digit << 4) | second_digit;
+        auto decoded_code_unit = TRY(decode_percent_encoded_byte(vm, string, k));
         k += 2;
-        if (expected_continuation_bytes > 0) {
-            decoded_builder.append(decoded_code_unit);
-            expected_continuation_bytes--;
-            if (expected_continuation_bytes == 0 && !Utf8View(decoded_builder.string_view().substring_view(code_point_start_offset)).validate(AllowLonelySurrogates::No))
-                return vm.throw_completion<URIError>(ErrorType::URIMalformed);
-            continue;
-        }
 
         if (decoded_code_unit < 0x80) {
             if (reserved_set.contains(static_cast<char>(decoded_code_unit)))
                 decoded_builder.append(string.substring_view(k - 2, 3));
             else
-                decoded_builder.append(decoded_code_unit);
+                decoded_builder.append_code_unit(decoded_code_unit);
             continue;
         }
 
-        auto leading_ones = count_leading_zeroes_safe(static_cast<u8>(~decoded_code_unit));
+        auto leading_ones = static_cast<size_t>(count_leading_zeroes_safe(static_cast<u8>(~decoded_code_unit)));
         if (leading_ones == 1 || leading_ones > 4)
             return vm.throw_completion<URIError>(ErrorType::URIMalformed);
 
-        code_point_start_offset = decoded_builder.length();
-        decoded_builder.append(decoded_code_unit);
-        expected_continuation_bytes = leading_ones - 1;
+        u8 utf8_bytes[4] { decoded_code_unit };
+        for (auto byte_index = 1u; byte_index < leading_ones; ++byte_index) {
+            if (k + 3 >= string.length_in_code_units() || string.code_unit_at(k + 1) != '%')
+                return vm.throw_completion<URIError>(ErrorType::URIMalformed);
+            utf8_bytes[byte_index] = TRY(decode_percent_encoded_byte(vm, string, k + 1));
+            k += 3;
+        }
+
+        auto utf8_view = Utf8View { StringView { reinterpret_cast<char const*>(utf8_bytes), leading_ones } };
+        if (!utf8_view.validate(AllowLonelySurrogates::No))
+            return vm.throw_completion<URIError>(ErrorType::URIMalformed);
+        for (auto decoded_code_point : utf8_view)
+            decoded_builder.append_code_point(decoded_code_point);
     }
-    if (expected_continuation_bytes > 0)
-        return vm.throw_completion<URIError>(ErrorType::URIMalformed);
-    return decoded_builder.to_byte_string();
+    return decoded_builder.to_string();
 }
 
 // 19.2.6.1 decodeURI ( encodedURI ), https://tc39.es/ecma262/#sec-decodeuri-encodeduri
 JS_DEFINE_NATIVE_FUNCTION(GlobalObject::decode_uri)
 {
     // 1. Let uriString be ? ToString(encodedURI).
-    auto uri_string = TRY(vm.argument(0).to_byte_string(vm));
+    auto uri_string = TRY(vm.argument(0).to_utf16_string(vm));
 
     // 2. Let preserveEscapeSet be ";/?:@&=+$,#".
     // 3. Return ? Decode(uriString, preserveEscapeSet).
-    auto decoded = TRY(decode(vm, uri_string, ";/?:@&=+$,#"sv));
-    return PrimitiveString::create(vm, move(decoded));
+    auto decoded = TRY(decode(vm, uri_string.utf16_view(), ";/?:@&=+$,#"sv));
+    return PrimitiveString::create(vm, decoded);
 }
 
 // 19.2.6.2 decodeURIComponent ( encodedURIComponent ), https://tc39.es/ecma262/#sec-decodeuricomponent-encodeduricomponent
@@ -500,12 +500,12 @@ JS_DEFINE_NATIVE_FUNCTION(GlobalObject::decode_uri_component)
     auto encoded_uri_component = vm.argument(0);
 
     // 1. Let componentString be ? ToString(encodedURIComponent).
-    auto uri_string = TRY(encoded_uri_component.to_byte_string(vm));
+    auto uri_string = TRY(encoded_uri_component.to_utf16_string(vm));
 
     // 2. Let preserveEscapeSet be the empty String.
     // 3. Return ? Decode(componentString, preserveEscapeSet).
-    auto decoded = TRY(decode(vm, uri_string, ""sv));
-    return PrimitiveString::create(vm, move(decoded));
+    auto decoded = TRY(decode(vm, uri_string.utf16_view(), ""sv));
+    return PrimitiveString::create(vm, decoded);
 }
 
 // 19.2.6.3 encodeURI ( uri ), https://tc39.es/ecma262/#sec-encodeuri-uri
@@ -514,11 +514,11 @@ JS_DEFINE_NATIVE_FUNCTION(GlobalObject::encode_uri)
     auto uri = vm.argument(0);
 
     // 1. Let uriString be ? ToString(uri).
-    auto uri_string = TRY(uri.to_byte_string(vm));
+    auto uri_string = TRY(uri.to_utf16_string(vm));
 
     // 2. Let extraUnescaped be ";/?:@&=+$,#".
     // 3. Return ? Encode(uriString, extraUnescaped).
-    auto encoded = TRY(encode(vm, uri_string, ";/?:@&=+$,abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_.!~*'()#"sv));
+    auto encoded = TRY(encode(vm, uri_string.utf16_view(), ";/?:@&=+$,abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_.!~*'()#"sv));
     return PrimitiveString::create(vm, move(encoded));
 }
 
@@ -528,11 +528,11 @@ JS_DEFINE_NATIVE_FUNCTION(GlobalObject::encode_uri_component)
     auto uri_component = vm.argument(0);
 
     // 1. Let componentString be ? ToString(uriComponent).
-    auto uri_string = TRY(uri_component.to_byte_string(vm));
+    auto uri_string = TRY(uri_component.to_utf16_string(vm));
 
     // 2. Let extraUnescaped be the empty String.
     // 3. Return ? Encode(componentString, extraUnescaped).
-    auto encoded = TRY(encode(vm, uri_string, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_.!~*'()"sv));
+    auto encoded = TRY(encode(vm, uri_string.utf16_view(), "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_.!~*'()"sv));
     return PrimitiveString::create(vm, move(encoded));
 }
 
@@ -543,7 +543,7 @@ JS_DEFINE_NATIVE_FUNCTION(GlobalObject::escape)
     auto string = TRY(vm.argument(0).to_utf16_string(vm));
 
     // 3. Let R be the empty String.
-    StringBuilder escaped;
+    StringBuilder escaped(StringBuilder::Mode::UTF16);
 
     // 4. Let unescapedSet be the string-concatenation of the ASCII word characters and "@*+-./".
     auto unescaped_set = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789@*_+-./"sv;
@@ -581,7 +581,7 @@ JS_DEFINE_NATIVE_FUNCTION(GlobalObject::escape)
     }
 
     // 7. Return R.
-    return PrimitiveString::create(vm, escaped.to_byte_string());
+    return PrimitiveString::create(vm, escaped.to_utf16_string());
 }
 
 // B.2.1.2 unescape ( string ), https://tc39.es/ecma262/#sec-unescape-string
@@ -598,7 +598,7 @@ JS_DEFINE_NATIVE_FUNCTION(GlobalObject::unescape)
 
     // 4. Let k be 0.
     // 5. Repeat, while k ≠ length,
-    for (auto k = 0; k < length; ++k) {
+    for (size_t k = 0; k < length; ++k) {
         // a. Let c be the code unit at index k within string.
         u16 code_unit = string.code_unit_at(k);
 
diff --git a/Libraries/LibJS/Runtime/Intl/AbstractOperations.cpp b/Libraries/LibJS/Runtime/Intl/AbstractOperations.cpp
index 81cf582036..ddf706c906 100644
--- a/Libraries/LibJS/Runtime/Intl/AbstractOperations.cpp
+++ b/Libraries/LibJS/Runtime/Intl/AbstractOperations.cpp
@@ -34,7 +34,7 @@ static bool is_well_formed_language_tag_impl(ViewType locale)
         quick_sort(variants);
 
         for (size_t i = 0; i < variants.size() - 1; ++i) {
-            if (variants[i].equals_ignoring_case(variants[i + 1]))
+            if (variants[i].equals_ignoring_ascii_case(variants[i + 1]))
                 return true;
         }
 
@@ -121,12 +121,12 @@ bool is_well_formed_language_tag(Utf16View locale)
 }
 
 // 6.2.2 CanonicalizeUnicodeLocaleId ( locale ), https://tc39.es/ecma402/#sec-canonicalizeunicodelocaleid
-String canonicalize_unicode_locale_id(StringView locale)
+Utf16String canonicalize_unicode_locale_id(StringView locale)
 {
     return Unicode::canonicalize_unicode_locale_id(locale);
 }
 
-String canonicalize_unicode_locale_id(Utf16View locale)
+Utf16String canonicalize_unicode_locale_id(Utf16View locale)
 {
     return Unicode::canonicalize_unicode_locale_id(locale);
 }
@@ -189,8 +189,8 @@ Vector<TimeZoneIdentifier> const& available_named_time_zone_identifiers()
             auto primary = identifier;
 
             // b. If identifier is a Link name and identifier is not "UTC", then
-            if (identifier != "UTC"sv) {
-                if (auto resolved = Unicode::resolve_primary_time_zone(identifier); resolved.has_value() && identifier != resolved) {
+            if (identifier.utf16_view() != "UTC"sv) {
+                if (auto resolved = Unicode::resolve_primary_time_zone(identifier.utf16_view().bytes()); resolved.has_value() && identifier != *resolved) {
                     // i. Set primary to the Zone name that identifier resolves to, according to the rules for resolving Link
                     //    names in the IANA Time Zone Database.
                     primary = resolved.release_value();
@@ -200,16 +200,19 @@ Vector<TimeZoneIdentifier> const& available_named_time_zone_identifiers()
             }
 
             // c. If primary is one of "Etc/UTC", "Etc/GMT", or "GMT", set primary to "UTC".
-            if (primary.is_one_of("Etc/UTC"sv, "Etc/GMT"sv, "GMT"sv))
-                primary = "UTC"_string;
+            if (primary.utf16_view().is_one_of("Etc/UTC"sv, "Etc/GMT"sv, "GMT"sv))
+                primary = "UTC"_utf16;
 
             // d. Let record be the Time Zone Identifier Record { [[Identifier]]: identifier, [[PrimaryIdentifier]]: primary }.
-            TimeZoneIdentifier record { .identifier = identifier, .primary_identifier = primary };
+            TimeZoneIdentifier record {
+                .identifier = identifier,
+                .primary_identifier = primary,
+            };
 
             // e. Append record to result.
             result.unchecked_append(move(record));
 
-            if (!found_utc && identifier == "UTC"sv && primary == "UTC"sv)
+            if (!found_utc && identifier.utf16_view() == "UTC"sv && primary.utf16_view() == "UTC"sv)
                 found_utc = true;
         }
 
@@ -224,7 +227,7 @@ Vector<TimeZoneIdentifier> const& available_named_time_zone_identifiers()
 }
 
 // 6.5.2 GetAvailableNamedTimeZoneIdentifier ( timeZoneIdentifier ), https://tc39.es/ecma402/#sec-getavailablenamedtimezoneidentifier
-Optional<TimeZoneIdentifier const&> get_available_named_time_zone_identifier(StringView time_zone_identifier)
+Optional<TimeZoneIdentifier const&> get_available_named_time_zone_identifier(Utf16View time_zone_identifier)
 {
     // 1. For each element record of AvailableNamedTimeZoneIdentifiers(), do
     for (auto const& record : available_named_time_zone_identifiers()) {
@@ -287,18 +290,18 @@ bool is_well_formed_unit_identifier(Utf16View unit_identifier)
 }
 
 // 9.2.1 CanonicalizeLocaleList ( locales ), https://tc39.es/ecma402/#sec-canonicalizelocalelist
-ThrowCompletionOr<Vector<String>> canonicalize_locale_list(VM& vm, Value locales)
+ThrowCompletionOr<Vector<Utf16String>> canonicalize_locale_list(VM& vm, Value locales)
 {
     auto& realm = *vm.current_realm();
 
     // 1. If locales is undefined, then
     if (locales.is_undefined()) {
         // a. Return a new empty List.
-        return Vector<String> {};
+        return Vector<Utf16String> {};
     }
 
     // 2. Let seen be a new empty List.
-    Vector<String> seen;
+    Vector<Utf16String> seen;
 
     Object* object = nullptr;
     // 3. If Type(locales) is String or Type(locales) is Object and locales has an [[InitializedLocale]] internal slot, then
@@ -334,12 +337,12 @@ ThrowCompletionOr<Vector<String>> canonicalize_locale_list(VM& vm, Value locales
             if (!key_value.is_string() && !key_value.is_object())
                 return vm.throw_completion<TypeError>(ErrorType::NotAnObjectOrString, key_value);
 
-            String canonicalized_tag;
+            Utf16String canonicalized_tag;
 
             // iii. If Type(kValue) is Object and kValue has an [[InitializedLocale]] internal slot, then
             if (auto locale = key_value.as_if<Locale>()) {
                 // 1. Let tag be kValue.[[Locale]].
-                auto tag = locale->locale();
+                auto tag = locale->locale().utf16_view();
 
                 // v. If IsWellFormedLanguageTag(tag) is false, throw a RangeError exception.
                 if (!is_well_formed_language_tag(tag))
@@ -374,17 +377,15 @@ ThrowCompletionOr<Vector<String>> canonicalize_locale_list(VM& vm, Value locales
 }
 
 // 9.2.3 LookupMatchingLocaleByPrefix ( availableLocales, requestedLocales ), https://tc39.es/ecma402/#sec-lookupmatchinglocalebyprefix
-Optional<MatchedLocale> lookup_matching_locale_by_prefix(ReadonlySpan<String> requested_locales)
+Optional<MatchedLocale> lookup_matching_locale_by_prefix(ReadonlySpan<Utf16String> requested_locales)
 {
     // 1. For each element locale of requestedLocales, do
     for (auto locale : requested_locales) {
-        auto locale_id = Unicode::parse_unicode_locale_id(locale);
+        auto locale_id = Unicode::parse_unicode_locale_id(locale.utf16_view());
         VERIFY(locale_id.has_value());
 
         // a. Let extension be empty.
         Optional<Unicode::Extension> extension;
-        String locale_without_extension;
-
         // b. If locale contains a Unicode locale extension sequence, then
         if (auto extensions = locale_id->remove_extension_type<Unicode::LocaleExtension>(); !extensions.is_empty()) {
             VERIFY(extensions.size() == 1);
@@ -393,24 +394,24 @@ Optional<MatchedLocale> lookup_matching_locale_by_prefix(ReadonlySpan<String> re
             extension = extensions.take_first();
 
             // ii. Set locale to the String value that is locale with any Unicode locale extension sequences removed.
-            locale = locale_id->to_string();
+            locale = locale_id->to_utf16_string();
         }
 
         // c. Let prefix be locale.
-        StringView prefix { locale };
+        auto prefix = locale.utf16_view();
 
         // d. Repeat, while prefix is not the empty String,
         while (!prefix.is_empty()) {
             // i. If availableLocales contains prefix, return the Record { [[locale]]: prefix, [[extension]]: extension }.
-            if (Unicode::is_locale_available(prefix))
-                return MatchedLocale { MUST(String::from_utf8(prefix)), move(extension) };
+            if (Unicode::is_locale_available(prefix.bytes()))
+                return MatchedLocale { Utf16String::from_utf16(prefix), move(extension) };
 
             // ii. If prefix contains "-" (code unit 0x002D HYPHEN-MINUS), let pos be the index into prefix of the last
             //     occurrence of "-"; else let pos be 0.
-            auto position = prefix.find_last('-').value_or(0);
+            auto position = prefix.find_last_code_point_offset('-').value_or(0);
 
             // iii. Repeat, while pos ≥ 2 and the substring of prefix from pos - 2 to pos - 1 is "-",
-            while (position >= 2 && prefix.substring_view(position - 2, 1) == '-') {
+            while (position >= 2 && prefix.substring_view(position - 2, 1) == "-"sv) {
                 // 1. Set pos to pos - 2.
                 position -= 2;
             }
@@ -425,7 +426,7 @@ Optional<MatchedLocale> lookup_matching_locale_by_prefix(ReadonlySpan<String> re
 }
 
 // 9.2.4 LookupMatchingLocaleByBestFit ( availableLocales, requestedLocales ), https://tc39.es/ecma402/#sec-lookupmatchinglocalebybestfit
-Optional<MatchedLocale> lookup_matching_locale_by_best_fit(ReadonlySpan<String> requested_locales)
+Optional<MatchedLocale> lookup_matching_locale_by_best_fit(ReadonlySpan<Utf16String> requested_locales)
 {
     // The algorithm is implementation dependent, but should produce results that a typical user of the requested locales
     // would consider at least as good as those produced by the LookupMatchingLocaleByPrefix algorithm.
@@ -433,7 +434,7 @@ Optional<MatchedLocale> lookup_matching_locale_by_best_fit(ReadonlySpan<String>
 }
 
 // 9.2.6 InsertUnicodeExtensionAndCanonicalize ( locale, attributes, keywords ), https://tc39.es/ecma402/#sec-insert-unicode-extension-and-canonicalize
-String insert_unicode_extension_and_canonicalize(Unicode::LocaleID locale, Vector<String> attributes, Vector<Unicode::Keyword> keywords)
+Utf16String insert_unicode_extension_and_canonicalize(Unicode::LocaleID locale, Vector<Utf16String> attributes, Vector<Unicode::Keyword> keywords)
 {
     // Note: This implementation differs from the spec in how the extension is inserted. The spec assumes
     // the input to this method is a string, and is written such that operations are performed on parts
@@ -442,11 +443,11 @@ String insert_unicode_extension_and_canonicalize(Unicode::LocaleID locale, Vecto
     locale.extensions.append(Unicode::LocaleExtension { move(attributes), move(keywords) });
 
     // 10. Return CanonicalizeUnicodeLocaleId(newLocale).
-    return JS::Intl::canonicalize_unicode_locale_id(locale.to_string());
+    return JS::Intl::canonicalize_unicode_locale_id(locale.to_utf16_string());
 }
 
 template<typename T>
-static auto& find_key_in_value(T& value, StringView key)
+static auto& find_key_in_value(T& value, Utf16View key)
 {
     if (key == "ca"sv)
         return value.ca;
@@ -465,7 +466,7 @@ static auto& find_key_in_value(T& value, StringView key)
     VERIFY_NOT_REACHED();
 }
 
-static Vector<LocaleKey> available_keyword_values(StringView locale, StringView key)
+static Vector<LocaleKey> available_keyword_values(Utf16View locale, Utf16View key)
 {
     auto key_locale_data = Unicode::available_keyword_values(locale, key);
 
@@ -485,9 +486,9 @@ static Vector<LocaleKey> available_keyword_values(StringView locale, StringView
 }
 
 // 9.2.7 ResolveLocale ( availableLocales, requestedLocales, options, relevantExtensionKeys, localeData ), https://tc39.es/ecma402/#sec-resolvelocale
-ResolvedLocale resolve_locale(ReadonlySpan<String> requested_locales, LocaleOptions const& options, ReadonlySpan<StringView> relevant_extension_keys)
+ResolvedLocale resolve_locale(ReadonlySpan<Utf16String> requested_locales, LocaleOptions const& options, ReadonlySpan<Utf16View> relevant_extension_keys)
 {
-    static auto true_string = "true"_string;
+    auto true_string = "true"_utf16;
 
     // 1. Let matcher be options.[[localeMatcher]].
     auto const& matcher = options.locale_matcher;
@@ -507,7 +508,7 @@ ResolvedLocale resolve_locale(ReadonlySpan<String> requested_locales, LocaleOpti
 
     // 4. If r is undefined, set r to the Record { [[locale]]: DefaultLocale(), [[extension]]: empty }.
     if (!matcher_result.has_value())
-        matcher_result = MatchedLocale { MUST(String::from_utf8(Unicode::default_locale())), {} };
+        matcher_result = MatchedLocale { Utf16String::from_utf16(Unicode::default_locale()), {} };
 
     // 5. Let foundLocale be r.[[locale]].
     auto found_locale = move(matcher_result->locale);
@@ -541,7 +542,7 @@ ResolvedLocale resolve_locale(ReadonlySpan<String> requested_locales, LocaleOpti
     for (auto const& key : relevant_extension_keys) {
         // a. Let keyLocaleData be foundLocaleData.[[<key>]].
         // b. Assert: keyLocaleData is a List.
-        auto key_locale_data = available_keyword_values(found_locale, key);
+        auto key_locale_data = available_keyword_values(found_locale.utf16_view(), key);
 
         // c. Let value be keyLocaleData[0].
         // d. Assert: value is a String or value is null.
@@ -551,7 +552,7 @@ ResolvedLocale resolve_locale(ReadonlySpan<String> requested_locales, LocaleOpti
         Optional<Unicode::Keyword> supported_keyword;
 
         // f. If keywords contains an element whose [[Key]] is key, then
-        if (auto entry = keywords.find_if([&](auto const& entry) { return entry.key == key; }); entry != keywords.end()) {
+        if (auto entry = keywords.find_if([&](auto const& entry) { return entry.key.utf16_view() == key; }); entry != keywords.end()) {
             // i. Let entry be the element of keywords whose [[Key]] is key.
             // ii. Let requestedValue be entry.[[Value]].
             auto requested_value = entry->value;
@@ -564,7 +565,7 @@ ResolvedLocale resolve_locale(ReadonlySpan<String> requested_locales, LocaleOpti
                     value = move(requested_value);
 
                     // b. Set supportedKeyword to the Record { [[Key]]: key, [[Value]]: value }.
-                    supported_keyword = Unicode::Keyword { MUST(String::from_utf8(key)), move(entry->value) };
+                    supported_keyword = Unicode::Keyword { Utf16String::from_utf16(key), move(entry->value) };
                 }
             }
             // iv. Else if keyLocaleData contains "true", then
@@ -573,7 +574,7 @@ ResolvedLocale resolve_locale(ReadonlySpan<String> requested_locales, LocaleOpti
                 value = true_string;
 
                 // 2. Set supportedKeyword to the Record { [[Key]]: key, [[Value]]: "" }.
-                supported_keyword = Unicode::Keyword { MUST(String::from_utf8(key)), {} };
+                supported_keyword = Unicode::Keyword { Utf16String::from_utf16(key), {} };
             }
         }
 
@@ -583,13 +584,14 @@ ResolvedLocale resolve_locale(ReadonlySpan<String> requested_locales, LocaleOpti
         auto options_value = find_key_in_value(options, key);
 
         // j. If optionsValue is a String, then
-        if (auto* options_string = options_value.has_value() ? options_value->get_pointer<String>() : nullptr) {
+        if (auto* options_string = options_value.has_value() ? options_value->get_pointer<Utf16String>() : nullptr) {
             // i. Let ukey be the ASCII-lowercase of key.
             // NOTE: `key` is always lowercase, and this step is likely to be removed:
             //        https://github.com/tc39/ecma402/pull/846#discussion_r1428263375
 
             // ii. Set optionsValue to CanonicalizeUValue(ukey, optionsValue).
-            *options_string = Unicode::canonicalize_unicode_extension_values(key, *options_string);
+            auto canonicalized = Unicode::canonicalize_unicode_extension_values(key.bytes(), options_string->utf16_view());
+            *options_string = move(canonicalized);
 
             // iii. If optionsValue is the empty String, then
             if (options_string->is_empty()) {
@@ -611,31 +613,36 @@ ResolvedLocale resolve_locale(ReadonlySpan<String> requested_locales, LocaleOpti
         if (supported_keyword.has_value())
             supported_keywords.append(supported_keyword.release_value());
 
-        if (auto* value_string = value.get_pointer<String>())
-            icu_keywords.empend(MUST(String::from_utf8(key)), *value_string);
+        if (auto* value_string = value.get_pointer<Utf16String>())
+            icu_keywords.empend(Utf16String::from_utf16(key), *value_string);
 
         // m. Set result.[[<key>]] to value.
-        find_key_in_value(result, key) = move(value);
+        if (auto* value_string = value.get_pointer<Utf16String>())
+            find_key_in_value(result, key) = *value_string;
+        else
+            find_key_in_value(result, key) = Empty {};
     }
 
     // AD-HOC: For ICU, we need to form a locale with all relevant extension keys present.
     if (icu_keywords.is_empty()) {
         result.icu_locale = found_locale;
     } else {
-        auto locale_id = Unicode::parse_unicode_locale_id(found_locale);
+        auto locale_id = Unicode::parse_unicode_locale_id(found_locale.utf16_view());
         VERIFY(locale_id.has_value());
 
-        result.icu_locale = insert_unicode_extension_and_canonicalize(locale_id.release_value(), {}, move(icu_keywords));
+        auto icu_locale = insert_unicode_extension_and_canonicalize(locale_id.release_value(), {}, move(icu_keywords));
+        result.icu_locale = move(icu_locale);
     }
 
     // 14. If supportedKeywords is not empty, then
     if (!supported_keywords.is_empty()) {
-        auto locale_id = Unicode::parse_unicode_locale_id(found_locale);
+        auto locale_id = Unicode::parse_unicode_locale_id(found_locale.utf16_view());
         VERIFY(locale_id.has_value());
 
         // a. Let supportedAttributes be a new empty List.
         // b. Set foundLocale to InsertUnicodeExtensionAndCanonicalize(foundLocale, supportedAttributes, supportedKeywords).
-        found_locale = insert_unicode_extension_and_canonicalize(locale_id.release_value(), {}, move(supported_keywords));
+        auto supported_locale = insert_unicode_extension_and_canonicalize(locale_id.release_value(), {}, move(supported_keywords));
+        found_locale = move(supported_locale);
     }
 
     // 15. Set result.[[Locale]] to foundLocale.
@@ -662,7 +669,7 @@ ThrowCompletionOr<ResolvedOptions> resolve_options(VM& vm, IntlObject& object, V
         : TRY(get_options_object(vm, options_value));
 
     // 4. Let matcher be ? GetOption(options, "localeMatcher", STRING, « "lookup", "best fit" », "best fit").
-    auto matcher = TRY(get_option(vm, options, vm.names.localeMatcher, OptionType::String, { "lookup"sv, "best fit"sv }, "best fit"sv));
+    auto matcher = TRY(get_option(vm, options, vm.names.localeMatcher, OptionType::String, { "lookup"sv, "best fit"sv }, u"best fit"sv));
 
     // 5. Let opt be the Record { [[localeMatcher]]: matcher }.
     LocaleOptions opt {};
@@ -687,10 +694,10 @@ ThrowCompletionOr<ResolvedOptions> resolve_options(VM& vm, IntlObject& object, V
             auto value_string_view = value_string.utf16_view();
 
             // ii. If value cannot be matched by the type Unicode locale nonterminal, throw a RangeError exception.
-            if (!value_string_view.is_ascii() || !Unicode::is_type_identifier(value_string_view))
+            if (!value_string_view.has_ascii_storage() || !Unicode::is_type_identifier(value_string_view))
                 return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, value_string_view, descriptor.property);
 
-            locale_key = MUST(value_string_view.to_utf8());
+            locale_key = move(value_string);
         }
 
         // e. Let key be desc.[[Key]].
@@ -715,7 +722,7 @@ ThrowCompletionOr<ResolvedOptions> resolve_options(VM& vm, IntlObject& object, V
 }
 
 // 9.2.9 FilterLocales ( availableLocales, requestedLocales, options ), https://tc39.es/ecma402/#sec-lookupsupportedlocales
-ThrowCompletionOr<GC::Ref<Array>> filter_locales(VM& vm, ReadonlySpan<String> requested_locales, Value options_value)
+ThrowCompletionOr<GC::Ref<Array>> filter_locales(VM& vm, ReadonlySpan<Utf16String> requested_locales, Value options_value)
 {
     auto& realm = *vm.current_realm();
 
@@ -723,10 +730,10 @@ ThrowCompletionOr<GC::Ref<Array>> filter_locales(VM& vm, ReadonlySpan<String> re
     auto options = TRY(coerce_options_to_object(vm, options_value));
 
     // 2. Let matcher be ? GetOption(options, "localeMatcher", string, « "lookup", "best fit" », "best fit").
-    auto matcher = TRY(get_option(vm, options, vm.names.localeMatcher, OptionType::String, { "lookup"sv, "best fit"sv }, "best fit"sv));
+    auto matcher = TRY(get_option(vm, options, vm.names.localeMatcher, OptionType::String, { "lookup"sv, "best fit"sv }, u"best fit"sv));
 
     // 3. Let subset be a new empty List.
-    Vector<String> subset;
+    Vector<Utf16String> subset;
 
     // 4. For each element locale of requestedLocales, do
     for (auto const& locale : requested_locales) {
@@ -749,7 +756,7 @@ ThrowCompletionOr<GC::Ref<Array>> filter_locales(VM& vm, ReadonlySpan<String> re
     }
 
     // 5. Return CreateArrayFromList(subset).
-    return Array::create_from<String>(realm, subset, [&vm](auto& locale) { return PrimitiveString::create(vm, move(locale)); });
+    return Array::create_from<Utf16String>(realm, subset, [&vm](auto const& locale) { return PrimitiveString::create(vm, locale); });
 }
 
 // 9.2.11 CoerceOptionsToObject ( options ), https://tc39.es/ecma402/#sec-coerceoptionstoobject
diff --git a/Libraries/LibJS/Runtime/Intl/AbstractOperations.h b/Libraries/LibJS/Runtime/Intl/AbstractOperations.h
index 25b2377408..f11678183e 100644
--- a/Libraries/LibJS/Runtime/Intl/AbstractOperations.h
+++ b/Libraries/LibJS/Runtime/Intl/AbstractOperations.h
@@ -9,6 +9,7 @@
 #include <AK/EnumBits.h>
 #include <AK/Span.h>
 #include <AK/String.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 #include <AK/Variant.h>
 #include <AK/Vector.h>
@@ -20,7 +21,8 @@
 
 namespace JS::Intl {
 
-using LocaleKey = Variant<Empty, String>;
+using LocaleKey = Variant<Empty, Utf16String>;
+using ResolvedLocaleKey = Variant<Empty, Utf16String>;
 
 struct LocaleOptions {
     Value locale_matcher;
@@ -34,19 +36,19 @@ struct LocaleOptions {
 };
 
 struct MatchedLocale {
-    String locale;
+    Utf16String locale;
     Optional<Unicode::Extension> extension;
 };
 
 struct ResolvedLocale {
-    String locale;
-    String icu_locale;
-    LocaleKey ca; // [[Calendar]]
-    LocaleKey co; // [[Collation]]
-    LocaleKey hc; // [[HourCycle]]
-    LocaleKey kf; // [[CaseFirst]]
-    LocaleKey kn; // [[Numeric]]
-    LocaleKey nu; // [[NumberingSystem]]
+    Utf16String locale;
+    Utf16String icu_locale;
+    ResolvedLocaleKey ca; // [[Calendar]]
+    ResolvedLocaleKey co; // [[Collation]]
+    ResolvedLocaleKey hc; // [[HourCycle]]
+    ResolvedLocaleKey kf; // [[CaseFirst]]
+    ResolvedLocaleKey kn; // [[Numeric]]
+    ResolvedLocaleKey nu; // [[NumberingSystem]]
 };
 
 struct ResolvedOptions {
@@ -66,20 +68,20 @@ using StringOrBoolean = Variant<StringView, bool>;
 
 bool is_well_formed_language_tag(StringView locale);
 bool is_well_formed_language_tag(Utf16View locale);
-String canonicalize_unicode_locale_id(StringView locale);
-String canonicalize_unicode_locale_id(Utf16View locale);
+Utf16String canonicalize_unicode_locale_id(StringView locale);
+Utf16String canonicalize_unicode_locale_id(Utf16View locale);
 bool is_well_formed_currency_code(StringView currency);
 bool is_well_formed_currency_code(Utf16View currency);
 Vector<TimeZoneIdentifier> const& available_named_time_zone_identifiers();
-Optional<TimeZoneIdentifier const&> get_available_named_time_zone_identifier(StringView time_zone_identifier);
+Optional<TimeZoneIdentifier const&> get_available_named_time_zone_identifier(Utf16View time_zone_identifier);
 bool is_well_formed_unit_identifier(Utf16View unit_identifier);
-ThrowCompletionOr<Vector<String>> canonicalize_locale_list(VM&, Value locales);
-Optional<MatchedLocale> lookup_matching_locale_by_prefix(ReadonlySpan<String> requested_locales);
-Optional<MatchedLocale> lookup_matching_locale_by_best_fit(ReadonlySpan<String> requested_locales);
-String insert_unicode_extension_and_canonicalize(Unicode::LocaleID locale_id, Vector<String> attributes, Vector<Unicode::Keyword> keywords);
-ResolvedLocale resolve_locale(ReadonlySpan<String> requested_locales, LocaleOptions const& options, ReadonlySpan<StringView> relevant_extension_keys);
+ThrowCompletionOr<Vector<Utf16String>> canonicalize_locale_list(VM&, Value locales);
+Optional<MatchedLocale> lookup_matching_locale_by_prefix(ReadonlySpan<Utf16String> requested_locales);
+Optional<MatchedLocale> lookup_matching_locale_by_best_fit(ReadonlySpan<Utf16String> requested_locales);
+Utf16String insert_unicode_extension_and_canonicalize(Unicode::LocaleID locale_id, Vector<Utf16String> attributes, Vector<Unicode::Keyword> keywords);
+ResolvedLocale resolve_locale(ReadonlySpan<Utf16String> requested_locales, LocaleOptions const& options, ReadonlySpan<Utf16View> relevant_extension_keys);
 ThrowCompletionOr<ResolvedOptions> resolve_options(VM& vm, IntlObject& object, Value locales, Value options_value, SpecialBehaviors special_behaviours = SpecialBehaviors::None, Function<void(LocaleOptions&)> modify_resolution_options = {});
-ThrowCompletionOr<GC::Ref<Array>> filter_locales(VM& vm, ReadonlySpan<String> requested_locales, Value options);
+ThrowCompletionOr<GC::Ref<Array>> filter_locales(VM& vm, ReadonlySpan<Utf16String> requested_locales, Value options);
 ThrowCompletionOr<GC::Ref<Object>> coerce_options_to_object(VM&, Value options);
 ThrowCompletionOr<StringOrBoolean> get_boolean_or_string_number_format_option(VM& vm, Object const& options, PropertyKey const& property, ReadonlySpan<StringView> string_values, StringOrBoolean fallback);
 ThrowCompletionOr<Optional<int>> default_number_option(VM&, Value value, int minimum, int maximum, Optional<int> fallback);
diff --git a/Libraries/LibJS/Runtime/Intl/Collator.cpp b/Libraries/LibJS/Runtime/Intl/Collator.cpp
index 04905180e7..e5a2c52e3a 100644
--- a/Libraries/LibJS/Runtime/Intl/Collator.cpp
+++ b/Libraries/LibJS/Runtime/Intl/Collator.cpp
@@ -24,10 +24,10 @@ void Collator::visit_edges(Visitor& visitor)
 }
 
 // 10.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl-collator-internal-slots
-ReadonlySpan<StringView> Collator::relevant_extension_keys() const
+ReadonlySpan<Utf16View> Collator::relevant_extension_keys() const
 {
     // The value of the [[RelevantExtensionKeys]] internal slot is a List that must include the element "co", may include any or all of the elements "kf" and "kn", and must not include any other elements.
-    static constexpr AK::Array keys { "co"sv, "kf"sv, "kn"sv };
+    static constexpr AK::Array<Utf16View, 3> keys { "co"sv, "kf"sv, "kn"sv };
     return keys;
 }
 
diff --git a/Libraries/LibJS/Runtime/Intl/Collator.h b/Libraries/LibJS/Runtime/Intl/Collator.h
index 6b397faaac..6c02f70fa7 100644
--- a/Libraries/LibJS/Runtime/Intl/Collator.h
+++ b/Libraries/LibJS/Runtime/Intl/Collator.h
@@ -8,6 +8,7 @@
 
 #include <AK/String.h>
 #include <AK/StringView.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 #include <LibJS/Runtime/Intl/CollatorCompareFunction.h>
 #include <LibJS/Runtime/Intl/IntlObject.h>
@@ -22,26 +23,26 @@ class Collator final : public IntlObject {
 public:
     virtual ~Collator() override = default;
 
-    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<Utf16View> relevant_extension_keys() const override;
     virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
 
-    String const& locale() const { return m_locale; }
-    void set_locale(String locale) { m_locale = move(locale); }
+    Utf16String const& locale() const { return m_locale; }
+    void set_locale(Utf16String locale) { m_locale = move(locale); }
 
     Unicode::Usage usage() const { return m_usage; }
     void set_usage(Utf16View usage) { m_usage = Unicode::usage_from_string(usage); }
-    StringView usage_string() const LIFETIME_BOUND { return Unicode::usage_to_string(m_usage); }
+    Utf16String usage_string() const { return Unicode::usage_to_string(m_usage); }
 
     Unicode::Sensitivity sensitivity() const { return m_sensitivity; }
     void set_sensitivity(Unicode::Sensitivity sensitivity) { m_sensitivity = sensitivity; }
-    StringView sensitivity_string() const LIFETIME_BOUND { return Unicode::sensitivity_to_string(m_sensitivity); }
+    Utf16String sensitivity_string() const { return Unicode::sensitivity_to_string(m_sensitivity); }
 
     Unicode::CaseFirst case_first() const { return m_case_first; }
-    void set_case_first(StringView case_first) { m_case_first = Unicode::case_first_from_string(case_first); }
-    StringView case_first_string() const LIFETIME_BOUND { return Unicode::case_first_to_string(m_case_first); }
+    void set_case_first(Utf16View case_first) { m_case_first = Unicode::case_first_from_string(case_first); }
+    Utf16String case_first_string() const { return Unicode::case_first_to_string(m_case_first); }
 
-    String const& collation() const { return m_collation; }
-    void set_collation(String collation) { m_collation = move(collation); }
+    Utf16String const& collation() const { return m_collation; }
+    void set_collation(Utf16String collation) { m_collation = move(collation); }
 
     bool ignore_punctuation() const { return m_ignore_punctuation; }
     void set_ignore_punctuation(bool ignore_punctuation) { m_ignore_punctuation = ignore_punctuation; }
@@ -60,11 +61,11 @@ private:
 
     virtual void visit_edges(Visitor&) override;
 
-    String m_locale;                                                      // [[Locale]]
+    Utf16String m_locale;                                                 // [[Locale]]
     Unicode::Usage m_usage { Unicode::Usage::Sort };                      // [[Usage]]
     Unicode::Sensitivity m_sensitivity { Unicode::Sensitivity::Variant }; // [[Sensitivity]]
     Unicode::CaseFirst m_case_first { Unicode::CaseFirst::False };        // [[CaseFirst]]
-    String m_collation;                                                   // [[Collation]]
+    Utf16String m_collation;                                              // [[Collation]]
     bool m_ignore_punctuation { false };                                  // [[IgnorePunctuation]]
     bool m_numeric { false };                                             // [[Numeric]]
     GC::Ptr<CollatorCompareFunction> m_bound_compare;                     // [[BoundCompare]]
diff --git a/Libraries/LibJS/Runtime/Intl/CollatorCompareFunction.cpp b/Libraries/LibJS/Runtime/Intl/CollatorCompareFunction.cpp
index 48d5cec5c3..ae2309cfac 100644
--- a/Libraries/LibJS/Runtime/Intl/CollatorCompareFunction.cpp
+++ b/Libraries/LibJS/Runtime/Intl/CollatorCompareFunction.cpp
@@ -28,7 +28,7 @@ void CollatorCompareFunction::initialize(Realm& realm)
     Base::initialize(realm);
     auto& vm = this->vm();
     define_direct_property(vm.names.length, Value(2), Attribute::Configurable);
-    define_direct_property(vm.names.name, PrimitiveString::create(vm, String {}), Attribute::Configurable);
+    define_direct_property(vm.names.name, PrimitiveString::create(vm, Utf16String {}), Attribute::Configurable);
 }
 
 void CollatorCompareFunction::visit_edges(Visitor& visitor)
diff --git a/Libraries/LibJS/Runtime/Intl/CollatorConstructor.cpp b/Libraries/LibJS/Runtime/Intl/CollatorConstructor.cpp
index ff3b281068..71ac2425bc 100644
--- a/Libraries/LibJS/Runtime/Intl/CollatorConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Intl/CollatorConstructor.cpp
@@ -66,7 +66,7 @@ ThrowCompletionOr<GC::Ref<Object>> CollatorConstructor::construct(FunctionObject
     auto options = TRY(coerce_options_to_object(vm, options_value));
 
     // 7. Let usage be ? GetOption(options, "usage", string, « "sort", "search" », "sort").
-    auto usage = TRY(get_option(vm, options, vm.names.usage, OptionType::String, { "sort"sv, "search"sv }, "sort"sv));
+    auto usage = TRY(get_option(vm, options, vm.names.usage, OptionType::String, { "sort"sv, "search"sv }, u"sort"sv));
 
     // 8. Set collator.[[Usage]] to usage.
     collator->set_usage(usage.as_string().utf16_string_view());
@@ -77,7 +77,7 @@ ThrowCompletionOr<GC::Ref<Object>> CollatorConstructor::construct(FunctionObject
     //     a. Let localeData be %Intl.Collator%.[[SearchLocaleData]].
 
     // 11. Let optionsResolution be ? ResolveOptions(%Intl.Collator%, localeData, CreateArrayFromList(requestedLocales), options).
-    auto requested_locales_array = Array::create_from<String>(realm, requested_locales, [&](auto& locale) { return PrimitiveString::create(vm, move(locale)); });
+    auto requested_locales_array = Array::create_from<Utf16String>(realm, requested_locales, [&](auto const& locale) { return PrimitiveString::create(vm, locale); });
     auto options_resolution = TRY(resolve_options(vm, collator, requested_locales_array, options_value));
 
     // 12. Let r be optionsResolution.[[ResolvedLocale]].
@@ -88,25 +88,25 @@ ThrowCompletionOr<GC::Ref<Object>> CollatorConstructor::construct(FunctionObject
 
     // 14. If r.[[co]] is null, let collation be "default". Otherwise, let collation be r.[[co]].
     auto collation = result.co.has<Empty>()
-        ? "default"_string
-        : move(result.co.get<String>());
+        ? "default"_utf16
+        : move(result.co.get<Utf16String>());
 
     // 15. Set collator.[[Collation]] to collation.
     collator->set_collation(move(collation));
 
     // 16. Set collator.[[Numeric]] to SameValue(r.[[kn]], "true").
-    collator->set_numeric(result.kn == "true"_string);
+    collator->set_numeric(result.kn.has<Utf16String>() && result.kn.get<Utf16String>().utf16_view() == "true"sv);
 
     // 17. Set collator.[[CaseFirst]] to r.[[kf]].
-    if (auto const* resolved_case_first = result.kf.get_pointer<String>())
-        collator->set_case_first(*resolved_case_first);
+    if (auto const* resolved_case_first = result.kf.get_pointer<Utf16String>())
+        collator->set_case_first(resolved_case_first->utf16_view());
 
     // 18. Let resolvedLocaleData be r.[[LocaleData]].
 
     // 19. If usage is "sort", let defaultSensitivity be "variant". Otherwise, let defaultSensitivity be resolvedLocaleData.[[sensitivity]].
     // NOTE: We do not acquire resolvedLocaleData.[[sensitivity]] here. Instead, we let LibUnicode fill in the
     //       default value if an override was not provided here.
-    auto default_sensitivity = collator->usage() == Unicode::Usage::Sort ? "variant"sv : OptionDefault {};
+    auto default_sensitivity = collator->usage() == Unicode::Usage::Sort ? OptionDefault { u"variant"sv } : OptionDefault {};
 
     // 20. Set collator.[[Sensitivity]] to ? GetOption(options, "sensitivity", string, « "base", "accent", "case", "variant" », defaultSensitivity).
     auto sensitivity_value = TRY(get_option(vm, options, vm.names.sensitivity, OptionType::String, { "base"sv, "accent"sv, "case"sv, "variant"sv }, default_sensitivity));
@@ -128,9 +128,9 @@ ThrowCompletionOr<GC::Ref<Object>> CollatorConstructor::construct(FunctionObject
 
     // Non-standard, create an ICU collator for this Intl object.
     auto icu_collator = Unicode::Collator::create(
-        collator->locale(),
+        result.icu_locale.utf16_view().bytes(),
         collator->usage(),
-        collator->collation(),
+        collator->collation().utf16_view().bytes(),
         sensitivity,
         collator->case_first(),
         collator->numeric(),
diff --git a/Libraries/LibJS/Runtime/Intl/CollatorPrototype.cpp b/Libraries/LibJS/Runtime/Intl/CollatorPrototype.cpp
index f1a194252f..2d7d225efd 100644
--- a/Libraries/LibJS/Runtime/Intl/CollatorPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Intl/CollatorPrototype.cpp
@@ -26,7 +26,7 @@ void CollatorPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 10.3.4 Intl.Collator.prototype [ %Symbol.toStringTag% ], https://tc39.es/ecma402/#sec-intl.collator.prototype-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.Collator"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.Collator"_utf16_fly_string), Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(realm, vm.names.resolvedOptions, resolved_options, 0, attr);
diff --git a/Libraries/LibJS/Runtime/Intl/DateTimeFormat.cpp b/Libraries/LibJS/Runtime/Intl/DateTimeFormat.cpp
index d719f85645..cad7ac93b4 100644
--- a/Libraries/LibJS/Runtime/Intl/DateTimeFormat.cpp
+++ b/Libraries/LibJS/Runtime/Intl/DateTimeFormat.cpp
@@ -36,10 +36,10 @@ void DateTimeFormat::visit_edges(Cell::Visitor& visitor)
 }
 
 // 11.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl.datetimeformat-internal-slots
-ReadonlySpan<StringView> DateTimeFormat::relevant_extension_keys() const
+ReadonlySpan<Utf16View> DateTimeFormat::relevant_extension_keys() const
 {
     // The value of the [[RelevantExtensionKeys]] internal slot is « "ca", "hc", "nu" ».
-    static constexpr AK::Array keys { "ca"sv, "hc"sv, "nu"sv };
+    static constexpr AK::Array<Utf16View, 3> keys { "ca"sv, "hc"sv, "nu"sv };
     return keys;
 }
 
@@ -75,32 +75,32 @@ static Optional<Unicode::DateTimeFormat const&> get_or_create_formatter(StringVi
 
 Optional<Unicode::DateTimeFormat const&> DateTimeFormat::temporal_plain_date_formatter()
 {
-    return get_or_create_formatter(m_icu_locale, "GMT+00:00"sv, m_temporal_plain_date_formatter, m_temporal_plain_date_format);
+    return get_or_create_formatter(m_icu_locale.utf16_view().bytes(), "GMT+00:00"sv, m_temporal_plain_date_formatter, m_temporal_plain_date_format);
 }
 
 Optional<Unicode::DateTimeFormat const&> DateTimeFormat::temporal_plain_year_month_formatter()
 {
-    return get_or_create_formatter(m_icu_locale, "GMT+00:00"sv, m_temporal_plain_year_month_formatter, m_temporal_plain_year_month_format);
+    return get_or_create_formatter(m_icu_locale.utf16_view().bytes(), "GMT+00:00"sv, m_temporal_plain_year_month_formatter, m_temporal_plain_year_month_format);
 }
 
 Optional<Unicode::DateTimeFormat const&> DateTimeFormat::temporal_plain_month_day_formatter()
 {
-    return get_or_create_formatter(m_icu_locale, "GMT+00:00"sv, m_temporal_plain_month_day_formatter, m_temporal_plain_month_day_format);
+    return get_or_create_formatter(m_icu_locale.utf16_view().bytes(), "GMT+00:00"sv, m_temporal_plain_month_day_formatter, m_temporal_plain_month_day_format);
 }
 
 Optional<Unicode::DateTimeFormat const&> DateTimeFormat::temporal_plain_time_formatter()
 {
-    return get_or_create_formatter(m_icu_locale, "GMT+00:00"sv, m_temporal_plain_time_formatter, m_temporal_plain_time_format);
+    return get_or_create_formatter(m_icu_locale.utf16_view().bytes(), "GMT+00:00"sv, m_temporal_plain_time_formatter, m_temporal_plain_time_format);
 }
 
 Optional<Unicode::DateTimeFormat const&> DateTimeFormat::temporal_plain_date_time_formatter()
 {
-    return get_or_create_formatter(m_icu_locale, "GMT+00:00"sv, m_temporal_plain_date_time_formatter, m_temporal_plain_date_time_format);
+    return get_or_create_formatter(m_icu_locale.utf16_view().bytes(), "GMT+00:00"sv, m_temporal_plain_date_time_formatter, m_temporal_plain_date_time_format);
 }
 
 Optional<Unicode::DateTimeFormat const&> DateTimeFormat::temporal_instant_formatter()
 {
-    return get_or_create_formatter(m_icu_locale, m_temporal_time_zone, m_temporal_instant_formatter, m_temporal_instant_format);
+    return get_or_create_formatter(m_icu_locale.utf16_view().bytes(), m_temporal_time_zone.utf16_view().bytes(), m_temporal_instant_formatter, m_temporal_instant_format);
 }
 
 // 11.5.5 FormatDateTimePattern ( dateTimeFormat, patternParts, x, rangeFormatOptions ), https://tc39.es/ecma402/#sec-formatdatetimepattern
@@ -162,7 +162,7 @@ ThrowCompletionOr<GC::Ref<Array>> format_date_time_to_parts(VM& vm, DateTimeForm
         auto object = Object::create(realm, realm.intrinsics().object_prototype());
 
         // b. Perform ! CreateDataPropertyOrThrow(O, "type", part.[[Type]]).
-        MUST(object->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, part.type)));
+        MUST(object->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, move(part.type))));
 
         // c. Perform ! CreateDataPropertyOrThrow(O, "value", part.[[Value]]).
         MUST(object->create_data_property_or_throw(vm.names.value, PrimitiveString::create(vm, move(part.value))));
@@ -249,13 +249,13 @@ ThrowCompletionOr<GC::Ref<Array>> format_date_time_range_to_parts(VM& vm, DateTi
         auto object = Object::create(realm, realm.intrinsics().object_prototype());
 
         // b. Perform ! CreateDataPropertyOrThrow(O, "type", part.[[Type]]).
-        MUST(object->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, part.type)));
+        MUST(object->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, move(part.type))));
 
         // c. Perform ! CreateDataPropertyOrThrow(O, "value", part.[[Value]]).
         MUST(object->create_data_property_or_throw(vm.names.value, PrimitiveString::create(vm, move(part.value))));
 
         // d. Perform ! CreateDataPropertyOrThrow(O, "source", part.[[Source]]).
-        MUST(object->create_data_property_or_throw(vm.names.source, PrimitiveString::create(vm, part.source)));
+        MUST(object->create_data_property_or_throw(vm.names.source, PrimitiveString::create(vm, move(part.source))));
 
         // e. Perform ! CreateDataProperty(result, ! ToString(n), O).
         MUST(result->create_data_property_or_throw(n, object));
@@ -535,7 +535,8 @@ static double to_epoch_milliseconds(Crypto::SignedBigInteger const& epoch_nanose
 ThrowCompletionOr<ValueFormat> handle_date_time_temporal_date(VM& vm, DateTimeFormat& date_time_format, Temporal::PlainDate const& temporal_date)
 {
     // 1. If temporalDate.[[Calendar]] is not either dateTimeFormat.[[Calendar]] or "iso8601", throw a RangeError exception.
-    if (!temporal_date.calendar().is_one_of(date_time_format.calendar(), "iso8601"sv))
+    auto date_time_format_calendar = date_time_format.calendar().utf16_view().bytes();
+    if (!temporal_date.calendar().is_one_of(date_time_format_calendar, "iso8601"sv))
         return vm.throw_completion<RangeError>(ErrorType::IntlTemporalInvalidCalendar, "Temporal.PlainDate"sv, temporal_date.calendar(), date_time_format.calendar());
 
     // 2. Let isoDateTime be CombineISODateAndTimeRecord(temporalDate.[[ISODate]], NoonTimeRecord()).
@@ -559,7 +560,7 @@ ThrowCompletionOr<ValueFormat> handle_date_time_temporal_date(VM& vm, DateTimeFo
 ThrowCompletionOr<ValueFormat> handle_date_time_temporal_year_month(VM& vm, DateTimeFormat& date_time_format, Temporal::PlainYearMonth const& temporal_year_month)
 {
     // 1. If temporalYearMonth.[[Calendar]] is not equal to dateTimeFormat.[[Calendar]], throw a RangeError exception.
-    if (temporal_year_month.calendar() != date_time_format.calendar())
+    if (temporal_year_month.calendar() != date_time_format.calendar().utf16_view().bytes())
         return vm.throw_completion<RangeError>(ErrorType::IntlTemporalInvalidCalendar, "Temporal.PlainYearMonth"sv, temporal_year_month.calendar(), date_time_format.calendar());
 
     // 2. Let isoDateTime be CombineISODateAndTimeRecord(temporalYearMonth.[[ISODate]], NoonTimeRecord()).
@@ -583,7 +584,7 @@ ThrowCompletionOr<ValueFormat> handle_date_time_temporal_year_month(VM& vm, Date
 ThrowCompletionOr<ValueFormat> handle_date_time_temporal_month_day(VM& vm, DateTimeFormat& date_time_format, Temporal::PlainMonthDay const& temporal_month_day)
 {
     // 1. If temporalMonthDay.[[Calendar]] is not equal to dateTimeFormat.[[Calendar]], throw a RangeError exception.
-    if (temporal_month_day.calendar() != date_time_format.calendar())
+    if (temporal_month_day.calendar() != date_time_format.calendar().utf16_view().bytes())
         return vm.throw_completion<RangeError>(ErrorType::IntlTemporalInvalidCalendar, "Temporal.PlainMonthDay"sv, temporal_month_day.calendar(), date_time_format.calendar());
 
     // 2. Let isoDateTime be CombineISODateAndTimeRecord(temporalMonthDay.[[ISODate]], NoonTimeRecord()).
@@ -630,7 +631,8 @@ ThrowCompletionOr<ValueFormat> handle_date_time_temporal_time(VM& vm, DateTimeFo
 ThrowCompletionOr<ValueFormat> handle_date_time_temporal_date_time(VM& vm, DateTimeFormat& date_time_format, Temporal::PlainDateTime const& date_time)
 {
     // 1. If dateTime.[[Calendar]] is not "iso8601" and not equal to dateTimeFormat.[[Calendar]], throw a RangeError exception.
-    if (!date_time.calendar().is_one_of(date_time_format.calendar(), "iso8601"sv))
+    auto date_time_format_calendar = date_time_format.calendar().utf16_view().bytes();
+    if (!date_time.calendar().is_one_of(date_time_format_calendar, "iso8601"sv))
         return vm.throw_completion<RangeError>(ErrorType::IntlTemporalInvalidCalendar, "Temporal.PlainDateTime"sv, date_time.calendar(), date_time_format.calendar());
 
     // 2. Let epochNs be GetUTCEpochNanoseconds(dateTime.[[ISODateTime]]).
diff --git a/Libraries/LibJS/Runtime/Intl/DateTimeFormat.h b/Libraries/LibJS/Runtime/Intl/DateTimeFormat.h
index 4a36843663..d72917c346 100644
--- a/Libraries/LibJS/Runtime/Intl/DateTimeFormat.h
+++ b/Libraries/LibJS/Runtime/Intl/DateTimeFormat.h
@@ -10,6 +10,7 @@
 #include <AK/String.h>
 #include <AK/StringView.h>
 #include <AK/Types.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 #include <AK/Vector.h>
 #include <LibJS/Runtime/Completion.h>
@@ -29,32 +30,32 @@ class DateTimeFormat final : public IntlObject {
 public:
     virtual ~DateTimeFormat() override = default;
 
-    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<Utf16View> relevant_extension_keys() const override;
     virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
 
-    String const& locale() const { return m_locale; }
-    void set_locale(String locale) { m_locale = move(locale); }
+    Utf16String const& locale() const { return m_locale; }
+    void set_locale(Utf16String locale) { m_locale = move(locale); }
 
-    String const& icu_locale() const { return m_icu_locale; }
-    void set_icu_locale(String icu_locale) { m_icu_locale = move(icu_locale); }
+    Utf16String const& icu_locale() const { return m_icu_locale; }
+    void set_icu_locale(Utf16String icu_locale) { m_icu_locale = move(icu_locale); }
 
-    String const& calendar() const { return m_calendar; }
-    void set_calendar(String calendar) { m_calendar = move(calendar); }
+    Utf16String const& calendar() const { return m_calendar; }
+    void set_calendar(Utf16String calendar) { m_calendar = move(calendar); }
 
-    String const& numbering_system() const { return m_numbering_system; }
-    void set_numbering_system(String numbering_system) { m_numbering_system = move(numbering_system); }
+    Utf16String const& numbering_system() const { return m_numbering_system; }
+    void set_numbering_system(Utf16String numbering_system) { m_numbering_system = move(numbering_system); }
 
-    String const& time_zone() const { return m_time_zone; }
-    void set_time_zone(String time_zone) { m_time_zone = move(time_zone); }
+    Utf16String const& time_zone() const { return m_time_zone; }
+    void set_time_zone(Utf16String time_zone) { m_time_zone = move(time_zone); }
 
     bool has_date_style() const { return m_date_style.has_value(); }
     Optional<Unicode::DateTimeStyle> const& date_style() const { return m_date_style; }
-    StringView date_style_string() const { return Unicode::date_time_style_to_string(*m_date_style); }
+    Utf16String date_style_string() const { return Unicode::date_time_style_to_string(*m_date_style); }
     void set_date_style(Utf16View style) { m_date_style = Unicode::date_time_style_from_string(style); }
 
     bool has_time_style() const { return m_time_style.has_value(); }
     Optional<Unicode::DateTimeStyle> const& time_style() const { return m_time_style; }
-    StringView time_style_string() const { return Unicode::date_time_style_to_string(*m_time_style); }
+    Utf16String time_style_string() const { return Unicode::date_time_style_to_string(*m_time_style); }
     void set_time_style(Utf16View style) { m_time_style = Unicode::date_time_style_from_string(style); }
 
     Unicode::CalendarPattern& date_time_format() { return m_date_time_format; }
@@ -84,17 +85,17 @@ public:
     Optional<Unicode::DateTimeFormat const&> temporal_instant_formatter();
     void set_temporal_instant_format(Optional<Unicode::CalendarPattern> temporal_instant_format) { m_temporal_instant_format = move(temporal_instant_format); }
 
-    void set_temporal_time_zone(String temporal_time_zone) { m_temporal_time_zone = move(temporal_time_zone); }
+    void set_temporal_time_zone(Utf16String temporal_time_zone) { m_temporal_time_zone = move(temporal_time_zone); }
 
 private:
     explicit DateTimeFormat(Object& prototype);
 
     virtual void visit_edges(Visitor&) override;
 
-    String m_locale;                                                       // [[Locale]]
-    String m_calendar;                                                     // [[Calendar]]
-    String m_numbering_system;                                             // [[NumberingSystem]]
-    String m_time_zone;                                                    // [[TimeZone]]
+    Utf16String m_locale;                                                  // [[Locale]]
+    Utf16String m_calendar;                                                // [[Calendar]]
+    Utf16String m_numbering_system;                                        // [[NumberingSystem]]
+    Utf16String m_time_zone;                                               // [[TimeZone]]
     Optional<Unicode::DateTimeStyle> m_date_style;                         // [[DateStyle]]
     Optional<Unicode::DateTimeStyle> m_time_style;                         // [[TimeStyle]]
     Unicode::CalendarPattern m_date_time_format;                           // [[DateTimeFormat]]
@@ -107,7 +108,7 @@ private:
     GC::Ptr<NativeFunction> m_bound_format;                                // [[BoundFormat]]
 
     // Non-standard. Stores the ICU date-time formatters for the Intl object's formatting options.
-    String m_icu_locale;
+    Utf16String m_icu_locale;
     OwnPtr<Unicode::DateTimeFormat> m_formatter;
     OwnPtr<Unicode::DateTimeFormat> m_temporal_plain_date_formatter;
     OwnPtr<Unicode::DateTimeFormat> m_temporal_plain_year_month_formatter;
@@ -115,7 +116,7 @@ private:
     OwnPtr<Unicode::DateTimeFormat> m_temporal_plain_time_formatter;
     OwnPtr<Unicode::DateTimeFormat> m_temporal_plain_date_time_formatter;
     OwnPtr<Unicode::DateTimeFormat> m_temporal_instant_formatter;
-    String m_temporal_time_zone;
+    Utf16String m_temporal_time_zone;
 };
 
 using FormattableDateTime = Variant<
diff --git a/Libraries/LibJS/Runtime/Intl/DateTimeFormatConstructor.cpp b/Libraries/LibJS/Runtime/Intl/DateTimeFormatConstructor.cpp
index 3bfef10276..b0143ef781 100644
--- a/Libraries/LibJS/Runtime/Intl/DateTimeFormatConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Intl/DateTimeFormatConstructor.cpp
@@ -85,7 +85,7 @@ JS_DEFINE_NATIVE_FUNCTION(DateTimeFormatConstructor::supported_locales_of)
 // 11.1.2 CreateDateTimeFormat ( newTarget, locales, options, required, defaults ), https://tc39.es/ecma402/#sec-createdatetimeformat
 // 15.4.1 CreateDateTimeFormat ( newTarget, locales, options, required, defaults [ , toLocaleStringTimeZone ] ), https://tc39.es/proposal-temporal/#sec-createdatetimeformat
 // 3.1.1 CreateDateTimeFormat ( newTarget, locales, options, required, defaults ), https://tc39.es/proposal-intl-era-monthcode/#sec-ecma402-intl-datetimeformat-constructor
-ThrowCompletionOr<GC::Ref<DateTimeFormat>> create_date_time_format(VM& vm, FunctionObject& new_target, Value locales_value, Value options_value, OptionRequired required, OptionDefaults defaults, Optional<String> const& to_locale_string_time_zone)
+ThrowCompletionOr<GC::Ref<DateTimeFormat>> create_date_time_format(VM& vm, FunctionObject& new_target, Value locales_value, Value options_value, OptionRequired required, OptionDefaults defaults, Optional<Utf16View> const& to_locale_string_time_zone)
 {
     // 1. Let dateTimeFormat be ? OrdinaryCreateFromConstructor(newTarget, "%Intl.DateTimeFormat.prototype%", « [[InitializedDateTimeFormat]], [[Locale]], [[Calendar]], [[NumberingSystem]], [[TimeZone]], [[HourCycle]], [[DateStyle]], [[TimeStyle]], [[DateTimeFormat]], [[BoundFormat]] »).
     auto date_time_format = TRY(ordinary_create_from_constructor<DateTimeFormat>(vm, new_target, &Intrinsics::intl_date_time_format_prototype));
@@ -115,27 +115,27 @@ ThrowCompletionOr<GC::Ref<DateTimeFormat>> create_date_time_format(VM& vm, Funct
     date_time_format->set_locale(move(result.locale));
 
     // 8. Let resolvedCalendar be r.[[ca]].
-    if (auto* resolved_calendar = result.ca.get_pointer<String>()) {
+    if (auto* resolved_calendar = result.ca.get_pointer<Utf16String>()) {
         // 9. If resolvedCalendar is "islamic", then
         // NB: We also make "islamic-rgsa" fall back to "islamic-tbla", as test262 relies on this behavior. This falls
         //     within implementation-defined behavior. See:
         //     https://github.com/tc39/ecma402/pull/1044#discussion_r2926804980
-        if (resolved_calendar->is_one_of("islamic"sv, "islamic-rgsa"sv)) {
+        if (resolved_calendar->utf16_view().is_one_of("islamic"sv, "islamic-rgsa"sv)) {
             // a. Set resolvedCalendar to "islamic-tbla".
-            *resolved_calendar = "islamic-tbla"_string;
+            date_time_format->set_calendar("islamic-tbla"_utf16);
 
             // b. If the ECMAScript implementation has a mechanism for reporting diagnostic warning messages, a warning
             //    should be issued.
+        } else {
+            // 10. Set dateTimeFormat.[[Calendar]] to resolvedCalendar.
+            date_time_format->set_calendar(move(*resolved_calendar));
         }
-
-        // 10. Set dateTimeFormat.[[Calendar]] to resolvedCalendar.
-        date_time_format->set_calendar(move(*resolved_calendar));
     }
 
     date_time_format->set_icu_locale(move(result.icu_locale));
 
     // 11. Set dateTimeFormat.[[NumberingSystem]] to r.[[nu]].
-    if (auto* resolved_numbering_system = result.nu.get_pointer<String>())
+    if (auto* resolved_numbering_system = result.nu.get_pointer<Utf16String>())
         date_time_format->set_numbering_system(move(*resolved_numbering_system));
 
     // 12. Let resolvedLocaleData be r.[[LocaleData]].
@@ -157,12 +157,12 @@ ThrowCompletionOr<GC::Ref<DateTimeFormat>> create_date_time_format(VM& vm, Funct
         VERIFY(hour12.is_undefined());
 
         // b. Let hc be r.[[hc]].
-        if (auto* resolved_hour_cycle = result.hc.get_pointer<String>())
-            hour_cycle_value = Unicode::hour_cycle_from_string(*resolved_hour_cycle);
+        if (auto* resolved_hour_cycle = result.hc.get_pointer<Utf16String>())
+            hour_cycle_value = Unicode::hour_cycle_from_string(resolved_hour_cycle->utf16_view());
 
         // c. If hc is null, set hc to resolvedLocaleData.[[hourCycle]].
         if (!hour_cycle_value.has_value())
-            hour_cycle_value = Unicode::default_hour_cycle(date_time_format->locale());
+            hour_cycle_value = Unicode::default_hour_cycle(date_time_format->icu_locale().utf16_view());
     }
 
     // 16. Set dateTimeFormat.[[HourCycle]] to hc.
@@ -170,22 +170,21 @@ ThrowCompletionOr<GC::Ref<DateTimeFormat>> create_date_time_format(VM& vm, Funct
 
     // 17. Let timeZone be ? Get(options, "timeZone").
     auto time_zone_value = TRY(options->get(vm.names.timeZone));
-    String time_zone;
-    Utf16String time_zone_string;
+    Utf16String icu_time_zone;
+    Utf16String time_zone;
 
     // 18. If timeZone is undefined, then
     if (time_zone_value.is_undefined()) {
         // a. If toLocaleStringTimeZone is present, then
         if (to_locale_string_time_zone.has_value()) {
             // i. Set timeZone to toLocaleStringTimeZone.
-            time_zone = *to_locale_string_time_zone;
-            time_zone_string = Utf16String::from_utf8(time_zone);
+            time_zone = Utf16String::from_utf16(*to_locale_string_time_zone);
         }
         // b. Else,
         else {
             // i. Set timeZone to SystemTimeZoneIdentifier().
             time_zone = system_time_zone_identifier();
-            time_zone_string = Utf16String::from_utf8(time_zone);
+            icu_time_zone = time_zone;
         }
     }
     // 19. Else,
@@ -195,10 +194,10 @@ ThrowCompletionOr<GC::Ref<DateTimeFormat>> create_date_time_format(VM& vm, Funct
             return vm.throw_completion<TypeError>(ErrorType::IntlInvalidDateTimeFormatOption, vm.names.timeZone, "a toLocaleString time zone"sv);
 
         // b. Set timeZone to ? ToString(timeZone).
-        time_zone_string = TRY(time_zone_value.to_utf16_string(vm));
+        time_zone = TRY(time_zone_value.to_utf16_string(vm));
     }
 
-    auto time_zone_view = time_zone_string.utf16_view();
+    auto time_zone_view = time_zone.utf16_view();
 
     // 20. If IsTimeZoneOffsetString(timeZone) is true, then
     auto parse_result = Temporal::parse_utc_offset(time_zone_view, Temporal::SubMinutePrecision::No);
@@ -218,33 +217,31 @@ ThrowCompletionOr<GC::Ref<DateTimeFormat>> create_date_time_format(VM& vm, Funct
 
         // e. Set timeZone to FormatOffsetTimeZoneIdentifier(offsetMinutes).
         time_zone = format_offset_time_zone_identifier(offset_minutes);
+        icu_time_zone = time_zone;
     }
     // 21. Else,
     else {
         // a. Let timeZoneIdentifierRecord be GetAvailableNamedTimeZoneIdentifier(timeZone).
-        if (!time_zone_view.is_ascii())
-            return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, time_zone_view, vm.names.timeZone);
-
-        time_zone = MUST(time_zone_view.to_utf8());
-        auto time_zone_identifier_record = get_available_named_time_zone_identifier(time_zone);
+        auto time_zone_identifier_record = get_available_named_time_zone_identifier(time_zone_view);
 
         // b. If timeZoneIdentifierRecord is EMPTY, throw a RangeError exception.
         if (!time_zone_identifier_record.has_value())
-            return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, time_zone, vm.names.timeZone);
+            return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, time_zone_view, vm.names.timeZone);
 
         // c. Set timeZone to timeZoneIdentifierRecord.[[Identifier]].
         time_zone = time_zone_identifier_record->identifier;
+        icu_time_zone = time_zone;
     }
 
     // 22. Set dateTimeFormat.[[TimeZone]] to timeZone.
-    date_time_format->set_time_zone(time_zone);
+    date_time_format->set_time_zone(move(time_zone));
 
     // NOTE: ICU requires time zone offset strings to be of the form "GMT+00:00"
     if (is_time_zone_offset_string)
-        time_zone = MUST(String::formatted("GMT{}", time_zone));
+        icu_time_zone = Utf16String::formatted("GMT{}", icu_time_zone);
 
     // AD-HOC: We must store the massaged time zone for creating ICU formatters for Temporal objects.
-    date_time_format->set_temporal_time_zone(time_zone);
+    date_time_format->set_temporal_time_zone(icu_time_zone);
 
     // 23. Let formatOptions be a new Record.
     Unicode::CalendarPattern format_options {};
@@ -297,7 +294,7 @@ ThrowCompletionOr<GC::Ref<DateTimeFormat>> create_date_time_format(VM& vm, Funct
     }));
 
     // 27. Let formatMatcher be ? GetOption(options, "formatMatcher", string, « "basic", "best fit" », "best fit").
-    [[maybe_unused]] auto format_matcher = TRY(get_option(vm, *options, vm.names.formatMatcher, OptionType::String, AK::Array { "basic"sv, "best fit"sv }, "best fit"sv));
+    [[maybe_unused]] auto format_matcher = TRY(get_option(vm, *options, vm.names.formatMatcher, OptionType::String, AK::Array { "basic"sv, "best fit"sv }, u"best fit"sv));
 
     // 28. Let dateStyle be ? GetOption(options, "dateStyle", string, « "full", "long", "medium", "short" », undefined).
     auto date_style = TRY(get_option(vm, *options, vm.names.dateStyle, OptionType::String, AK::Array { "full"sv, "long"sv, "medium"sv, "short"sv }, Empty {}));
@@ -340,8 +337,8 @@ ThrowCompletionOr<GC::Ref<DateTimeFormat>> create_date_time_format(VM& vm, Funct
         // d. Let styles be resolvedLocaleData.[[styles]].[[<resolvedCalendar>]].
         // e. Let bestFormat be DateTimeStyleFormat(dateStyle, timeStyle, styles).
         formatter = Unicode::DateTimeFormat::create_for_date_and_time_style(
-            date_time_format->icu_locale(),
-            time_zone,
+            date_time_format->icu_locale().utf16_view().bytes(),
+            icu_time_zone.utf16_view().bytes(),
             format_options.hour_cycle,
             format_options.hour12,
             date_time_format->date_style(),
@@ -428,8 +425,8 @@ ThrowCompletionOr<GC::Ref<DateTimeFormat>> create_date_time_format(VM& vm, Funct
         }
 
         formatter = Unicode::DateTimeFormat::create_for_pattern_options(
-            date_time_format->icu_locale(),
-            time_zone,
+            date_time_format->icu_locale().utf16_view().bytes(),
+            icu_time_zone.utf16_view().bytes(),
             best_format);
     }
 
@@ -444,7 +441,7 @@ ThrowCompletionOr<GC::Ref<DateTimeFormat>> create_date_time_format(VM& vm, Funct
 }
 
 // 11.1.3 FormatOffsetTimeZoneIdentifier ( offsetMinutes ), https://tc39.es/ecma402/#sec-formatoffsettimezoneidentifier
-String format_offset_time_zone_identifier(double offset_minutes)
+Utf16String format_offset_time_zone_identifier(double offset_minutes)
 {
     // 1. If offsetMinutes ≥ 0, let sign be the code unit 0x002B (PLUS SIGN); otherwise, let sign be the code unit 0x002D (HYPHEN-MINUS).
     auto sign = offset_minutes >= 0.0 ? '+' : '-';
@@ -459,7 +456,7 @@ String format_offset_time_zone_identifier(double offset_minutes)
     auto minutes = static_cast<i64>(modulo(absolute_minutes, 60.0));
 
     // 5. Return the string-concatenation of sign, ToZeroPaddedDecimalString(hours, 2), the code unit 0x003A (COLON), and ToZeroPaddedDecimalString(minutes, 2).
-    return MUST(String::formatted("{}{:02}:{:02}", sign, hours, minutes));
+    return Utf16String::formatted("{}{:02}:{:02}", sign, hours, minutes);
 }
 
 }
diff --git a/Libraries/LibJS/Runtime/Intl/DateTimeFormatConstructor.h b/Libraries/LibJS/Runtime/Intl/DateTimeFormatConstructor.h
index 1890f8926b..76bd97c798 100644
--- a/Libraries/LibJS/Runtime/Intl/DateTimeFormatConstructor.h
+++ b/Libraries/LibJS/Runtime/Intl/DateTimeFormatConstructor.h
@@ -51,7 +51,7 @@ enum class OptionInherit {
     Relevant,
 };
 
-ThrowCompletionOr<GC::Ref<DateTimeFormat>> create_date_time_format(VM&, FunctionObject& new_target, Value locales_value, Value options_value, OptionRequired, OptionDefaults, Optional<String> const& to_locale_string_time_zone = {});
-String format_offset_time_zone_identifier(double offset_minutes);
+ThrowCompletionOr<GC::Ref<DateTimeFormat>> create_date_time_format(VM&, FunctionObject& new_target, Value locales_value, Value options_value, OptionRequired, OptionDefaults, Optional<Utf16View> const& to_locale_string_time_zone = {});
+Utf16String format_offset_time_zone_identifier(double offset_minutes);
 
 }
diff --git a/Libraries/LibJS/Runtime/Intl/DateTimeFormatFunction.cpp b/Libraries/LibJS/Runtime/Intl/DateTimeFormatFunction.cpp
index 2b6daca036..e4fe5e514b 100644
--- a/Libraries/LibJS/Runtime/Intl/DateTimeFormatFunction.cpp
+++ b/Libraries/LibJS/Runtime/Intl/DateTimeFormatFunction.cpp
@@ -35,7 +35,7 @@ void DateTimeFormatFunction::initialize(Realm& realm)
 
     Base::initialize(realm);
     define_direct_property(vm.names.length, Value(1), Attribute::Configurable);
-    define_direct_property(vm.names.name, PrimitiveString::create(vm, String {}), Attribute::Configurable);
+    define_direct_property(vm.names.name, PrimitiveString::create(vm, Utf16String {}), Attribute::Configurable);
 }
 
 ThrowCompletionOr<Value> DateTimeFormatFunction::call()
diff --git a/Libraries/LibJS/Runtime/Intl/DateTimeFormatPrototype.cpp b/Libraries/LibJS/Runtime/Intl/DateTimeFormatPrototype.cpp
index 50eeb2b1d5..402e42dc90 100644
--- a/Libraries/LibJS/Runtime/Intl/DateTimeFormatPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Intl/DateTimeFormatPrototype.cpp
@@ -29,7 +29,7 @@ void DateTimeFormatPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 11.3.7 Intl.DateTimeFormat.prototype [ %Symbol.toStringTag% ], https://tc39.es/ecma402/#sec-intl.datetimeformat.prototype-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.DateTimeFormat"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.DateTimeFormat"_utf16_fly_string), Attribute::Configurable);
 
     define_native_accessor(realm, vm.names.format, format, nullptr, Attribute::Configurable);
 
@@ -104,7 +104,7 @@ JS_DEFINE_NATIVE_FUNCTION(DateTimeFormatPrototype::resolved_options)
                 MUST(options->create_data_property_or_throw(property, Value(*option)));
             } else {
                 auto name = Unicode::calendar_pattern_style_to_string(*option);
-                MUST(options->create_data_property_or_throw(property, PrimitiveString::create(vm, name)));
+                MUST(options->create_data_property_or_throw(property, PrimitiveString::create(vm, move(name))));
             }
 
             return {};
diff --git a/Libraries/LibJS/Runtime/Intl/DisplayNames.cpp b/Libraries/LibJS/Runtime/Intl/DisplayNames.cpp
index 2b00413345..6e81267e34 100644
--- a/Libraries/LibJS/Runtime/Intl/DisplayNames.cpp
+++ b/Libraries/LibJS/Runtime/Intl/DisplayNames.cpp
@@ -19,7 +19,7 @@ DisplayNames::DisplayNames(Object& prototype)
 }
 
 // 12.2.3 Internal slots, https://tc39.es/ecma402/#sec-Intl.DisplayNames-internal-slots
-ReadonlySpan<StringView> DisplayNames::relevant_extension_keys() const
+ReadonlySpan<Utf16View> DisplayNames::relevant_extension_keys() const
 {
     // The value of the [[RelevantExtensionKeys]] internal slot is « ».
     return {};
@@ -50,21 +50,21 @@ void DisplayNames::set_type(Utf16View type)
         VERIFY_NOT_REACHED();
 }
 
-StringView DisplayNames::type_string() const
+Utf16String DisplayNames::type_string() const
 {
     switch (m_type) {
     case Type::Language:
-        return "language"sv;
+        return "language"_utf16;
     case Type::Region:
-        return "region"sv;
+        return "region"_utf16;
     case Type::Script:
-        return "script"sv;
+        return "script"_utf16;
     case Type::Currency:
-        return "currency"sv;
+        return "currency"_utf16;
     case Type::Calendar:
-        return "calendar"sv;
+        return "calendar"_utf16;
     case Type::DateTimeField:
-        return "dateTimeField"sv;
+        return "dateTimeField"_utf16;
     default:
         VERIFY_NOT_REACHED();
     }
@@ -80,13 +80,13 @@ void DisplayNames::set_fallback(Utf16View fallback)
         VERIFY_NOT_REACHED();
 }
 
-StringView DisplayNames::fallback_string() const
+Utf16String DisplayNames::fallback_string() const
 {
     switch (m_fallback) {
     case Fallback::None:
-        return "none"sv;
+        return "none"_utf16;
     case Fallback::Code:
-        return "code"sv;
+        return "code"_utf16;
     default:
         VERIFY_NOT_REACHED();
     }
@@ -97,22 +97,17 @@ ThrowCompletionOr<Value> canonical_code_for_display_names(VM& vm, DisplayNames::
 {
     // 1. If type is "language", then
     if (type == DisplayNames::Type::Language) {
-        if (!code.is_ascii())
-            return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, code, "language"sv);
-
-        auto code_string = MUST(code.to_utf8());
-
         // a. If code does not match the unicode_language_id production, throw a RangeError exception.
-        if (!Unicode::parse_unicode_language_id(code_string).has_value())
+        if (!Unicode::parse_unicode_language_id(code).has_value())
             return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, code, "language"sv);
 
         // b. If IsWellFormedLanguageTag(code) is false, throw a RangeError exception.
-        if (!is_well_formed_language_tag(code_string))
+        if (!is_well_formed_language_tag(code))
             return vm.throw_completion<RangeError>(ErrorType::IntlInvalidLanguageTag, code);
 
         // c. Return ! CanonicalizeUnicodeLocaleId(code).
-        auto canonicalized_tag = canonicalize_unicode_locale_id(code_string);
-        return PrimitiveString::create(vm, move(canonicalized_tag));
+        auto canonicalized_tag = canonicalize_unicode_locale_id(code);
+        return PrimitiveString::create(vm, canonicalized_tag);
     }
 
     // 2. If type is "region", then
diff --git a/Libraries/LibJS/Runtime/Intl/DisplayNames.h b/Libraries/LibJS/Runtime/Intl/DisplayNames.h
index 712f8b8458..495245b98f 100644
--- a/Libraries/LibJS/Runtime/Intl/DisplayNames.h
+++ b/Libraries/LibJS/Runtime/Intl/DisplayNames.h
@@ -9,6 +9,7 @@
 #include <AK/Optional.h>
 #include <AK/String.h>
 #include <AK/StringView.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 #include <LibJS/Runtime/Intl/IntlObject.h>
 #include <LibUnicode/DisplayNames.h>
@@ -39,37 +40,43 @@ class DisplayNames final : public IntlObject {
 public:
     virtual ~DisplayNames() override = default;
 
-    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<Utf16View> relevant_extension_keys() const override;
     virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
 
-    String const& locale() const { return m_locale; }
-    void set_locale(String locale) { m_locale = move(locale); }
+    Utf16String const& locale() const { return m_locale; }
+    void set_locale(Utf16String locale) { m_locale = move(locale); }
+
+    Utf16String const& icu_locale() const { return m_icu_locale; }
+    void set_icu_locale(Utf16String icu_locale) { m_icu_locale = move(icu_locale); }
 
     Unicode::Style style() const { return m_style; }
     void set_style(Utf16View style) { m_style = Unicode::style_from_string(style); }
-    StringView style_string() const { return Unicode::style_to_string(m_style); }
+    Utf16String style_string() const { return Unicode::style_to_string(m_style); }
 
     Type type() const { return m_type; }
     void set_type(Utf16View type);
-    StringView type_string() const;
+    Utf16String type_string() const;
 
     Fallback fallback() const { return m_fallback; }
     void set_fallback(Utf16View fallback);
-    StringView fallback_string() const;
+    Utf16String fallback_string() const;
 
     bool has_language_display() const { return m_language_display.has_value(); }
     Unicode::LanguageDisplay language_display() const { return *m_language_display; }
     void set_language_display(Utf16View language_display) { m_language_display = Unicode::language_display_from_string(language_display); }
-    StringView language_display_string() const { return Unicode::language_display_to_string(*m_language_display); }
+    Utf16String language_display_string() const { return Unicode::language_display_to_string(*m_language_display); }
 
 private:
     explicit DisplayNames(Object& prototype);
 
-    String m_locale;                                       // [[Locale]]
+    Utf16String m_locale;                                  // [[Locale]]
     Unicode::Style m_style { Unicode::Style::Long };       // [[Style]]
     Type m_type { Type::Invalid };                         // [[Type]]
     Fallback m_fallback { Fallback::Invalid };             // [[Fallback]]
     Optional<Unicode::LanguageDisplay> m_language_display; // [[LanguageDisplay]]
+
+    // Non-standard. Stores the ICU locale for display-name lookups.
+    Utf16String m_icu_locale;
 };
 
 ThrowCompletionOr<Value> canonical_code_for_display_names(VM&, DisplayNames::Type, Utf16View code);
diff --git a/Libraries/LibJS/Runtime/Intl/DisplayNamesConstructor.cpp b/Libraries/LibJS/Runtime/Intl/DisplayNamesConstructor.cpp
index 75bf0d9d06..003b0baf7f 100644
--- a/Libraries/LibJS/Runtime/Intl/DisplayNamesConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Intl/DisplayNamesConstructor.cpp
@@ -61,7 +61,7 @@ ThrowCompletionOr<GC::Ref<Object>> DisplayNamesConstructor::construct(FunctionOb
     auto [options, result, _] = TRY(resolve_options(vm, display_names, locales_value, options_value, SpecialBehaviors::RequireOptions));
 
     // 6. Let style be ? GetOption(options, "style", string, « "narrow", "short", "long" », "long").
-    auto style = TRY(get_option(vm, *options, vm.names.style, OptionType::String, { "narrow"sv, "short"sv, "long"sv }, "long"sv));
+    auto style = TRY(get_option(vm, *options, vm.names.style, OptionType::String, { "narrow"sv, "short"sv, "long"sv }, u"long"sv));
 
     // 7. Set displayNames.[[Style]] to style.
     display_names->set_style(style.as_string().utf16_string_view());
@@ -77,20 +77,21 @@ ThrowCompletionOr<GC::Ref<Object>> DisplayNamesConstructor::construct(FunctionOb
     display_names->set_type(type.as_string().utf16_string_view());
 
     // 11. Let fallback be ? GetOption(options, "fallback", string, « "code", "none" », "code").
-    auto fallback = TRY(get_option(vm, *options, vm.names.fallback, OptionType::String, { "code"sv, "none"sv }, "code"sv));
+    auto fallback = TRY(get_option(vm, *options, vm.names.fallback, OptionType::String, { "code"sv, "none"sv }, u"code"sv));
 
     // 12. Set displayNames.[[Fallback]] to fallback.
     display_names->set_fallback(fallback.as_string().utf16_string_view());
 
     // 13. Set displayNames.[[Locale]] to r.[[Locale]].
     display_names->set_locale(move(result.locale));
+    display_names->set_icu_locale(move(result.icu_locale));
 
     // 14. Let resolvedLocaleData be r.[[LocaleData]].
     // 15. Let types be resolvedLocaleData.[[types]].
     // 16. Assert: types is a Record (see 12.2.3).
 
     // 17. Let languageDisplay be ? GetOption(options, "languageDisplay", string, « "dialect", "standard" », "dialect").
-    auto language_display = TRY(get_option(vm, *options, vm.names.languageDisplay, OptionType::String, { "dialect"sv, "standard"sv }, "dialect"sv));
+    auto language_display = TRY(get_option(vm, *options, vm.names.languageDisplay, OptionType::String, { "dialect"sv, "standard"sv }, u"dialect"sv));
 
     // 18. Let typeFields be types.[[<type>]].
     // 19. Assert: typeFields is a Record (see 12.2.3).
diff --git a/Libraries/LibJS/Runtime/Intl/DisplayNamesPrototype.cpp b/Libraries/LibJS/Runtime/Intl/DisplayNamesPrototype.cpp
index b827db8c0e..ac56f78bdb 100644
--- a/Libraries/LibJS/Runtime/Intl/DisplayNamesPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Intl/DisplayNamesPrototype.cpp
@@ -28,7 +28,7 @@ void DisplayNamesPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 12.3.4 Intl.DisplayNames.prototype [ %Symbol.toStringTag% ], https://tc39.es/ecma402/#sec-intl.displaynames.prototype-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.DisplayNames"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.DisplayNames"_utf16_fly_string), Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(realm, vm.names.resolvedOptions, resolved_options, 0, attr);
@@ -78,7 +78,7 @@ JS_DEFINE_NATIVE_FUNCTION(DisplayNamesPrototype::of)
 
     // 4. Let code be ? CanonicalCodeForDisplayNames(displayNames.[[Type]], code).
     code = TRY(canonical_code_for_display_names(vm, display_names->type(), code.as_string().utf16_string_view()));
-    auto code_string = MUST(code.as_string().utf16_string_view().to_utf8());
+    auto code_view = code.as_string().utf16_string_view();
 
     // 5. Let fields be displayNames.[[Fields]].
     // 6. If fields has a field [[<code>]], return fields.[[<code>]].
@@ -86,22 +86,22 @@ JS_DEFINE_NATIVE_FUNCTION(DisplayNamesPrototype::of)
 
     switch (display_names->type()) {
     case DisplayNames::Type::Language:
-        result = Unicode::language_display_name(display_names->locale(), code_string, display_names->language_display());
+        result = Unicode::language_display_name(display_names->icu_locale().utf16_view().bytes(), code_view, display_names->language_display());
         break;
     case DisplayNames::Type::Region:
-        result = Unicode::region_display_name(display_names->locale(), code_string);
+        result = Unicode::region_display_name(display_names->icu_locale().utf16_view().bytes(), code_view);
         break;
     case DisplayNames::Type::Script:
-        result = Unicode::script_display_name(display_names->locale(), code_string);
+        result = Unicode::script_display_name(display_names->icu_locale().utf16_view().bytes(), code_view);
         break;
     case DisplayNames::Type::Currency:
-        result = Unicode::currency_display_name(display_names->locale(), code_string, display_names->style());
+        result = Unicode::currency_display_name(display_names->icu_locale().utf16_view().bytes(), code_view, display_names->style());
         break;
     case DisplayNames::Type::Calendar:
-        result = Unicode::calendar_display_name(display_names->locale(), code_string);
+        result = Unicode::calendar_display_name(display_names->icu_locale().utf16_view().bytes(), code_view);
         break;
     case DisplayNames::Type::DateTimeField:
-        result = Unicode::date_time_field_display_name(display_names->locale(), code_string, display_names->style());
+        result = Unicode::date_time_field_display_name(display_names->icu_locale().utf16_view().bytes(), code_view, display_names->style());
         break;
     default:
         VERIFY_NOT_REACHED();
diff --git a/Libraries/LibJS/Runtime/Intl/DurationFormat.cpp b/Libraries/LibJS/Runtime/Intl/DurationFormat.cpp
index b2dc11818e..a0a174df77 100644
--- a/Libraries/LibJS/Runtime/Intl/DurationFormat.cpp
+++ b/Libraries/LibJS/Runtime/Intl/DurationFormat.cpp
@@ -29,10 +29,10 @@ DurationFormat::DurationFormat(Object& prototype)
 }
 
 // 13.2.3 Internal slots, https://tc39.es/ecma402/#sec-Intl.DurationFormat-internal-slots
-ReadonlySpan<StringView> DurationFormat::relevant_extension_keys() const
+ReadonlySpan<Utf16View> DurationFormat::relevant_extension_keys() const
 {
     // The value of the [[RelevantExtensionKeys]] internal slot is « "nu" ».
-    static constexpr AK::Array keys { "nu"sv };
+    static constexpr AK::Array<Utf16View, 1> keys { "nu"sv };
     return keys;
 }
 
@@ -63,17 +63,17 @@ DurationFormat::Style DurationFormat::style_from_string(Utf16View style)
     VERIFY_NOT_REACHED();
 }
 
-StringView DurationFormat::style_to_string(Style style)
+Utf16String DurationFormat::style_to_string(Style style)
 {
     switch (style) {
     case Style::Long:
-        return "long"sv;
+        return "long"_utf16;
     case Style::Short:
-        return "short"sv;
+        return "short"_utf16;
     case Style::Narrow:
-        return "narrow"sv;
+        return "narrow"_utf16;
     case Style::Digital:
-        return "digital"sv;
+        return "digital"_utf16;
     default:
         VERIFY_NOT_REACHED();
     }
@@ -105,32 +105,32 @@ DurationFormat::ValueStyle DurationFormat::value_style_from_string(Utf16View val
     VERIFY_NOT_REACHED();
 }
 
-StringView DurationFormat::value_style_to_string(ValueStyle value_style)
+Utf16String DurationFormat::value_style_to_string(ValueStyle value_style)
 {
     switch (value_style) {
     case ValueStyle::Long:
-        return "long"sv;
+        return "long"_utf16;
     case ValueStyle::Short:
-        return "short"sv;
+        return "short"_utf16;
     case ValueStyle::Narrow:
-        return "narrow"sv;
+        return "narrow"_utf16;
     case ValueStyle::Numeric:
-        return "numeric"sv;
+        return "numeric"_utf16;
     case ValueStyle::TwoDigit:
-        return "2-digit"sv;
+        return "2-digit"_utf16;
     case ValueStyle::Fractional:
-        return "fractional"sv;
+        return "fractional"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
 
-StringView DurationFormat::display_to_string(Display display)
+Utf16String DurationFormat::display_to_string(Display display)
 {
     switch (display) {
     case Display::Auto:
-        return "auto"sv;
+        return "auto"_utf16;
     case Display::Always:
-        return "always"sv;
+        return "always"_utf16;
     default:
         VERIFY_NOT_REACHED();
     }
@@ -238,7 +238,7 @@ ThrowCompletionOr<DurationFormat::DurationUnitOptions> get_duration_unit_options
     DurationFormat::ValueStyle style;
 
     // 2. Let displayDefault be "always".
-    auto display_default = "always"sv;
+    Utf16View display_default = u"always"sv;
 
     // 3. If style is undefined, then
     if (style_value.is_undefined()) {
@@ -249,7 +249,7 @@ ThrowCompletionOr<DurationFormat::DurationUnitOptions> get_duration_unit_options
 
             // ii. If unit is not one of "hours", "minutes", or "seconds", set displayDefault to "auto".
             if (!first_is_one_of(unit, DurationFormat::Unit::Hours, DurationFormat::Unit::Minutes, DurationFormat::Unit::Seconds))
-                display_default = "auto"sv;
+                display_default = u"auto"sv;
         }
         // b. Else if prevStyle is one of "fractional", "numeric" or "2-digit", then
         else if (first_is_one_of(previous_style, DurationFormat::ValueStyle::Fractional, DurationFormat::ValueStyle::Numeric, DurationFormat::ValueStyle::TwoDigit)) {
@@ -258,7 +258,7 @@ ThrowCompletionOr<DurationFormat::DurationUnitOptions> get_duration_unit_options
 
             // ii. If unit is not "minutes" or "seconds", set displayDefault to "auto".
             if (!first_is_one_of(unit, DurationFormat::Unit::Minutes, DurationFormat::Unit::Seconds))
-                display_default = "auto"sv;
+                display_default = u"auto"sv;
         }
         // c. Else,
         else {
@@ -266,7 +266,7 @@ ThrowCompletionOr<DurationFormat::DurationUnitOptions> get_duration_unit_options
             style = static_cast<DurationFormat::ValueStyle>(base_style);
 
             // ii. Set displayDefault to "auto".
-            display_default = "auto"sv;
+            display_default = u"auto"sv;
         }
     } else {
         style = DurationFormat::value_style_from_string(style_value.as_string().utf16_string_view());
@@ -278,7 +278,7 @@ ThrowCompletionOr<DurationFormat::DurationUnitOptions> get_duration_unit_options
         style = DurationFormat::ValueStyle::Fractional;
 
         // b. Set displayDefault to "auto".
-        display_default = "auto"sv;
+        display_default = u"auto"sv;
     }
 
     // 5. Let displayField be the string-concatenation of unit and "Display".
@@ -395,7 +395,7 @@ Vector<DurationFormatPart> format_numeric_hours(VM& vm, DurationFormat const& du
     // 8. If signDisplayed is false, then
     if (!sign_displayed) {
         // a. Perform ! CreateDataPropertyOrThrow(nfOpts, "signDisplay", "never").
-        MUST(number_format_options->create_data_property_or_throw(vm.names.signDisplay, PrimitiveString::create(vm, "never"sv)));
+        MUST(number_format_options->create_data_property_or_throw(vm.names.signDisplay, PrimitiveString::create(vm, "never"_utf16_fly_string)));
     }
 
     // 9. Perform ! CreateDataPropertyOrThrow(nfOpts, "useGrouping", false).
@@ -412,7 +412,7 @@ Vector<DurationFormatPart> format_numeric_hours(VM& vm, DurationFormat const& du
 
     for (auto& part : hours_parts) {
         // a. Append the Record { [[Type]]: part.[[Type]], [[Value]]: part.[[Value]], [[Unit]]: "hour" } to result.
-        result.unchecked_append({ .type = part.type, .value = move(part.value), .unit = "hour"sv });
+        result.unchecked_append({ .type = move(part.type), .value = move(part.value), .unit = "hour"_utf16 });
     }
 
     // 13. Return result.
@@ -433,7 +433,7 @@ Vector<DurationFormatPart> format_numeric_minutes(VM& vm, DurationFormat const&
         auto separator = duration_format.hour_minute_separator();
 
         // b. Append the Record { [[Type]]: "literal", [[Value]]: separator, [[Unit]]: EMPTY } to result.
-        result.append({ .type = "literal"sv, .value = move(separator), .unit = {} });
+        result.append({ .type = "literal"_utf16, .value = move(separator), .unit = {} });
     }
 
     // 3. Let minutesStyle be durationFormat.[[MinutesOptions]].[[Style]].
@@ -460,7 +460,7 @@ Vector<DurationFormatPart> format_numeric_minutes(VM& vm, DurationFormat const&
     // 9. If signDisplayed is false, then
     if (!sign_displayed) {
         // a. Perform ! CreateDataPropertyOrThrow(nfOpts, "signDisplay", "never").
-        MUST(number_format_options->create_data_property_or_throw(vm.names.signDisplay, PrimitiveString::create(vm, "never"sv)));
+        MUST(number_format_options->create_data_property_or_throw(vm.names.signDisplay, PrimitiveString::create(vm, "never"_utf16_fly_string)));
     }
 
     // 10. Perform ! CreateDataPropertyOrThrow(nfOpts, "useGrouping", false).
@@ -477,7 +477,7 @@ Vector<DurationFormatPart> format_numeric_minutes(VM& vm, DurationFormat const&
 
     for (auto& part : minutes_parts) {
         // a. Append the Record { [[Type]]: part.[[Type]], [[Value]]: part.[[Value]], [[Unit]]: "minute" } to result.
-        result.unchecked_append({ .type = part.type, .value = move(part.value), .unit = "minute"sv });
+        result.unchecked_append({ .type = move(part.type), .value = move(part.value), .unit = "minute"_utf16 });
     }
 
     // 14. Return result.
@@ -498,7 +498,7 @@ Vector<DurationFormatPart> format_numeric_seconds(VM& vm, DurationFormat const&
         auto separator = duration_format.minute_second_separator();
 
         // b. Append the Record { [[Type]]: "literal", [[Value]]: separator, [[Unit]]: EMPTY } to result.
-        result.append({ .type = "literal"sv, .value = move(separator), .unit = {} });
+        result.append({ .type = "literal"_utf16, .value = move(separator), .unit = {} });
     }
 
     // 3. Let secondsStyle be durationFormat.[[SecondsOptions]].[[Style]].
@@ -525,7 +525,7 @@ Vector<DurationFormatPart> format_numeric_seconds(VM& vm, DurationFormat const&
     // 9. If signDisplayed is false, then
     if (!sign_displayed) {
         // a. Perform ! CreateDataPropertyOrThrow(nfOpts, "signDisplay", "never").
-        MUST(number_format_options->create_data_property_or_throw(vm.names.signDisplay, PrimitiveString::create(vm, "never"sv)));
+        MUST(number_format_options->create_data_property_or_throw(vm.names.signDisplay, PrimitiveString::create(vm, "never"_utf16_fly_string)));
     }
 
     // 10. Perform ! CreateDataPropertyOrThrow(nfOpts, "useGrouping", false).
@@ -552,7 +552,7 @@ Vector<DurationFormatPart> format_numeric_seconds(VM& vm, DurationFormat const&
     }
 
     // 14. Perform ! CreateDataPropertyOrThrow(nfOpts, "roundingMode", "trunc").
-    MUST(number_format_options->create_data_property_or_throw(vm.names.roundingMode, PrimitiveString::create(vm, "trunc"sv)));
+    MUST(number_format_options->create_data_property_or_throw(vm.names.roundingMode, PrimitiveString::create(vm, "trunc"_utf16_fly_string)));
 
     // 15. Let nf be ! Construct(%Intl.NumberFormat%, « durationFormat.[[Locale]], nfOpts »).
     auto number_format = construct_number_format(vm, duration_format, number_format_options);
@@ -565,7 +565,7 @@ Vector<DurationFormatPart> format_numeric_seconds(VM& vm, DurationFormat const&
 
     for (auto& part : seconds_parts) {
         // a. Append the Record { [[Type]]: part.[[Type]], [[Value]]: part.[[Value]], [[Unit]]: "second" } to result.
-        result.unchecked_append({ .type = part.type, .value = move(part.value), .unit = "second"sv });
+        result.unchecked_append({ .type = move(part.type), .value = move(part.value), .unit = "second"_utf16 });
     }
 
     // 18. Return result.
@@ -690,7 +690,7 @@ Vector<DurationFormatPart> format_numeric_units(VM& vm, DurationFormat const& du
     // 18. If secondsFormatted is true, then
     if (seconds_formatted) {
         // a. Let secondsParts be FormatNumericSeconds(durationFormat, secondsValue, minutesFormatted, signDisplayed).
-        auto seconds_value_mv = MathematicalValue { Utf16String::from_utf8(seconds_value.to_string(9)) };
+        auto seconds_value_mv = MathematicalValue { seconds_value.to_utf16_string(9) };
         auto seconds_parts = format_numeric_seconds(vm, duration_format, seconds_value_mv, minutes_formatted, sign_displayed);
 
         // b. Set numericPartsList to the list-concatenation of numericPartsList and secondsParts.
@@ -718,7 +718,7 @@ Vector<DurationFormatPart> list_format_parts(VM& vm, DurationFormat const& durat
     auto list_format_options = Object::create(realm, nullptr);
 
     // 2. Perform ! CreateDataPropertyOrThrow(lfOpts, "type", "unit").
-    MUST(list_format_options->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, "unit"sv)));
+    MUST(list_format_options->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, "unit"_utf16_fly_string)));
 
     // 3. Let listStyle be durationFormat.[[Style]].
     auto list_style = duration_format.style();
@@ -731,7 +731,7 @@ Vector<DurationFormatPart> list_format_parts(VM& vm, DurationFormat const& durat
 
     // 5. Perform ! CreateDataPropertyOrThrow(lfOpts, "style", listStyle).
     auto locale_list_style = Unicode::style_to_string(static_cast<Unicode::Style>(list_style));
-    MUST(list_format_options->create_data_property_or_throw(vm.names.style, PrimitiveString::create(vm, locale_list_style)));
+    MUST(list_format_options->create_data_property_or_throw(vm.names.style, PrimitiveString::create(vm, move(locale_list_style))));
 
     // 6. Let lf be ! Construct(%Intl.ListFormat%, « durationFormat.[[Locale]], lfOpts »).
     auto list_format = construct_list_format(vm, duration_format, list_format_options);
@@ -792,7 +792,7 @@ Vector<DurationFormatPart> list_format_parts(VM& vm, DurationFormat const& durat
             VERIFY(list_part.type == "literal"sv);
 
             // ii. Append the Record { [[Type]]: "literal", [[Value]]: listPart.[[Value]], [[Unit]]: empty } to flattenedPartsList.
-            flattened_parts_list.append({ .type = "literal"sv, .value = move(list_part.value), .unit = {} });
+            flattened_parts_list.append({ .type = "literal"_utf16, .value = move(list_part.value), .unit = {} });
         }
     }
 
@@ -876,7 +876,7 @@ Vector<DurationFormatPart> partition_duration_format_pattern(VM& vm, DurationFor
                 }
 
                 // 5. Perform ! CreateDataPropertyOrThrow(nfOpts, "roundingMode", "trunc").
-                MUST(number_format_options->create_data_property_or_throw(vm.names.roundingMode, PrimitiveString::create(vm, "trunc"sv)));
+                MUST(number_format_options->create_data_property_or_throw(vm.names.roundingMode, PrimitiveString::create(vm, "trunc"_utf16_fly_string)));
 
                 // 6. Set numericUnitFound to true.
                 numeric_unit_found = true;
@@ -884,7 +884,7 @@ Vector<DurationFormatPart> partition_duration_format_pattern(VM& vm, DurationFor
 
             // iii. If display is "always" or value is not 0, then
             if (display == DurationFormat::Display::Always || !value.is_zero()) {
-                auto value_mv = MathematicalValue { Utf16String::from_utf8(value.to_string(9)) };
+                auto value_mv = MathematicalValue { value.to_utf16_string(9) };
 
                 // 1. Perform ! CreateDataPropertyOrThrow(nfOpts, "numberingSystem", durationFormat.[[NumberingSystem]]).
                 MUST(number_format_options->create_data_property_or_throw(vm.names.numberingSystem, PrimitiveString::create(vm, duration_format.numbering_system())));
@@ -901,18 +901,18 @@ Vector<DurationFormatPart> partition_duration_format_pattern(VM& vm, DurationFor
                 // 3. Else,
                 else {
                     // a. Perform ! CreateDataPropertyOrThrow(nfOpts, "signDisplay", "never").
-                    MUST(number_format_options->create_data_property_or_throw(vm.names.signDisplay, PrimitiveString::create(vm, "never"sv)));
+                    MUST(number_format_options->create_data_property_or_throw(vm.names.signDisplay, PrimitiveString::create(vm, "never"_utf16_fly_string)));
                 }
 
                 // 3. Perform ! CreateDataPropertyOrThrow(nfOpts, "style", "unit").
-                MUST(number_format_options->create_data_property_or_throw(vm.names.style, PrimitiveString::create(vm, "unit"sv)));
+                MUST(number_format_options->create_data_property_or_throw(vm.names.style, PrimitiveString::create(vm, "unit"_utf16_fly_string)));
 
                 // 4. Perform ! CreateDataPropertyOrThrow(nfOpts, "unit", numberFormatUnit).
                 MUST(number_format_options->create_data_property_or_throw(vm.names.unit, PrimitiveString::create(vm, number_format_unit.as_string())));
 
                 // 5. Perform ! CreateDataPropertyOrThrow(nfOpts, "unitDisplay", style).
                 auto locale_style = Unicode::style_to_string(static_cast<Unicode::Style>(style));
-                MUST(number_format_options->create_data_property_or_throw(vm.names.unitDisplay, PrimitiveString::create(vm, locale_style)));
+                MUST(number_format_options->create_data_property_or_throw(vm.names.unitDisplay, PrimitiveString::create(vm, move(locale_style))));
 
                 // 6. Let nf be ! Construct(%Intl.NumberFormat%, « durationFormat.[[Locale]], nfOpts »).
                 auto number_format = construct_number_format(vm, duration_format, number_format_options);
@@ -925,10 +925,11 @@ Vector<DurationFormatPart> partition_duration_format_pattern(VM& vm, DurationFor
 
                 // 10. For each Record { [[Type]], [[Value]] } part of parts, do
                 list.ensure_capacity(parts.size());
+                auto unit = number_format_unit.as_string().to_utf16_string();
 
                 for (auto& part : parts) {
                     // a. Append the Record { [[Type]]: part.[[Type]], [[Value]]: part.[[Value]], [[Unit]]: numberFormatUnit } to list.
-                    list.unchecked_append({ .type = part.type, .value = move(part.value), .unit = number_format_unit.as_string().view() });
+                    list.unchecked_append({ .type = move(part.type), .value = move(part.value), .unit = unit });
                 }
 
                 // 11. Append list to result.
diff --git a/Libraries/LibJS/Runtime/Intl/DurationFormat.h b/Libraries/LibJS/Runtime/Intl/DurationFormat.h
index 8da8fc81f9..7aea4f875b 100644
--- a/Libraries/LibJS/Runtime/Intl/DurationFormat.h
+++ b/Libraries/LibJS/Runtime/Intl/DurationFormat.h
@@ -8,7 +8,7 @@
 #pragma once
 
 #include <AK/Array.h>
-#include <AK/String.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 #include <LibCrypto/BigFraction/BigFraction.h>
 #include <LibJS/Runtime/Intl/IntlObject.h>
@@ -29,7 +29,7 @@ public:
         Digital,
     };
     static Style style_from_string(Utf16View style);
-    static StringView style_to_string(Style);
+    static Utf16String style_to_string(Style);
 
     enum class ValueStyle {
         Long,
@@ -40,7 +40,7 @@ public:
         Fractional,
     };
     static ValueStyle value_style_from_string(Utf16View);
-    static StringView value_style_to_string(ValueStyle);
+    static Utf16String value_style_to_string(ValueStyle);
 
     static_assert(to_underlying(ValueStyle::Long) == to_underlying(Unicode::Style::Long));
     static_assert(to_underlying(ValueStyle::Short) == to_underlying(Unicode::Style::Short));
@@ -51,7 +51,7 @@ public:
         Always,
     };
     static Display display_from_string(Utf16View display);
-    static StringView display_to_string(Display);
+    static Utf16String display_to_string(Display);
 
     enum class Unit {
         Years,
@@ -74,14 +74,14 @@ public:
 
     virtual ~DurationFormat() override = default;
 
-    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<Utf16View> relevant_extension_keys() const override;
     virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
 
-    void set_locale(String locale) { m_locale = move(locale); }
-    String const& locale() const { return m_locale; }
+    void set_locale(Utf16String locale) { m_locale = move(locale); }
+    Utf16String const& locale() const { return m_locale; }
 
-    void set_numbering_system(String numbering_system) { m_numbering_system = move(numbering_system); }
-    String const& numbering_system() const { return m_numbering_system; }
+    void set_numbering_system(Utf16String numbering_system) { m_numbering_system = move(numbering_system); }
+    Utf16String const& numbering_system() const { return m_numbering_system; }
 
     void set_hour_minute_separator(Utf16String hour_minute_separator) { m_hour_minute_separator = move(hour_minute_separator); }
     Utf16String const& hour_minute_separator() const { return m_hour_minute_separator; }
@@ -91,7 +91,7 @@ public:
 
     void set_style(Utf16View style) { m_style = style_from_string(style); }
     Style style() const { return m_style; }
-    StringView style_string() const { return style_to_string(m_style); }
+    Utf16String style_string() const { return style_to_string(m_style); }
 
     void set_years_options(DurationUnitOptions years_options) { m_years_options = years_options; }
     DurationUnitOptions years_options() const { return m_years_options; }
@@ -130,8 +130,8 @@ public:
 private:
     explicit DurationFormat(Object& prototype);
 
-    String m_locale;                       // [[Locale]]
-    String m_numbering_system;             // [[NumberingSystem]]
+    Utf16String m_locale;                  // [[Locale]]
+    Utf16String m_numbering_system;        // [[NumberingSystem]]
     Utf16String m_hour_minute_separator;   // [[HourMinutesSeparator]]
     Utf16String m_minute_second_separator; // [[MinutesSecondsSeparator]]
 
@@ -178,9 +178,9 @@ static constexpr auto duration_instances_components = to_array<DurationInstanceC
 });
 
 struct DurationFormatPart {
-    StringView type;
+    Utf16String type;
     Utf16String value;
-    Utf16View unit;
+    Utf16String unit;
 };
 
 ThrowCompletionOr<DurationFormat::DurationUnitOptions> get_duration_unit_options(VM&, DurationFormat::Unit unit, Object const& options, DurationFormat::Style base_style, ReadonlySpan<StringView> styles_list, DurationFormat::ValueStyle digital_base, Optional<DurationFormat::ValueStyle> previous_style, bool two_digit_hours);
diff --git a/Libraries/LibJS/Runtime/Intl/DurationFormatConstructor.cpp b/Libraries/LibJS/Runtime/Intl/DurationFormatConstructor.cpp
index c904f21c0e..89930e29c0 100644
--- a/Libraries/LibJS/Runtime/Intl/DurationFormatConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Intl/DurationFormatConstructor.cpp
@@ -67,7 +67,7 @@ ThrowCompletionOr<GC::Ref<Object>> DurationFormatConstructor::construct(Function
     // 7. Let resolvedLocaleData be r.[[LocaleData]].
 
     // 8. Let digitalFormat be resolvedLocaleData.[[DigitalFormat]].
-    auto digital_format = Unicode::digital_format(result.icu_locale);
+    auto digital_format = Unicode::digital_format(result.icu_locale.utf16_view());
 
     // 9. Set durationFormat.[[HourMinuteSeparator]] to digitalFormat.[[HourMinuteSeparator]].
     duration_format->set_hour_minute_separator(move(digital_format.hours_minutes_separator));
@@ -76,11 +76,11 @@ ThrowCompletionOr<GC::Ref<Object>> DurationFormatConstructor::construct(Function
     duration_format->set_minute_second_separator(move(digital_format.minutes_seconds_separator));
 
     // 11. Set durationFormat.[[NumberingSystem]] to r.[[nu]].
-    if (auto* resolved_numbering_system = result.nu.get_pointer<String>())
+    if (auto* resolved_numbering_system = result.nu.get_pointer<Utf16String>())
         duration_format->set_numbering_system(move(*resolved_numbering_system));
 
     // 12. Let style be ? GetOption(options, "style", STRING, « "long", "short", "narrow", "digital" », "short").
-    auto style = TRY(get_option(vm, *options, vm.names.style, OptionType::String, { "long"sv, "short"sv, "narrow"sv, "digital"sv }, "short"sv));
+    auto style = TRY(get_option(vm, *options, vm.names.style, OptionType::String, { "long"sv, "short"sv, "narrow"sv, "digital"sv }, u"short"sv));
 
     // 13. Set durationFormat.[[Style]] to style.
     duration_format->set_style(style.as_string().utf16_string_view());
diff --git a/Libraries/LibJS/Runtime/Intl/DurationFormatPrototype.cpp b/Libraries/LibJS/Runtime/Intl/DurationFormatPrototype.cpp
index faa379a8e1..df2455b0f4 100644
--- a/Libraries/LibJS/Runtime/Intl/DurationFormatPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Intl/DurationFormatPrototype.cpp
@@ -29,7 +29,7 @@ void DurationFormatPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 13.3.5 Intl.DurationFormat.prototype [ %Symbol.toStringTag% ], https://tc39.es/ecma402/#sec-Intl.DurationFormat.prototype-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.DurationFormat"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.DurationFormat"_utf16_fly_string), Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(realm, vm.names.resolvedOptions, resolved_options, 0, attr);
@@ -77,11 +77,13 @@ JS_DEFINE_NATIVE_FUNCTION(DurationFormatPrototype::resolved_options)
             }
 
             // 5. Perform ! CreateDataPropertyOrThrow(options, p, style).
-            MUST(options->create_data_property_or_throw(property, PrimitiveString::create(vm, DurationFormat::value_style_to_string(style))));
+            auto style_string = DurationFormat::value_style_to_string(style);
+            MUST(options->create_data_property_or_throw(property, PrimitiveString::create(vm, move(style_string))));
 
             // 6. Set p to the string-concatenation of p and "Display".
             // 7. Set v to v.[[Display]].
-            MUST(options->create_data_property_or_throw(*display_property, PrimitiveString::create(vm, DurationFormat::display_to_string(value.display))));
+            auto display_string = DurationFormat::display_to_string(value.display);
+            MUST(options->create_data_property_or_throw(*display_property, PrimitiveString::create(vm, move(display_string))));
         } else {
             // iv. Perform ! CreateDataPropertyOrThrow(options, p, v).
             MUST(options->create_data_property_or_throw(property, PrimitiveString::create(vm, move(value))));
@@ -162,14 +164,14 @@ JS_DEFINE_NATIVE_FUNCTION(DurationFormatPrototype::format_to_parts)
         auto object = Object::create(realm, realm.intrinsics().object_prototype());
 
         // b. Perform ! CreateDataPropertyOrThrow(obj, "type", part.[[Type]]).
-        MUST(object->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, part.type)));
+        MUST(object->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, move(part.type))));
 
         // c. Perform ! CreateDataPropertyOrThrow(obj, "value", part.[[Value]]).
         MUST(object->create_data_property_or_throw(vm.names.value, PrimitiveString::create(vm, move(part.value))));
 
         // d. If part.[[Unit]] is not empty, perform ! CreateDataPropertyOrThrow(obj, "unit", part.[[Unit]]).
         if (!part.unit.is_empty())
-            MUST(object->create_data_property_or_throw(vm.names.unit, PrimitiveString::create(vm, part.unit)));
+            MUST(object->create_data_property_or_throw(vm.names.unit, PrimitiveString::create(vm, move(part.unit))));
 
         // e. Perform ! CreateDataPropertyOrThrow(result, ! ToString(n), obj).
         MUST(result->create_data_property_or_throw(n, object));
diff --git a/Libraries/LibJS/Runtime/Intl/Intl.cpp b/Libraries/LibJS/Runtime/Intl/Intl.cpp
index 58ab214c26..95315ee923 100644
--- a/Libraries/LibJS/Runtime/Intl/Intl.cpp
+++ b/Libraries/LibJS/Runtime/Intl/Intl.cpp
@@ -45,7 +45,7 @@ void Intl::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 8.1.1 Intl[ @@toStringTag ], https://tc39.es/ecma402/#sec-Intl-toStringTag
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl"_utf16_fly_string), Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_intrinsic_accessor(vm.names.Collator, attr, [](auto& realm) -> Value { return realm.intrinsics().intl_collator_constructor(); });
@@ -73,24 +73,20 @@ JS_DEFINE_NATIVE_FUNCTION(Intl::get_canonical_locales)
     // 1. Let ll be ? CanonicalizeLocaleList(locales).
     auto locale_list = TRY(canonicalize_locale_list(vm, locales));
 
-    GC::RootVector<Value> marked_locale_list;
-    marked_locale_list.ensure_capacity(locale_list.size());
-
-    for (auto& locale : locale_list)
-        marked_locale_list.unchecked_append(PrimitiveString::create(vm, move(locale)));
-
     // 2. Return CreateArrayFromList(ll).
-    return Array::create_from(realm, marked_locale_list);
+    return Array::create_from<Utf16String>(realm, locale_list, [&vm](auto const& locale) {
+        return PrimitiveString::create(vm, locale);
+    });
 }
 
 // 6.5.4 AvailablePrimaryTimeZoneIdentifiers ( ), https://tc39.es/ecma402/#sec-availableprimarytimezoneidentifiers
-static Vector<String> available_primary_time_zone_identifiers()
+static Vector<Utf16String> available_primary_time_zone_identifiers()
 {
     // 1. Let records be AvailableNamedTimeZoneIdentifiers().
     auto const& records = available_named_time_zone_identifiers();
 
     // 2. Let result be a new empty List.
-    Vector<String> result;
+    Vector<Utf16String> result;
 
     // 3. For each element timeZoneIdentifierRecord of records, do
     for (auto const& time_zone_identifier_record : records) {
@@ -113,7 +109,7 @@ JS_DEFINE_NATIVE_FUNCTION(Intl::supported_values_of)
     // 1. Let key be ? ToString(key).
     auto key = TRY(vm.argument(0).to_utf16_string(vm));
 
-    Optional<Variant<ReadonlySpan<StringView>, ReadonlySpan<String>>> list;
+    Optional<ReadonlySpan<Utf16String>> list;
 
     // 2. If key is "calendar", then
     if (key == "calendar"sv) {
@@ -138,13 +134,20 @@ JS_DEFINE_NATIVE_FUNCTION(Intl::supported_values_of)
     // 6. Else if key is "timeZone", then
     else if (key == "timeZone"sv) {
         // a. Let list be ! AvailablePrimaryTimeZoneIdentifiers( ).
-        static NeverDestroyed<Vector<String>> time_zones { available_primary_time_zone_identifiers() };
+        static NeverDestroyed<Vector<Utf16String>> time_zones { available_primary_time_zone_identifiers() };
         list = time_zones->span();
     }
     // 7. Else if key is "unit", then
     else if (key == "unit"sv) {
         // a. Let list be ! AvailableCanonicalUnits( ).
-        static NeverDestroyed<Vector<StringView>> units { sanctioned_single_unit_identifiers() };
+        static NeverDestroyed<Vector<Utf16String>> units { [] {
+            Vector<Utf16String> units;
+            auto sanctioned_units = sanctioned_single_unit_identifiers();
+            units.ensure_capacity(sanctioned_units.size());
+            for (auto unit : sanctioned_units)
+                units.unchecked_append(Utf16String::from_utf16(unit));
+            return units;
+        }() };
         list = units->span();
     }
     // 8. Else,
@@ -154,10 +157,8 @@ JS_DEFINE_NATIVE_FUNCTION(Intl::supported_values_of)
     }
 
     // 9. Return CreateArrayFromList( list ).
-    return list->visit([&]<typename T>(ReadonlySpan<T> list) {
-        return Array::create_from<T>(realm, list, [&](auto value) {
-            return PrimitiveString::create(vm, value);
-        });
+    return Array::create_from<Utf16String>(realm, *list, [&](auto const& value) {
+        return PrimitiveString::create(vm, value);
     });
 }
 
diff --git a/Libraries/LibJS/Runtime/Intl/IntlObject.h b/Libraries/LibJS/Runtime/Intl/IntlObject.h
index 759113bee1..8d2adb8af3 100644
--- a/Libraries/LibJS/Runtime/Intl/IntlObject.h
+++ b/Libraries/LibJS/Runtime/Intl/IntlObject.h
@@ -8,6 +8,7 @@
 
 #include <AK/Span.h>
 #include <AK/StringView.h>
+#include <AK/Utf16View.h>
 #include <LibJS/Runtime/AbstractOperations.h>
 #include <LibJS/Runtime/Object.h>
 #include <LibJS/Runtime/PropertyKey.h>
@@ -16,7 +17,7 @@ namespace JS::Intl {
 
 // https://tc39.es/ecma402/#resolution-option-descriptor
 struct ResolutionOptionDescriptor {
-    StringView key;
+    Utf16View key;
     PropertyKey property;
     OptionType type { OptionType::String };
     ReadonlySpan<StringView> values {};
@@ -26,7 +27,7 @@ class IntlObject : public Object {
     JS_OBJECT(IntlObject, Object);
 
 public:
-    virtual ReadonlySpan<StringView> relevant_extension_keys() const = 0;
+    virtual ReadonlySpan<Utf16View> relevant_extension_keys() const = 0;
     virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const = 0;
 
 protected:
diff --git a/Libraries/LibJS/Runtime/Intl/ListFormat.cpp b/Libraries/LibJS/Runtime/Intl/ListFormat.cpp
index 02d8600bf2..b923481789 100644
--- a/Libraries/LibJS/Runtime/Intl/ListFormat.cpp
+++ b/Libraries/LibJS/Runtime/Intl/ListFormat.cpp
@@ -21,7 +21,7 @@ ListFormat::ListFormat(Object& prototype)
 }
 
 // 14.2.3 Internal slots, https://tc39.es/ecma402/#sec-Intl.ListFormat-internal-slots
-ReadonlySpan<StringView> ListFormat::relevant_extension_keys() const
+ReadonlySpan<Utf16View> ListFormat::relevant_extension_keys() const
 {
     // The value of the [[RelevantExtensionKeys]] internal slot is « ».
     return {};
@@ -71,7 +71,7 @@ GC::Ref<Array> format_list_to_parts(VM& vm, ListFormat const& list_format, Reado
         auto object = Object::create(realm, realm.intrinsics().object_prototype());
 
         // b. Perform ! CreateDataPropertyOrThrow(O, "type", part.[[Type]]).
-        MUST(object->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, part.type)));
+        MUST(object->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, move(part.type))));
 
         // c. Perform ! CreateDataPropertyOrThrow(O, "value", part.[[Value]]).
         MUST(object->create_data_property_or_throw(vm.names.value, PrimitiveString::create(vm, move(part.value))));
diff --git a/Libraries/LibJS/Runtime/Intl/ListFormat.h b/Libraries/LibJS/Runtime/Intl/ListFormat.h
index 1cdea60398..00dec81c2b 100644
--- a/Libraries/LibJS/Runtime/Intl/ListFormat.h
+++ b/Libraries/LibJS/Runtime/Intl/ListFormat.h
@@ -6,8 +6,8 @@
 
 #pragma once
 
-#include <AK/String.h>
 #include <AK/StringView.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 #include <AK/Vector.h>
 #include <LibJS/Runtime/Intl/IntlObject.h>
@@ -30,21 +30,19 @@ public:
 
     virtual ~ListFormat() override = default;
 
-    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<Utf16View> relevant_extension_keys() const override;
     virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
 
-    String const& locale() const { return m_locale; }
-    void set_locale(String locale) { m_locale = move(locale); }
+    Utf16String const& locale() const { return m_locale; }
+    void set_locale(Utf16String locale) { m_locale = move(locale); }
 
     Unicode::ListFormatType type() const { return m_type; }
-    void set_type(StringView type) { m_type = Unicode::list_format_type_from_string(type); }
     void set_type(Utf16View type) { m_type = Unicode::list_format_type_from_string(type); }
-    StringView type_string() const { return Unicode::list_format_type_to_string(m_type); }
+    Utf16String type_string() const { return Unicode::list_format_type_to_string(m_type); }
 
     Unicode::Style style() const { return m_style; }
-    void set_style(StringView style) { m_style = Unicode::style_from_string(style); }
     void set_style(Utf16View style) { m_style = Unicode::style_from_string(style); }
-    StringView style_string() const { return Unicode::style_to_string(m_style); }
+    Utf16String style_string() const { return Unicode::style_to_string(m_style); }
 
     Unicode::ListFormat const& formatter() const { return *m_formatter; }
     void set_formatter(NonnullOwnPtr<Unicode::ListFormat> formatter) { m_formatter = move(formatter); }
@@ -52,7 +50,7 @@ public:
 private:
     explicit ListFormat(Object& prototype);
 
-    String m_locale;                                                         // [[Locale]]
+    Utf16String m_locale;                                                    // [[Locale]]
     Unicode::ListFormatType m_type { Unicode::ListFormatType::Conjunction }; // [[Type]]
     Unicode::Style m_style { Unicode::Style::Long };                         // [[Style]]
 
diff --git a/Libraries/LibJS/Runtime/Intl/ListFormatConstructor.cpp b/Libraries/LibJS/Runtime/Intl/ListFormatConstructor.cpp
index d8edc70336..6fec1a0df3 100644
--- a/Libraries/LibJS/Runtime/Intl/ListFormatConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Intl/ListFormatConstructor.cpp
@@ -63,13 +63,13 @@ ThrowCompletionOr<GC::Ref<Object>> ListFormatConstructor::construct(FunctionObje
     list_format->set_locale(move(result.locale));
 
     // 7. Let type be ? GetOption(options, "type", string, « "conjunction", "disjunction", "unit" », "conjunction").
-    auto type = TRY(get_option(vm, *options, vm.names.type, OptionType::String, { "conjunction"sv, "disjunction"sv, "unit"sv }, "conjunction"sv));
+    auto type = TRY(get_option(vm, *options, vm.names.type, OptionType::String, { "conjunction"sv, "disjunction"sv, "unit"sv }, u"conjunction"sv));
 
     // 8. Set listFormat.[[Type]] to type.
     list_format->set_type(type.as_string().utf16_string_view());
 
     // 9. Let style be ? GetOption(options, "style", string, « "long", "short", "narrow" », "long").
-    auto style = TRY(get_option(vm, *options, vm.names.style, OptionType::String, { "long"sv, "short"sv, "narrow"sv }, "long"sv));
+    auto style = TRY(get_option(vm, *options, vm.names.style, OptionType::String, { "long"sv, "short"sv, "narrow"sv }, u"long"sv));
 
     // 10. Set listFormat.[[Style]] to style.
     list_format->set_style(style.as_string().utf16_string_view());
@@ -78,7 +78,7 @@ ThrowCompletionOr<GC::Ref<Object>> ListFormatConstructor::construct(FunctionObje
     // 12. Let dataLocaleTypes be resolvedLocaleData.[[<type>]].
     // 13. Set listFormat.[[Templates]] to dataLocaleTypes.[[<style>]].
     auto formatter = Unicode::ListFormat::create(
-        list_format->locale(),
+        result.icu_locale.utf16_view().bytes(),
         list_format->type(),
         list_format->style());
     list_format->set_formatter(move(formatter));
diff --git a/Libraries/LibJS/Runtime/Intl/ListFormatPrototype.cpp b/Libraries/LibJS/Runtime/Intl/ListFormatPrototype.cpp
index 2c7c1c7e11..e547b523f2 100644
--- a/Libraries/LibJS/Runtime/Intl/ListFormatPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Intl/ListFormatPrototype.cpp
@@ -27,7 +27,7 @@ void ListFormatPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 14.3.5 Intl.ListFormat.prototype [ %Symbol.toStringTag% ], https://tc39.es/ecma402/#sec-Intl.ListFormat.prototype-toStringTag
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.ListFormat"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.ListFormat"_utf16_fly_string), Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(realm, vm.names.resolvedOptions, resolved_options, 0, attr);
diff --git a/Libraries/LibJS/Runtime/Intl/Locale.cpp b/Libraries/LibJS/Runtime/Intl/Locale.cpp
index 3c3452c551..0eeaedc485 100644
--- a/Libraries/LibJS/Runtime/Intl/Locale.cpp
+++ b/Libraries/LibJS/Runtime/Intl/Locale.cpp
@@ -15,7 +15,7 @@ namespace JS::Intl {
 
 GC_DEFINE_ALLOCATOR(Locale);
 
-GC::Ref<Locale> Locale::create(Realm& realm, GC::Ref<Locale> source_locale, String locale_tag)
+GC::Ref<Locale> Locale::create(Realm& realm, GC::Ref<Locale> source_locale, Utf16String locale_tag)
 {
     auto locale = realm.create<Locale>(realm.intrinsics().intl_locale_prototype());
 
@@ -38,11 +38,11 @@ Locale::Locale(Object& prototype)
 
 Unicode::LocaleID const& Locale::locale_id() const
 {
-    return m_cached_locale_id.ensure([&] { return Unicode::parse_unicode_locale_id(locale()); });
+    return m_cached_locale_id.ensure([&] { return Unicode::parse_unicode_locale_id(locale().utf16_view()); });
 }
 
 // 15.5.5 GetLocaleVariants ( locale ), https://tc39.es/ecma402/#sec-getlocalevariants
-Optional<String> get_locale_variants(Unicode::LocaleID const& locale)
+Optional<Utf16String> get_locale_variants(Unicode::LocaleID const& locale)
 {
     // 1. Let baseName be GetLocaleBaseName(locale).
     auto const& base_name = locale.language_id;
@@ -57,7 +57,7 @@ Optional<String> get_locale_variants(Unicode::LocaleID const& locale)
         return {};
 
     // 4. Return the substring of variants from 1.
-    return MUST(String::join("-"sv, base_name.variants));
+    return Utf16String::join("-"sv, base_name.variants);
 }
 
 // 15.5.9 CalendarsOfLocale ( loc ), https://tc39.es/ecma402/#sec-calendarsoflocale
@@ -82,10 +82,10 @@ GC::Ref<Array> calendars_of_locale(VM& vm, Locale const& locale_object)
     //    in common use for date and time formatting in lookupRegion. The list is empty if no calendar preference data
     //    for lookupRegion is available.
     // 8. If list is empty, set list to « "gregory" ».
-    auto list = Unicode::available_calendars(locale_object.locale());
+    auto list = Unicode::available_calendars(locale_object.locale().utf16_view());
 
     // 9. Return CreateArrayFromList(list).
-    return Array::create_from<String>(realm, list, [&vm](auto const& value) {
+    return Array::create_from<Utf16String>(realm, list, [&vm](auto const& value) {
         return PrimitiveString::create(vm, value);
     });
 }
@@ -115,10 +115,10 @@ GC::Ref<Array> collations_of_locale(VM& vm, Locale const& locale_object)
     // 4. Else,
     //     a. Let list be « "emoji", "eor" ».
     // 5. Let sorted be a copy of list, sorted according to lexicographic code unit order.
-    auto list = Unicode::available_collations(locale_object.locale());
+    auto list = Unicode::available_collations(locale_object.locale().utf16_view());
 
     // 6. Return CreateArrayFromList(sorted).
-    return Array::create_from<String>(realm, list, [&vm](auto const& value) {
+    return Array::create_from<Utf16String>(realm, list, [&vm](auto const& value) {
         return PrimitiveString::create(vm, value);
     });
 }
@@ -143,10 +143,10 @@ GC::Ref<Array> hour_cycles_of_locale(VM& vm, Locale const& locale_object)
     //     a. Let lookupRegion be region.
     // 7. Let list be a List of unique hour cycle identifiers, which must be lower case String values indicating either the 12-hour format ("h11", "h12") or the 24-hour format ("h23", "h24"), sorted in descending preference of those in common use for date and time formatting in lookupRegion. The list is empty if no time data for lookupRegion is available.
     // 8. If list is empty, set list to « "h23" ».
-    auto list = Unicode::available_hour_cycles(locale_object.locale());
+    auto list = Unicode::available_hour_cycles(locale_object.locale().utf16_view());
 
     // 9. Return CreateArrayFromList(list).
-    return Array::create_from<String>(realm, list, [&vm](auto const& value) {
+    return Array::create_from<Utf16String>(realm, list, [&vm](auto const& value) {
         return PrimitiveString::create(vm, value);
     });
 }
@@ -170,10 +170,10 @@ GC::Ref<Array> numbering_systems_of_locale(VM& vm, Locale const& locale_object)
     //     d. Let list be « numberingSystems[0] ».
     // 4. Else,
     //     a. Let list be « "latn" ».
-    auto list = Unicode::available_number_systems(locale_object.locale());
+    auto list = Unicode::available_number_systems(locale_object.locale().utf16_view());
 
     // 5. Return CreateArrayFromList(list).
-    return Array::create_from<String>(realm, list, [&vm](auto const& value) {
+    return Array::create_from<Utf16String>(realm, list, [&vm](auto const& value) {
         return PrimitiveString::create(vm, value);
     });
 }
@@ -193,16 +193,16 @@ Value time_zones_of_locale(VM& vm, Locale const& locale_object)
     // 3. Let list be a List of unique canonical time zone identifiers, which must be String values indicating a
     //    canonical Zone name of the IANA Time Zone Database, of those in common use in region. The list is empty if no
     //    time zones are commonly used in region. The list is sorted according to lexicographic code unit order.
-    auto list = Unicode::available_time_zones_in_region(*region);
+    auto list = Unicode::available_time_zones_in_region(region->utf16_view());
 
     // 4. Return CreateArrayFromList( list ).
-    return Array::create_from<String>(realm, list, [&vm](auto const& value) {
+    return Array::create_from<Utf16String>(realm, list, [&vm](auto const& value) {
         return PrimitiveString::create(vm, value);
     });
 }
 
 // 15.5.14 TextDirectionOfLocale ( loc ), https://tc39.es/ecma402/#sec-textdirectionoflocale
-StringView text_direction_of_locale(Locale const& locale_object)
+Utf16View text_direction_of_locale(Locale const& locale_object)
 {
     // 1. Let locale be loc.[[Locale]].
     auto const& locale = locale_object.locale();
@@ -218,29 +218,29 @@ StringView text_direction_of_locale(Locale const& locale_object)
     // 5. If the default general ordering of characters within a line in script is left-to-right, return "ltr".
     // 6. Return undefined.
     // FIXME: ICU does not provide a method to determine if a locale is neither rtl nor ltr.
-    return Unicode::is_locale_character_ordering_right_to_left(locale) ? "rtl"sv : "ltr"sv;
+    return Unicode::is_locale_character_ordering_right_to_left(locale.utf16_view()) ? Utf16View { "rtl"sv } : Utf16View { "ltr"sv };
 }
 
 struct FirstDayStringAndValue {
-    StringView weekday;
-    StringView string;
+    Utf16View weekday;
+    Utf16View string;
     u8 value { 0 };
 };
 
 // Table 26: Weekday String and Value, https://tc39.es/ecma402/#table-locale-weekday-string-value
 static constexpr auto WEEKDAY_STRING_AND_VALUE = to_array<FirstDayStringAndValue>({
-    { "0"sv, "sun"sv, 7 },
-    { "1"sv, "mon"sv, 1 },
-    { "2"sv, "tue"sv, 2 },
-    { "3"sv, "wed"sv, 3 },
-    { "4"sv, "thu"sv, 4 },
-    { "5"sv, "fri"sv, 5 },
-    { "6"sv, "sat"sv, 6 },
-    { "7"sv, "sun"sv, 7 },
+    { u"0"sv, u"sun"sv, 7 },
+    { u"1"sv, u"mon"sv, 1 },
+    { u"2"sv, u"tue"sv, 2 },
+    { u"3"sv, u"wed"sv, 3 },
+    { u"4"sv, u"thu"sv, 4 },
+    { u"5"sv, u"fri"sv, 5 },
+    { u"6"sv, u"sat"sv, 6 },
+    { u"7"sv, u"sun"sv, 7 },
 });
 
 // 15.5.15 WeekdayToUValue ( fw ), https://tc39.es/ecma402/#sec-weekdaytouvalue
-StringView weekday_to_u_value(StringView weekday)
+Utf16View weekday_to_u_value(Utf16View weekday)
 {
     // 1. For each row of Table 26, except the header row, in table order, do
     for (auto const& row : WEEKDAY_STRING_AND_VALUE) {
@@ -256,7 +256,7 @@ StringView weekday_to_u_value(StringView weekday)
 }
 
 // 15.5.16 WeekdayUValueToNumber ( fw ), https://tc39.es/ecma402/#sec-weekdayuvaluetonumber
-Optional<u8> weekday_u_value_to_number(StringView weekday)
+Optional<u8> weekday_u_value_to_number(Utf16View weekday)
 {
     // 1. For each row of Table 26, except the header row, in table order, do
     for (auto const& row : WEEKDAY_STRING_AND_VALUE) {
@@ -313,7 +313,7 @@ WeekInfo week_info_of_locale(Locale const& locale_object)
     auto const& locale = locale_object.locale();
 
     // 2. Let r be a Record whose fields are defined by Table 27, with values based on locale.
-    auto locale_week_info = Unicode::week_info_of_locale(locale);
+    auto locale_week_info = Unicode::week_info_of_locale(locale.utf16_view());
 
     WeekInfo week_info {};
     week_info.first_day = weekday_to_integer(locale_week_info.first_day_of_week, Unicode::Weekday::Monday);
@@ -326,7 +326,7 @@ WeekInfo week_info_of_locale(Locale const& locale_object)
         auto const& first_day_of_week_string = locale_object.first_day_of_week();
 
         // 4. Let fw be WeekdayUValueToNumber(fws).
-        first_day_of_week = weekday_u_value_to_number(first_day_of_week_string);
+        first_day_of_week = weekday_u_value_to_number(first_day_of_week_string.utf16_view());
     }
 
     // 5. If fw is not undefined, then
diff --git a/Libraries/LibJS/Runtime/Intl/Locale.h b/Libraries/LibJS/Runtime/Intl/Locale.h
index d1ae7b0679..b0106e75f1 100644
--- a/Libraries/LibJS/Runtime/Intl/Locale.h
+++ b/Libraries/LibJS/Runtime/Intl/Locale.h
@@ -9,6 +9,7 @@
 #include <AK/Array.h>
 #include <AK/Optional.h>
 #include <AK/String.h>
+#include <AK/Utf16String.h>
 #include <AK/Vector.h>
 #include <LibGC/Ptr.h>
 #include <LibJS/Runtime/Completion.h>
@@ -23,7 +24,7 @@ class Locale final : public Object {
     GC_DECLARE_ALLOCATOR(Locale);
 
 public:
-    static GC::Ref<Locale> create(Realm&, GC::Ref<Locale> source_locale, String);
+    static GC::Ref<Locale> create(Realm&, GC::Ref<Locale> source_locale, Utf16String);
 
     static constexpr auto locale_extension_keys()
     {
@@ -31,39 +32,39 @@ public:
         // The value of the [[LocaleExtensionKeys]] internal slot is a List that must include all elements of
         // « "ca", "co", "fw", "hc", "nu" », must additionally include any element of « "kf", "kn" » that is also an
         // element of %Intl.Collator%.[[RelevantExtensionKeys]], and must not include any other elements.
-        return AK::Array { "ca"sv, "co"sv, "fw"sv, "hc"sv, "kf"sv, "kn"sv, "nu"sv };
+        return AK::Array<Utf16View, 7> { "ca"sv, "co"sv, "fw"sv, "hc"sv, "kf"sv, "kn"sv, "nu"sv };
     }
 
     virtual ~Locale() override = default;
 
     Unicode::LocaleID const& locale_id() const;
 
-    String const& locale() const { return m_locale; }
-    void set_locale(String locale) { m_locale = move(locale); }
+    Utf16String const& locale() const { return m_locale; }
+    void set_locale(Utf16String locale) { m_locale = move(locale); }
 
     bool has_calendar() const { return m_calendar.has_value(); }
-    String const& calendar() const { return m_calendar.value(); }
-    void set_calendar(String calendar) { m_calendar = move(calendar); }
+    Utf16String const& calendar() const { return m_calendar.value(); }
+    void set_calendar(Utf16String calendar) { m_calendar = move(calendar); }
 
     bool has_case_first() const { return m_case_first.has_value(); }
-    String const& case_first() const { return m_case_first.value(); }
-    void set_case_first(String case_first) { m_case_first = move(case_first); }
+    Utf16String const& case_first() const { return m_case_first.value(); }
+    void set_case_first(Utf16String case_first) { m_case_first = move(case_first); }
 
     bool has_collation() const { return m_collation.has_value(); }
-    String const& collation() const { return m_collation.value(); }
-    void set_collation(String collation) { m_collation = move(collation); }
+    Utf16String const& collation() const { return m_collation.value(); }
+    void set_collation(Utf16String collation) { m_collation = move(collation); }
 
     bool has_first_day_of_week() const { return m_first_day_of_week.has_value(); }
-    String const& first_day_of_week() const { return m_first_day_of_week.value(); }
-    void set_first_day_of_week(String first_day_of_week) { m_first_day_of_week = move(first_day_of_week); }
+    Utf16String const& first_day_of_week() const { return m_first_day_of_week.value(); }
+    void set_first_day_of_week(Utf16String first_day_of_week) { m_first_day_of_week = move(first_day_of_week); }
 
     bool has_hour_cycle() const { return m_hour_cycle.has_value(); }
-    String const& hour_cycle() const { return m_hour_cycle.value(); }
-    void set_hour_cycle(String hour_cycle) { m_hour_cycle = move(hour_cycle); }
+    Utf16String const& hour_cycle() const { return m_hour_cycle.value(); }
+    void set_hour_cycle(Utf16String hour_cycle) { m_hour_cycle = move(hour_cycle); }
 
     bool has_numbering_system() const { return m_numbering_system.has_value(); }
-    String const& numbering_system() const { return m_numbering_system.value(); }
-    void set_numbering_system(String numbering_system) { m_numbering_system = move(numbering_system); }
+    Utf16String const& numbering_system() const { return m_numbering_system.value(); }
+    void set_numbering_system(Utf16String numbering_system) { m_numbering_system = move(numbering_system); }
 
     bool numeric() const { return m_numeric; }
     void set_numeric(bool numeric) { m_numeric = numeric; }
@@ -71,14 +72,14 @@ public:
 private:
     explicit Locale(Object& prototype);
 
-    String m_locale;                      // [[Locale]]
-    Optional<String> m_calendar;          // [[Calendar]]
-    Optional<String> m_case_first;        // [[CaseFirst]]
-    Optional<String> m_collation;         // [[Collation]]
-    Optional<String> m_first_day_of_week; // [[FirstDayOfWeek]]
-    Optional<String> m_hour_cycle;        // [[HourCycle]]
-    Optional<String> m_numbering_system;  // [[NumberingSystem]]
-    bool m_numeric { false };             // [[Numeric]]
+    Utf16String m_locale;                      // [[Locale]]
+    Optional<Utf16String> m_calendar;          // [[Calendar]]
+    Optional<Utf16String> m_case_first;        // [[CaseFirst]]
+    Optional<Utf16String> m_collation;         // [[Collation]]
+    Optional<Utf16String> m_first_day_of_week; // [[FirstDayOfWeek]]
+    Optional<Utf16String> m_hour_cycle;        // [[HourCycle]]
+    Optional<Utf16String> m_numbering_system;  // [[NumberingSystem]]
+    bool m_numeric { false };                  // [[Numeric]]
 
     mutable Optional<Unicode::LocaleID> m_cached_locale_id;
 };
@@ -89,16 +90,16 @@ struct WeekInfo {
     Vector<u8> weekend; // [[Weekend]]
 };
 
-Optional<String> get_locale_variants(Unicode::LocaleID const&);
+Optional<Utf16String> get_locale_variants(Unicode::LocaleID const&);
 
 GC::Ref<Array> calendars_of_locale(VM&, Locale const&);
 GC::Ref<Array> collations_of_locale(VM&, Locale const& locale);
 GC::Ref<Array> hour_cycles_of_locale(VM&, Locale const& locale);
 GC::Ref<Array> numbering_systems_of_locale(VM&, Locale const&);
 Value time_zones_of_locale(VM&, Locale const&);
-StringView text_direction_of_locale(Locale const&);
-StringView weekday_to_u_value(StringView weekday);
-Optional<u8> weekday_u_value_to_number(StringView weekday);
+Utf16View text_direction_of_locale(Locale const&);
+Utf16View weekday_to_u_value(Utf16View weekday);
+Optional<u8> weekday_u_value_to_number(Utf16View weekday);
 WeekInfo week_info_of_locale(Locale const&);
 
 }
diff --git a/Libraries/LibJS/Runtime/Intl/LocaleConstructor.cpp b/Libraries/LibJS/Runtime/Intl/LocaleConstructor.cpp
index d52f4405b2..82dac60149 100644
--- a/Libraries/LibJS/Runtime/Intl/LocaleConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Intl/LocaleConstructor.cpp
@@ -18,14 +18,24 @@ namespace JS::Intl {
 GC_DEFINE_ALLOCATOR(LocaleConstructor);
 
 struct LocaleAndKeys {
-    String locale;
-    Optional<String> ca;
-    Optional<String> co;
-    Optional<String> fw;
-    Optional<String> hc;
-    Optional<String> kf;
-    Optional<String> kn;
-    Optional<String> nu;
+    Utf16String locale;
+    Optional<Utf16String> ca;
+    Optional<Utf16String> co;
+    Optional<Utf16String> fw;
+    Optional<Utf16String> hc;
+    Optional<Utf16String> kf;
+    Optional<Utf16String> kn;
+    Optional<Utf16String> nu;
+};
+
+struct LocaleOptionsAndKeys {
+    Optional<Utf16String> ca;
+    Optional<Utf16String> co;
+    Optional<Utf16String> fw;
+    Optional<Utf16String> hc;
+    Optional<Utf16String> kf;
+    Optional<Utf16String> kn;
+    Optional<Utf16String> nu;
 };
 
 static bool is_unicode_language_subtag(Utf16View subtag)
@@ -49,26 +59,24 @@ static bool is_type_identifier(Utf16View identifier)
 }
 
 // NOTE: This is not an AO in the spec. This just serves to abstract very similar steps in UpdateLanguageId and the Intl.Locale constructor.
-static ThrowCompletionOr<Optional<String>> get_string_option(VM& vm, Object const& options, PropertyKey const& property, Function<bool(Utf16View)> validator, ReadonlySpan<StringView> values = {}, Optional<String> const& fallback = {})
+static ThrowCompletionOr<Optional<Utf16String>> get_string_option(VM& vm, Object const& options, PropertyKey const& property, Function<bool(Utf16View)> validator, ReadonlySpan<StringView> values = {}, Optional<Utf16String> const& fallback = {})
 {
-    auto option_default = fallback.has_value() ? OptionDefault { *fallback } : Empty {};
-
-    auto option = TRY(get_option(vm, options, property, OptionType::String, values, option_default));
+    auto option = TRY(get_option(vm, options, property, OptionType::String, values, Empty {}));
     if (option.is_undefined())
-        return OptionalNone {};
+        return fallback;
 
-    auto option_string = option.as_string().utf16_string_view();
-    if (!option_string.is_ascii())
+    auto option_string_view = option.as_string().utf16_string_view();
+    if (!option_string_view.has_ascii_storage())
         return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, option, property);
 
-    if (validator && !validator(option_string))
+    if (validator && !validator(option_string_view))
         return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, option, property);
 
-    return MUST(option_string.to_utf8());
+    return Utf16String::from_utf16(option_string_view);
 }
 
 // 15.1.2 UpdateLanguageId ( tag, options ), https://tc39.es/ecma402/#sec-updatelanguageid
-static ThrowCompletionOr<String> update_language_id(VM& vm, StringView tag, Object const& options)
+static ThrowCompletionOr<Utf16String> update_language_id(VM& vm, Utf16View tag, Object const& options)
 {
     auto locale_id = Unicode::parse_unicode_locale_id(tag);
     VERIFY(locale_id.has_value());
@@ -92,7 +100,7 @@ static ThrowCompletionOr<String> update_language_id(VM& vm, StringView tag, Obje
 
     // 8. Let variants be ? GetOption(options, "variants", STRING, EMPTY, GetLocaleVariants(baseName)).
     auto variants = TRY(get_string_option(vm, options, vm.names.variants, nullptr, {}, get_locale_variants(*locale_id)));
-    Vector<String> variant_subtags;
+    Vector<Utf16String> variant_subtags;
 
     // 9. If variants is not undefined, then
     if (variants.has_value()) {
@@ -104,9 +112,12 @@ static ThrowCompletionOr<String> update_language_id(VM& vm, StringView tag, Obje
         auto lower_variants = variants->to_ascii_lowercase();
 
         // c. Let variantSubtags be StringSplitToList(lowerVariants, "-").
-        variant_subtags = MUST(lower_variants.split('-', SplitBehavior::KeepEmpty));
+        lower_variants.utf16_view().for_each_split_view('-', SplitBehavior::KeepEmpty, [&](auto variant) {
+            variant_subtags.append(Utf16String::from_utf16(variant));
+            return IterationDecision::Continue;
+        });
 
-        HashTable<String> seen_variants;
+        HashTable<Utf16String> seen_variants;
         bool has_duplicate_variant = false;
 
         // d. For each element variant of variantSubtags, do
@@ -145,16 +156,16 @@ static ThrowCompletionOr<String> update_language_id(VM& vm, StringView tag, Obje
     new_tag.private_use_extensions = move(private_use_extensions);
 
     // 16. Return newTag.
-    return new_tag.to_string();
+    return new_tag.to_utf16_string();
 }
 
 // 15.1.3 MakeLocaleRecord ( tag, options, localeExtensionKeys ), https://tc39.es/ecma402/#sec-makelocalerecord
-static LocaleAndKeys make_locale_record(StringView tag, LocaleAndKeys options, ReadonlySpan<StringView> locale_extension_keys)
+static LocaleAndKeys make_locale_record(Utf16View tag, LocaleOptionsAndKeys options, ReadonlySpan<Utf16View> locale_extension_keys)
 {
     auto locale_id = Unicode::parse_unicode_locale_id(tag);
     VERIFY(locale_id.has_value());
 
-    Vector<String> attributes;
+    Vector<Utf16String> attributes;
     Vector<Unicode::Keyword> keywords;
 
     // 1. If tag contains a substring that is a Unicode locale extension sequence, then
@@ -174,7 +185,25 @@ static LocaleAndKeys make_locale_record(StringView tag, LocaleAndKeys options, R
     //     a. Let attributes be a new empty List.
     //     b. Let keywords be a new empty List.
 
-    auto field_from_key = [](LocaleAndKeys& value, StringView key) -> Optional<String>& {
+    auto option_field_from_key = [](LocaleOptionsAndKeys& value, Utf16View key) -> Optional<Utf16String>& {
+        if (key == "ca"sv)
+            return value.ca;
+        if (key == "co"sv)
+            return value.co;
+        if (key == "fw"sv)
+            return value.fw;
+        if (key == "hc"sv)
+            return value.hc;
+        if (key == "kf"sv)
+            return value.kf;
+        if (key == "kn"sv)
+            return value.kn;
+        if (key == "nu"sv)
+            return value.nu;
+        VERIFY_NOT_REACHED();
+    };
+
+    auto result_field_from_key = [](LocaleAndKeys& value, Utf16View key) -> Optional<Utf16String>& {
         if (key == "ca"sv)
             return value.ca;
         if (key == "co"sv)
@@ -198,10 +227,10 @@ static LocaleAndKeys make_locale_record(StringView tag, LocaleAndKeys options, R
     // 4. For each element key of localeExtensionKeys, do
     for (auto const& key : locale_extension_keys) {
         Unicode::Keyword* entry = nullptr;
-        Optional<String> value;
+        Optional<Utf16String> value;
 
         // a. If keywords contains an element whose [[Key]] is key, then
-        if (auto it = keywords.find_if([&](auto const& k) { return key == k.key; }); it != keywords.end()) {
+        if (auto it = keywords.find_if([&](auto const& k) { return k.key.utf16_view() == key; }); it != keywords.end()) {
             // i. Let entry be the element of keywords whose [[Key]] is key.
             entry = &(*it);
 
@@ -214,12 +243,12 @@ static LocaleAndKeys make_locale_record(StringView tag, LocaleAndKeys options, R
 
         // c. Assert: options has a field [[<key>]].
         // d. Let overrideValue be options.[[<key>]].
-        auto const& override_value = field_from_key(options, key);
+        auto const& override_value = option_field_from_key(options, key);
 
         // e. If overrideValue is not undefined, then
         if (override_value.has_value()) {
             // i. Set value to CanonicalizeUValue(key, overrideValue).
-            value = Unicode::canonicalize_unicode_extension_values(key, *override_value);
+            value = Unicode::canonicalize_unicode_extension_values(key.bytes(), override_value->utf16_view());
 
             // ii. If entry is not empty, then
             if (entry != nullptr) {
@@ -229,17 +258,18 @@ static LocaleAndKeys make_locale_record(StringView tag, LocaleAndKeys options, R
             // iii. Else,
             else {
                 // 1. Append the Record { [[Key]]: key, [[Value]]: value } to keywords.
-                keywords.empend(MUST(String::from_utf8(key)), *value);
+                keywords.empend(Utf16String::from_utf16(key), *value);
             }
         }
 
         // f. Set result.[[<key>]] to value.
-        field_from_key(result, key) = move(value);
+        if (value.has_value())
+            result_field_from_key(result, key) = *value;
     }
 
     // 5. Let locale be the String value that is tag with any Unicode locale extension sequences removed.
     locale_id->remove_extension_type<Unicode::LocaleExtension>();
-    auto locale = locale_id->to_string();
+    auto locale = locale_id->to_utf16_string();
 
     // 6. If attributes is not empty or keywords is not empty, then
     if (!attributes.is_empty() || !keywords.is_empty()) {
@@ -303,7 +333,7 @@ ThrowCompletionOr<GC::Ref<Object>> LocaleConstructor::construct(FunctionObject&
     if (!tag_value.is_string() && !tag_value.is_object())
         return vm.throw_completion<TypeError>(ErrorType::NotAnObjectOrString, "tag"sv);
 
-    String tag;
+    Utf16String tag;
     bool tag_is_canonicalized = false;
 
     // 8. If tag is an Object and tag has an [[InitializedLocale]] internal slot, then
@@ -329,7 +359,7 @@ ThrowCompletionOr<GC::Ref<Object>> LocaleConstructor::construct(FunctionObject&
     auto options = TRY(coerce_options_to_object(vm, options_value));
 
     // 11. If IsWellFormedLanguageTag(tag) is false, throw a RangeError exception.
-    if (!tag_is_canonicalized && !is_well_formed_language_tag(tag))
+    if (!tag_is_canonicalized && !is_well_formed_language_tag(tag.utf16_view()))
         return vm.throw_completion<RangeError>(ErrorType::IntlInvalidLanguageTag, tag);
 
     // 12. NOTE: Because LanguageId canonicalization can alter tag in arbitrary ways according to Alias Rules from
@@ -337,14 +367,15 @@ ThrowCompletionOr<GC::Ref<Object>> LocaleConstructor::construct(FunctionObject&
     //     options.
 
     // 13. Set tag to CanonicalizeUnicodeLocaleId(tag).
-    if (!tag_is_canonicalized)
-        tag = canonicalize_unicode_locale_id(tag);
+    if (!tag_is_canonicalized) {
+        tag = canonicalize_unicode_locale_id(tag.utf16_view());
+    }
 
     // 14. Set tag to ? UpdateLanguageId(tag, options).
-    tag = TRY(update_language_id(vm, tag, options));
+    tag = TRY(update_language_id(vm, tag.utf16_view(), options));
 
     // 15. Let opt be a new Record.
-    LocaleAndKeys opt {};
+    LocaleOptionsAndKeys opt {};
 
     // 16. Let calendar be ? GetOption(options, "calendar", STRING, EMPTY, undefined).
     // 17. If calendar is not undefined, then
@@ -364,10 +395,10 @@ ThrowCompletionOr<GC::Ref<Object>> LocaleConstructor::construct(FunctionObject&
     // 23. If fw is not undefined, then
     if (first_day_of_week.has_value()) {
         // a. Set fw to WeekdayToUValue(fw).
-        first_day_of_week = MUST(String::from_utf8(weekday_to_u_value(*first_day_of_week)));
+        first_day_of_week = Utf16String::from_utf16(weekday_to_u_value(first_day_of_week->utf16_view()));
 
         // b. If fw cannot be matched by the type Unicode locale nonterminal, throw a RangeError exception.
-        if (!Unicode::is_type_identifier(*first_day_of_week))
+        if (!Unicode::is_type_identifier(first_day_of_week->utf16_view()))
             return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, *first_day_of_week, vm.names.firstDayOfWeek);
     }
 
@@ -388,7 +419,7 @@ ThrowCompletionOr<GC::Ref<Object>> LocaleConstructor::construct(FunctionObject&
     // 30. If kn is not undefined, set kn to ! ToString(kn).
     // 31. Set opt.[[kn]] to kn.
     if (!kn.is_undefined())
-        opt.kn = kn.as_bool() ? "true"_string : "false"_string;
+        opt.kn = kn.as_bool() ? "true"_utf16 : "false"_utf16;
 
     // 32. Let numberingSystem be ? GetOption(options, "numberingSystem", STRING, EMPTY, undefined).
     // 33. If numberingSystem is not undefined, then
@@ -397,7 +428,7 @@ ThrowCompletionOr<GC::Ref<Object>> LocaleConstructor::construct(FunctionObject&
     opt.nu = TRY(get_string_option(vm, options, vm.names.numberingSystem, is_type_identifier));
 
     // 35. Let r be MakeLocaleRecord(tag, opt, localeExtensionKeys).
-    auto result = make_locale_record(tag, move(opt), locale_extension_keys);
+    auto result = make_locale_record(tag.utf16_view(), move(opt), locale_extension_keys);
 
     // 36. Set locale.[[Locale]] to r.[[locale]].
     locale->set_locale(move(result.locale));
@@ -419,16 +450,16 @@ ThrowCompletionOr<GC::Ref<Object>> LocaleConstructor::construct(FunctionObject&
         locale->set_hour_cycle(result.hc.release_value());
 
     // 41. If localeExtensionKeys contains "kf", then
-    if (locale_extension_keys.span().contains_slow("kf"sv)) {
+    if (locale_extension_keys.span().contains_slow(Utf16View { "kf"sv })) {
         // a. Set locale.[[CaseFirst]] to r.[[kf]].
         if (result.kf.has_value())
             locale->set_case_first(result.kf.release_value());
     }
 
     // 42. If localeExtensionKeys contains "kn", then
-    if (locale_extension_keys.span().contains_slow("kn"sv)) {
+    if (locale_extension_keys.span().contains_slow(Utf16View { "kn"sv })) {
         // a. If SameValue(r.[[kn]], "true") is true or r.[[kn]] is the empty String, then
-        if (result.kn.has_value() && (result.kn == "true"sv || result.kn->is_empty())) {
+        if (result.kn.has_value() && (result.kn->utf16_view() == "true"sv || result.kn->is_empty())) {
             // i. Set locale.[[Numeric]] to true.
             locale->set_numeric(true);
         }
diff --git a/Libraries/LibJS/Runtime/Intl/LocalePrototype.cpp b/Libraries/LibJS/Runtime/Intl/LocalePrototype.cpp
index fbcad08cd2..fa1e1fe36f 100644
--- a/Libraries/LibJS/Runtime/Intl/LocalePrototype.cpp
+++ b/Libraries/LibJS/Runtime/Intl/LocalePrototype.cpp
@@ -40,7 +40,7 @@ void LocalePrototype::initialize(Realm& realm)
     define_native_function(realm, vm.names.getWeekInfo, get_week_info, 0, attr);
 
     // 15.3.16 Intl.Locale.prototype [ %Symbol.toStringTag% ], https://tc39.es/ecma402/#sec-intl.locale.prototype-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.Locale"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.Locale"_utf16_fly_string), Attribute::Configurable);
 
     define_native_accessor(realm, vm.names.baseName, base_name, {}, Attribute::Configurable);
     define_native_accessor(realm, vm.names.calendar, calendar, {}, Attribute::Configurable);
@@ -64,7 +64,7 @@ JS_DEFINE_NATIVE_FUNCTION(LocalePrototype::base_name)
     auto locale_object = TRY(typed_this_object(vm));
 
     // 3. Return GetLocaleBaseName(loc.[[Locale]]).
-    return PrimitiveString::create(vm, locale_object->locale_id().language_id.to_string());
+    return PrimitiveString::create(vm, locale_object->locale_id().language_id.to_utf16_string());
 }
 
 #define JS_ENUMERATE_LOCALE_KEYWORD_PROPERTIES \
@@ -113,7 +113,9 @@ JS_DEFINE_NATIVE_FUNCTION(LocalePrototype::maximize)
     auto locale_object = TRY(typed_this_object(vm));
 
     // 3. Let maximal be the result of the Add Likely Subtags algorithm applied to loc.[[Locale]]. If an error is signaled, set maximal to loc.[[Locale]].
-    auto maximal = Unicode::add_likely_subtags(locale_object->locale()).value_or(locale_object->locale());
+    auto maximal = locale_object->locale();
+    if (auto maximal_locale = Unicode::add_likely_subtags(locale_object->locale().utf16_view().bytes()); maximal_locale.has_value())
+        maximal = maximal_locale.release_value();
 
     // 4. Return ! Construct(%Intl.Locale%, maximal).
     return Locale::create(realm, locale_object, move(maximal));
@@ -129,7 +131,9 @@ JS_DEFINE_NATIVE_FUNCTION(LocalePrototype::minimize)
     auto locale_object = TRY(typed_this_object(vm));
 
     // 3. Let minimal be the result of the Remove Likely Subtags algorithm applied to loc.[[Locale]]. If an error is signaled, set minimal to loc.[[Locale]].
-    auto minimal = Unicode::remove_likely_subtags(locale_object->locale()).value_or(locale_object->locale());
+    auto minimal = locale_object->locale();
+    if (auto minimal_locale = Unicode::remove_likely_subtags(locale_object->locale().utf16_view().bytes()); minimal_locale.has_value())
+        minimal = minimal_locale.release_value();
 
     // 4. Return ! Construct(%Intl.Locale%, minimal).
     return Locale::create(realm, locale_object, move(minimal));
diff --git a/Libraries/LibJS/Runtime/Intl/MathematicalValue.cpp b/Libraries/LibJS/Runtime/Intl/MathematicalValue.cpp
index 4d0170e0b6..541adf1ccc 100644
--- a/Libraries/LibJS/Runtime/Intl/MathematicalValue.cpp
+++ b/Libraries/LibJS/Runtime/Intl/MathematicalValue.cpp
@@ -8,6 +8,16 @@
 
 namespace JS::Intl {
 
+MathematicalValue::MathematicalValue(Value value)
+{
+    if (value.is_number()) {
+        m_value = value_from_number(value.as_double());
+        return;
+    }
+
+    m_value = MUST(value.as_bigint().big_integer().to_base_utf16(10));
+}
+
 bool MathematicalValue::is_number() const
 {
     return m_value.has<double>();
diff --git a/Libraries/LibJS/Runtime/Intl/MathematicalValue.h b/Libraries/LibJS/Runtime/Intl/MathematicalValue.h
index e687f25224..38972620f8 100644
--- a/Libraries/LibJS/Runtime/Intl/MathematicalValue.h
+++ b/Libraries/LibJS/Runtime/Intl/MathematicalValue.h
@@ -44,12 +44,7 @@ public:
     {
     }
 
-    MathematicalValue(Value value)
-        : m_value(value.is_number()
-                  ? value_from_number(value.as_double())
-                  : ValueType(Utf16String::from_utf8(MUST(value.as_bigint().big_integer().to_base(10)))))
-    {
-    }
+    MathematicalValue(Value);
 
     bool is_number() const;
     double as_number() const;
diff --git a/Libraries/LibJS/Runtime/Intl/NumberFormat.cpp b/Libraries/LibJS/Runtime/Intl/NumberFormat.cpp
index 898c319dbf..b98f966195 100644
--- a/Libraries/LibJS/Runtime/Intl/NumberFormat.cpp
+++ b/Libraries/LibJS/Runtime/Intl/NumberFormat.cpp
@@ -39,10 +39,10 @@ void NumberFormat::visit_edges(Cell::Visitor& visitor)
 }
 
 // 16.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl.numberformat-internal-slots
-ReadonlySpan<StringView> NumberFormat::relevant_extension_keys() const
+ReadonlySpan<Utf16View> NumberFormat::relevant_extension_keys() const
 {
     // The value of the [[RelevantExtensionKeys]] internal slot is « "nu" ».
-    static constexpr AK::Array keys { "nu"sv };
+    static constexpr AK::Array<Utf16View, 1> keys { "nu"sv };
     return keys;
 }
 
@@ -60,15 +60,15 @@ ReadonlySpan<ResolutionOptionDescriptor> NumberFormat::resolution_option_descrip
     return *descriptors;
 }
 
-StringView NumberFormatBase::computed_rounding_priority_string() const
+Utf16String NumberFormatBase::computed_rounding_priority_string() const
 {
     switch (m_computed_rounding_priority) {
     case ComputedRoundingPriority::Auto:
-        return "auto"sv;
+        return "auto"_utf16;
     case ComputedRoundingPriority::MorePrecision:
-        return "morePrecision"sv;
+        return "morePrecision"_utf16;
     case ComputedRoundingPriority::LessPrecision:
-        return "lessPrecision"sv;
+        return "lessPrecision"_utf16;
     default:
         VERIFY_NOT_REACHED();
     }
@@ -79,8 +79,9 @@ Value NumberFormat::use_grouping_to_value(VM& vm) const
     switch (m_use_grouping) {
     case Unicode::Grouping::Always:
     case Unicode::Grouping::Auto:
-    case Unicode::Grouping::Min2:
+    case Unicode::Grouping::Min2: {
         return PrimitiveString::create(vm, Unicode::grouping_to_string(m_use_grouping));
+    }
     case Unicode::Grouping::False:
         return Value(false);
     default:
@@ -140,11 +141,11 @@ Unicode::DisplayOptions NumberFormat::display_options() const
 }
 
 // 16.5.1 CurrencyDigits ( currency ), https://tc39.es/ecma402/#sec-currencydigits
-int currency_digits(StringView currency)
+int currency_digits(Utf16View currency)
 {
     // 1. If the ISO 4217 currency and funds code list contains currency as an alphabetic code, return the minor
     //    unit value corresponding to the currency from the list; otherwise, return 2.
-    if (auto currency_code = Unicode::get_currency_code(currency); currency_code.has_value())
+    if (auto currency_code = Unicode::get_currency_code(currency.bytes()); currency_code.has_value())
         return currency_code->minor_unit.value_or(2);
     return 2;
 }
@@ -186,7 +187,7 @@ GC::Ref<Array> format_numeric_to_parts(VM& vm, NumberFormat const& number_format
         auto object = Object::create(realm, realm.intrinsics().object_prototype());
 
         // b. Perform ! CreateDataPropertyOrThrow(O, "type", part.[[Type]]).
-        MUST(object->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, part.type)));
+        MUST(object->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, move(part.type))));
 
         // c. Perform ! CreateDataPropertyOrThrow(O, "value", part.[[Value]]).
         MUST(object->create_data_property_or_throw(vm.names.value, PrimitiveString::create(vm, move(part.value))));
@@ -210,7 +211,7 @@ ThrowCompletionOr<MathematicalValue> to_intl_mathematical_value(VM& vm, Value va
 
     // 2. If Type(primValue) is BigInt, return the mathematical value of primValue.
     if (primitive_value.is_bigint())
-        return Utf16String::from_utf8(MUST(value.as_bigint().big_integer().to_base(10)));
+        return MUST(value.as_bigint().big_integer().to_base_utf16(10));
 
     // FIXME: The remaining steps are being refactored into a new Runtime Semantic, StringIntlMV.
     //        We short-circuit some of these steps to avoid known pitfalls.
@@ -303,13 +304,13 @@ ThrowCompletionOr<GC::Ref<Array>> format_numeric_range_to_parts(VM& vm, NumberFo
         auto object = Object::create(realm, realm.intrinsics().object_prototype());
 
         // b. Perform ! CreateDataPropertyOrThrow(O, "type", part.[[Type]]).
-        MUST(object->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, part.type)));
+        MUST(object->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, move(part.type))));
 
         // c. Perform ! CreateDataPropertyOrThrow(O, "value", part.[[Value]]).
         MUST(object->create_data_property_or_throw(vm.names.value, PrimitiveString::create(vm, move(part.value))));
 
         // d. Perform ! CreateDataPropertyOrThrow(O, "source", part.[[Source]]).
-        MUST(object->create_data_property_or_throw(vm.names.source, PrimitiveString::create(vm, part.source)));
+        MUST(object->create_data_property_or_throw(vm.names.source, PrimitiveString::create(vm, move(part.source))));
 
         // e. Perform ! CreateDataPropertyOrThrow(result, ! ToString(n), O).
         MUST(result->create_data_property_or_throw(n, object));
diff --git a/Libraries/LibJS/Runtime/Intl/NumberFormat.h b/Libraries/LibJS/Runtime/Intl/NumberFormat.h
index d1743ebe57..6c4995627b 100644
--- a/Libraries/LibJS/Runtime/Intl/NumberFormat.h
+++ b/Libraries/LibJS/Runtime/Intl/NumberFormat.h
@@ -8,6 +8,7 @@
 
 #include <AK/Optional.h>
 #include <AK/String.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 #include <LibJS/Export.h>
 #include <LibJS/Runtime/Intl/AbstractOperations.h>
@@ -32,8 +33,8 @@ public:
 
     virtual ~NumberFormatBase() override = default;
 
-    String const& locale() const { return m_locale; }
-    void set_locale(String locale) { m_locale = move(locale); }
+    Utf16String const& locale() const { return m_locale; }
+    void set_locale(Utf16String locale) { m_locale = move(locale); }
 
     int min_integer_digits() const { return m_min_integer_digits; }
     void set_min_integer_digits(int min_integer_digits) { m_min_integer_digits = min_integer_digits; }
@@ -55,35 +56,31 @@ public:
     void set_max_significant_digits(int max_significant_digits) { m_max_significant_digits = max_significant_digits; }
 
     Unicode::Notation notation() const { return m_notation; }
-    StringView notation_string() const { return Unicode::notation_to_string(m_notation); }
-    void set_notation(StringView notation) { m_notation = Unicode::notation_from_string(notation); }
+    Utf16String notation_string() const { return Unicode::notation_to_string(m_notation); }
     void set_notation(Utf16View notation) { m_notation = Unicode::notation_from_string(notation); }
 
     bool has_compact_display() const { return m_compact_display.has_value(); }
     Unicode::CompactDisplay compact_display() const { return *m_compact_display; }
-    StringView compact_display_string() const { return Unicode::compact_display_to_string(*m_compact_display); }
-    void set_compact_display(StringView compact_display) { m_compact_display = Unicode::compact_display_from_string(compact_display); }
+    Utf16String compact_display_string() const { return Unicode::compact_display_to_string(*m_compact_display); }
     void set_compact_display(Utf16View compact_display) { m_compact_display = Unicode::compact_display_from_string(compact_display); }
 
     Unicode::RoundingType rounding_type() const { return m_rounding_type; }
-    StringView rounding_type_string() const { return Unicode::rounding_type_to_string(m_rounding_type); }
+    Utf16String rounding_type_string() const { return Unicode::rounding_type_to_string(m_rounding_type); }
     void set_rounding_type(Unicode::RoundingType rounding_type) { m_rounding_type = rounding_type; }
 
     ComputedRoundingPriority computed_rounding_priority() const { return m_computed_rounding_priority; }
-    StringView computed_rounding_priority_string() const;
+    Utf16String computed_rounding_priority_string() const;
     void set_computed_rounding_priority(ComputedRoundingPriority computed_rounding_priority) { m_computed_rounding_priority = computed_rounding_priority; }
 
     Unicode::RoundingMode rounding_mode() const { return m_rounding_mode; }
-    StringView rounding_mode_string() const { return Unicode::rounding_mode_to_string(m_rounding_mode); }
-    void set_rounding_mode(StringView rounding_mode) { m_rounding_mode = Unicode::rounding_mode_from_string(rounding_mode); }
+    Utf16String rounding_mode_string() const { return Unicode::rounding_mode_to_string(m_rounding_mode); }
     void set_rounding_mode(Utf16View rounding_mode) { m_rounding_mode = Unicode::rounding_mode_from_string(rounding_mode); }
 
     int rounding_increment() const { return m_rounding_increment; }
     void set_rounding_increment(int rounding_increment) { m_rounding_increment = rounding_increment; }
 
     Unicode::TrailingZeroDisplay trailing_zero_display() const { return m_trailing_zero_display; }
-    StringView trailing_zero_display_string() const { return Unicode::trailing_zero_display_to_string(m_trailing_zero_display); }
-    void set_trailing_zero_display(StringView trailing_zero_display) { m_trailing_zero_display = Unicode::trailing_zero_display_from_string(trailing_zero_display); }
+    Utf16String trailing_zero_display_string() const { return Unicode::trailing_zero_display_to_string(m_trailing_zero_display); }
     void set_trailing_zero_display(Utf16View trailing_zero_display) { m_trailing_zero_display = Unicode::trailing_zero_display_from_string(trailing_zero_display); }
 
     virtual Unicode::DisplayOptions display_options() const;
@@ -96,7 +93,7 @@ protected:
     explicit NumberFormatBase(Object& prototype);
 
 private:
-    String m_locale;                                                                             // [[Locale]]
+    Utf16String m_locale;                                                                        // [[Locale]]
     int m_min_integer_digits { 0 };                                                              // [[MinimumIntegerDigits]]
     Optional<int> m_min_fraction_digits {};                                                      // [[MinimumFractionDigits]]
     Optional<int> m_max_fraction_digits {};                                                      // [[MaximumFractionDigits]]
@@ -121,41 +118,37 @@ class NumberFormat final : public NumberFormatBase {
 public:
     virtual ~NumberFormat() override = default;
 
-    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<Utf16View> relevant_extension_keys() const override;
     virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
 
-    String const& numbering_system() const { return m_numbering_system; }
-    void set_numbering_system(String numbering_system) { m_numbering_system = move(numbering_system); }
+    Utf16String const& numbering_system() const { return m_numbering_system; }
+    void set_numbering_system(Utf16String numbering_system) { m_numbering_system = move(numbering_system); }
 
     Unicode::NumberFormatStyle style() const { return m_style; }
-    StringView style_string() const { return Unicode::number_format_style_to_string(m_style); }
-    void set_style(StringView style) { m_style = Unicode::number_format_style_from_string(style); }
+    Utf16String style_string() const { return Unicode::number_format_style_to_string(m_style); }
     void set_style(Utf16View style) { m_style = Unicode::number_format_style_from_string(style); }
 
     bool has_currency() const { return m_currency.has_value(); }
-    String const& currency() const { return m_currency.value(); }
-    void set_currency(String currency) { m_currency = move(currency); }
+    Utf16String const& currency() const { return m_currency.value(); }
+    void set_currency(Utf16String currency) { m_currency = move(currency); }
 
     bool has_currency_display() const { return m_currency_display.has_value(); }
     Unicode::CurrencyDisplay currency_display() const { return *m_currency_display; }
-    StringView currency_display_string() const { return Unicode::currency_display_to_string(*m_currency_display); }
-    void set_currency_display(StringView currency_display) { m_currency_display = Unicode::currency_display_from_string(currency_display); }
+    Utf16String currency_display_string() const { return Unicode::currency_display_to_string(*m_currency_display); }
     void set_currency_display(Utf16View currency_display) { m_currency_display = Unicode::currency_display_from_string(currency_display); }
 
     bool has_currency_sign() const { return m_currency_sign.has_value(); }
     Unicode::CurrencySign currency_sign() const { return *m_currency_sign; }
-    StringView currency_sign_string() const { return Unicode::currency_sign_to_string(*m_currency_sign); }
-    void set_currency_sign(StringView currency_sign) { m_currency_sign = Unicode::currency_sign_from_string(currency_sign); }
+    Utf16String currency_sign_string() const { return Unicode::currency_sign_to_string(*m_currency_sign); }
     void set_currency_sign(Utf16View currency_sign) { m_currency_sign = Unicode::currency_sign_from_string(currency_sign); }
 
     bool has_unit() const { return m_unit.has_value(); }
-    String const& unit() const { return m_unit.value(); }
-    void set_unit(String unit) { m_unit = move(unit); }
+    Utf16String const& unit() const { return m_unit.value(); }
+    void set_unit(Utf16String unit) { m_unit = move(unit); }
 
     bool has_unit_display() const { return m_unit_display.has_value(); }
     Unicode::Style unit_display() const { return *m_unit_display; }
-    StringView unit_display_string() const { return Unicode::style_to_string(*m_unit_display); }
-    void set_unit_display(StringView unit_display) { m_unit_display = Unicode::style_from_string(unit_display); }
+    Utf16String unit_display_string() const { return Unicode::style_to_string(*m_unit_display); }
     void set_unit_display(Utf16View unit_display) { m_unit_display = Unicode::style_from_string(unit_display); }
 
     Unicode::Grouping use_grouping() const { return m_use_grouping; }
@@ -163,8 +156,7 @@ public:
     void set_use_grouping(StringOrBoolean const& use_grouping);
 
     Unicode::SignDisplay sign_display() const { return m_sign_display; }
-    StringView sign_display_string() const { return Unicode::sign_display_to_string(m_sign_display); }
-    void set_sign_display(StringView sign_display) { m_sign_display = Unicode::sign_display_from_string(sign_display); }
+    Utf16String sign_display_string() const { return Unicode::sign_display_to_string(m_sign_display); }
     void set_sign_display(Utf16View sign_display) { m_sign_display = Unicode::sign_display_from_string(sign_display); }
 
     NativeFunction* bound_format() const { return m_bound_format; }
@@ -177,20 +169,19 @@ private:
 
     virtual void visit_edges(Visitor&) override;
 
-    String m_locale;                                               // [[Locale]]
-    String m_numbering_system;                                     // [[NumberingSystem]]
+    Utf16String m_numbering_system;                                // [[NumberingSystem]]
     Unicode::NumberFormatStyle m_style;                            // [[Style]]
-    Optional<String> m_currency;                                   // [[Currency]]
+    Optional<Utf16String> m_currency;                              // [[Currency]]
     Optional<Unicode::CurrencyDisplay> m_currency_display;         // [[CurrencyDisplay]]
     Optional<Unicode::CurrencySign> m_currency_sign;               // [[CurrencySign]]
-    Optional<String> m_unit;                                       // [[Unit]]
+    Optional<Utf16String> m_unit;                                  // [[Unit]]
     Optional<Unicode::Style> m_unit_display;                       // [[UnitDisplay]]
     Unicode::Grouping m_use_grouping { Unicode::Grouping::False }; // [[UseGrouping]]
     Unicode::SignDisplay m_sign_display;                           // [[SignDisplay]]
     GC::Ptr<NativeFunction> m_bound_format;                        // [[BoundFormat]]
 };
 
-int currency_digits(StringView currency);
+int currency_digits(Utf16View currency);
 Vector<Unicode::NumberFormat::Partition> partition_number_pattern(NumberFormat const&, MathematicalValue const& number);
 Utf16String format_numeric(NumberFormat const&, MathematicalValue const& number);
 GC::Ref<Array> format_numeric_to_parts(VM&, NumberFormat const&, MathematicalValue const& number);
diff --git a/Libraries/LibJS/Runtime/Intl/NumberFormatConstructor.cpp b/Libraries/LibJS/Runtime/Intl/NumberFormatConstructor.cpp
index 28ea596077..6a059b0208 100644
--- a/Libraries/LibJS/Runtime/Intl/NumberFormatConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Intl/NumberFormatConstructor.cpp
@@ -16,7 +16,7 @@ namespace JS::Intl {
 
 GC_DEFINE_ALLOCATOR(NumberFormatConstructor);
 
-static String ascii_uppercase_currency_code(Utf16View currency)
+static Utf16String ascii_uppercase_currency_code(Utf16View currency)
 {
     VERIFY(currency.length_in_code_units() == 3);
 
@@ -26,7 +26,7 @@ static String ascii_uppercase_currency_code(Utf16View currency)
         code[i] = static_cast<char>(to_ascii_uppercase(currency.code_unit_at(i)));
     }
 
-    return String::from_ascii_short_string_without_validation(code, 3);
+    return Utf16String::from_ascii_without_validation({ code, 3 });
 }
 
 // 16.1 The Intl.NumberFormat Constructor, https://tc39.es/ecma402/#sec-intl-numberformat-constructor
@@ -79,7 +79,7 @@ ThrowCompletionOr<GC::Ref<Object>> NumberFormatConstructor::construct(FunctionOb
     // 7. Set numberFormat.[[LocaleData]] to r.[[LocaleData]].
 
     // 8. Set numberFormat.[[NumberingSystem]] to r.[[nu]].
-    if (auto* resolved_numbering_system = result.nu.get_pointer<String>())
+    if (auto* resolved_numbering_system = result.nu.get_pointer<Utf16String>())
         number_format->set_numbering_system(move(*resolved_numbering_system));
 
     // 9. Perform ? SetNumberFormatUnitOptions(numberFormat, options).
@@ -89,7 +89,7 @@ ThrowCompletionOr<GC::Ref<Object>> NumberFormatConstructor::construct(FunctionOb
     auto style = number_format->style();
 
     // 11. Let notation be ? GetOption(options, "notation", STRING, « "standard", "scientific", "engineering", "compact" », "standard").
-    auto notation = TRY(get_option(vm, *options, vm.names.notation, OptionType::String, { "standard"sv, "scientific"sv, "engineering"sv, "compact"sv }, "standard"sv));
+    auto notation = TRY(get_option(vm, *options, vm.names.notation, OptionType::String, { "standard"sv, "scientific"sv, "engineering"sv, "compact"sv }, u"standard"sv));
 
     // 12. Set numberFormat.[[Notation]] to notation.
     number_format->set_notation(notation.as_string().utf16_string_view());
@@ -127,7 +127,7 @@ ThrowCompletionOr<GC::Ref<Object>> NumberFormatConstructor::construct(FunctionOb
     TRY(set_number_format_digit_options(vm, number_format, *options, default_min_fraction_digits, default_max_fraction_digits, number_format->notation()));
 
     // 16. Let compactDisplay be ? GetOption(options, "compactDisplay", STRING, « "short", "long" », "short").
-    auto compact_display = TRY(get_option(vm, *options, vm.names.compactDisplay, OptionType::String, { "short"sv, "long"sv }, "short"sv));
+    auto compact_display = TRY(get_option(vm, *options, vm.names.compactDisplay, OptionType::String, { "short"sv, "long"sv }, u"short"sv));
 
     // 17. Let defaultUseGrouping be "auto".
     auto default_use_grouping = "auto"sv;
@@ -161,7 +161,7 @@ ThrowCompletionOr<GC::Ref<Object>> NumberFormatConstructor::construct(FunctionOb
     number_format->set_use_grouping(use_grouping);
 
     // 24. Let signDisplay be ? GetOption(options, "signDisplay", STRING, « "auto", "never", "always", "exceptZero", "negative" », "auto").
-    auto sign_display = TRY(get_option(vm, *options, vm.names.signDisplay, OptionType::String, { "auto"sv, "never"sv, "always"sv, "exceptZero"sv, "negative"sv }, "auto"sv));
+    auto sign_display = TRY(get_option(vm, *options, vm.names.signDisplay, OptionType::String, { "auto"sv, "never"sv, "always"sv, "exceptZero"sv, "negative"sv }, u"auto"sv));
 
     // 25. Set numberFormat.[[SignDisplay]] to signDisplay.
     number_format->set_sign_display(sign_display.as_string().utf16_string_view());
@@ -172,7 +172,7 @@ ThrowCompletionOr<GC::Ref<Object>> NumberFormatConstructor::construct(FunctionOb
 
     // Non-standard, create an ICU number formatter for this Intl object.
     auto formatter = Unicode::NumberFormat::create(
-        result.icu_locale,
+        result.icu_locale.utf16_view().bytes(),
         number_format->display_options(),
         number_format->rounding_options());
     number_format->set_formatter(move(formatter));
@@ -212,14 +212,14 @@ ThrowCompletionOr<void> set_number_format_digit_options(VM& vm, NumberFormatBase
         return vm.throw_completion<RangeError>(ErrorType::IntlInvalidRoundingIncrement, *rounding_increment);
 
     // 9. Let roundingMode be ? GetOption(options, "roundingMode", STRING, « "ceil", "floor", "expand", "trunc", "halfCeil", "halfFloor", "halfExpand", "halfTrunc", "halfEven" », "halfExpand").
-    auto rounding_mode = TRY(get_option(vm, options, vm.names.roundingMode, OptionType::String, { "ceil"sv, "floor"sv, "expand"sv, "trunc"sv, "halfCeil"sv, "halfFloor"sv, "halfExpand"sv, "halfTrunc"sv, "halfEven"sv }, "halfExpand"sv));
+    auto rounding_mode = TRY(get_option(vm, options, vm.names.roundingMode, OptionType::String, { "ceil"sv, "floor"sv, "expand"sv, "trunc"sv, "halfCeil"sv, "halfFloor"sv, "halfExpand"sv, "halfTrunc"sv, "halfEven"sv }, u"halfExpand"sv));
 
     // 10. Let roundingPriority be ? GetOption(options, "roundingPriority", STRING, « "auto", "morePrecision", "lessPrecision" », "auto").
-    auto rounding_priority_option = TRY(get_option(vm, options, vm.names.roundingPriority, OptionType::String, { "auto"sv, "morePrecision"sv, "lessPrecision"sv }, "auto"sv));
+    auto rounding_priority_option = TRY(get_option(vm, options, vm.names.roundingPriority, OptionType::String, { "auto"sv, "morePrecision"sv, "lessPrecision"sv }, u"auto"sv));
     auto rounding_priority = rounding_priority_option.as_string().utf16_string_view();
 
     // 11. Let trailingZeroDisplay be ? GetOption(options, "trailingZeroDisplay", STRING, « "auto", "stripIfInteger" », "auto").
-    auto trailing_zero_display = TRY(get_option(vm, options, vm.names.trailingZeroDisplay, OptionType::String, { "auto"sv, "stripIfInteger"sv }, "auto"sv));
+    auto trailing_zero_display = TRY(get_option(vm, options, vm.names.trailingZeroDisplay, OptionType::String, { "auto"sv, "stripIfInteger"sv }, u"auto"sv));
 
     // 12. NOTE: All fields required by SetNumberFormatDigitOptions have now been read from options. The remainder of this AO interprets the options and may throw exceptions.
 
@@ -390,7 +390,7 @@ ThrowCompletionOr<void> set_number_format_digit_options(VM& vm, NumberFormatBase
 ThrowCompletionOr<void> set_number_format_unit_options(VM& vm, NumberFormat& intl_object, Object const& options)
 {
     // 1. Let style be ? GetOption(options, "style", STRING, « "decimal", "percent", "currency", "unit" », "decimal").
-    auto style = TRY(get_option(vm, options, vm.names.style, OptionType::String, { "decimal"sv, "percent"sv, "currency"sv, "unit"sv }, "decimal"sv));
+    auto style = TRY(get_option(vm, options, vm.names.style, OptionType::String, { "decimal"sv, "percent"sv, "currency"sv, "unit"sv }, u"decimal"sv));
 
     // 2. Set intlObj.[[Style]] to style.
     intl_object.set_style(style.as_string().utf16_string_view());
@@ -411,10 +411,10 @@ ThrowCompletionOr<void> set_number_format_unit_options(VM& vm, NumberFormat& int
     }
 
     // 6. Let currencyDisplay be ? GetOption(options, "currencyDisplay", STRING, « "code", "symbol", "narrowSymbol", "name" », "symbol").
-    auto currency_display = TRY(get_option(vm, options, vm.names.currencyDisplay, OptionType::String, { "code"sv, "symbol"sv, "narrowSymbol"sv, "name"sv }, "symbol"sv));
+    auto currency_display = TRY(get_option(vm, options, vm.names.currencyDisplay, OptionType::String, { "code"sv, "symbol"sv, "narrowSymbol"sv, "name"sv }, u"symbol"sv));
 
     // 7. Let currencySign be ? GetOption(options, "currencySign", STRING, « "standard", "accounting" », "standard").
-    auto currency_sign = TRY(get_option(vm, options, vm.names.currencySign, OptionType::String, { "standard"sv, "accounting"sv }, "standard"sv));
+    auto currency_sign = TRY(get_option(vm, options, vm.names.currencySign, OptionType::String, { "standard"sv, "accounting"sv }, u"standard"sv));
 
     // 8. Let unit be ? GetOption(options, "unit", STRING, EMPTY, undefined).
     auto unit = TRY(get_option(vm, options, vm.names.unit, OptionType::String, {}, Empty {}));
@@ -432,7 +432,7 @@ ThrowCompletionOr<void> set_number_format_unit_options(VM& vm, NumberFormat& int
     }
 
     // 11. Let unitDisplay be ? GetOption(options, "unitDisplay", STRING, « "short", "narrow", "long" », "short").
-    auto unit_display = TRY(get_option(vm, options, vm.names.unitDisplay, OptionType::String, { "short"sv, "narrow"sv, "long"sv }, "short"sv));
+    auto unit_display = TRY(get_option(vm, options, vm.names.unitDisplay, OptionType::String, { "short"sv, "narrow"sv, "long"sv }, u"short"sv));
 
     // 12. If style is "currency", then
     if (intl_object.style() == Unicode::NumberFormatStyle::Currency) {
@@ -449,7 +449,7 @@ ThrowCompletionOr<void> set_number_format_unit_options(VM& vm, NumberFormat& int
     // 13. If style is "unit", then
     if (intl_object.style() == Unicode::NumberFormatStyle::Unit) {
         // a. Set intlObj.[[Unit]] to unit.
-        intl_object.set_unit(MUST(unit.as_string().utf16_string_view().to_utf8()));
+        intl_object.set_unit(unit.as_string().utf16_string());
 
         // b. Set intlObj.[[UnitDisplay]] to unitDisplay.
         intl_object.set_unit_display(unit_display.as_string().utf16_string_view());
diff --git a/Libraries/LibJS/Runtime/Intl/NumberFormatFunction.cpp b/Libraries/LibJS/Runtime/Intl/NumberFormatFunction.cpp
index 6634597f49..5cea077b85 100644
--- a/Libraries/LibJS/Runtime/Intl/NumberFormatFunction.cpp
+++ b/Libraries/LibJS/Runtime/Intl/NumberFormatFunction.cpp
@@ -30,7 +30,7 @@ void NumberFormatFunction::initialize(Realm& realm)
 
     Base::initialize(realm);
     define_direct_property(vm.names.length, Value(1), Attribute::Configurable);
-    define_direct_property(vm.names.name, PrimitiveString::create(vm, String {}), Attribute::Configurable);
+    define_direct_property(vm.names.name, PrimitiveString::create(vm, Utf16String {}), Attribute::Configurable);
 }
 
 ThrowCompletionOr<Value> NumberFormatFunction::call()
diff --git a/Libraries/LibJS/Runtime/Intl/NumberFormatPrototype.cpp b/Libraries/LibJS/Runtime/Intl/NumberFormatPrototype.cpp
index c503fd200d..96b5a1f3b8 100644
--- a/Libraries/LibJS/Runtime/Intl/NumberFormatPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Intl/NumberFormatPrototype.cpp
@@ -28,7 +28,7 @@ void NumberFormatPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 16.3.7 Intl.NumberFormat.prototype [ %Symbol.toStringTag% ], https://tc39.es/ecma402/#sec-intl.numberformat.prototype-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.NumberFormat"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.NumberFormat"_utf16_fly_string), Attribute::Configurable);
 
     define_native_accessor(realm, vm.names.format, format, nullptr, Attribute::Configurable);
 
diff --git a/Libraries/LibJS/Runtime/Intl/PluralRules.cpp b/Libraries/LibJS/Runtime/Intl/PluralRules.cpp
index ad603d4165..813199e390 100644
--- a/Libraries/LibJS/Runtime/Intl/PluralRules.cpp
+++ b/Libraries/LibJS/Runtime/Intl/PluralRules.cpp
@@ -18,7 +18,7 @@ PluralRules::PluralRules(Object& prototype)
 }
 
 // 17.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl.pluralrules-internal-slots
-ReadonlySpan<StringView> PluralRules::relevant_extension_keys() const
+ReadonlySpan<Utf16View> PluralRules::relevant_extension_keys() const
 {
     // The value of the [[RelevantExtensionKeys]] internal slot is « ».
     return {};
diff --git a/Libraries/LibJS/Runtime/Intl/PluralRules.h b/Libraries/LibJS/Runtime/Intl/PluralRules.h
index 8ae1d885b4..bd2a0c8bef 100644
--- a/Libraries/LibJS/Runtime/Intl/PluralRules.h
+++ b/Libraries/LibJS/Runtime/Intl/PluralRules.h
@@ -7,6 +7,7 @@
 #pragma once
 
 #include <AK/StringView.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/Intl/NumberFormat.h>
@@ -22,12 +23,11 @@ class PluralRules final : public NumberFormatBase {
 public:
     virtual ~PluralRules() override = default;
 
-    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<Utf16View> relevant_extension_keys() const override;
     virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
 
     Unicode::PluralForm type() const { return m_type; }
-    StringView type_string() const { return Unicode::plural_form_to_string(m_type); }
-    void set_type(StringView type) { m_type = Unicode::plural_form_from_string(type); }
+    Utf16String type_string() const { return Unicode::plural_form_to_string(m_type); }
     void set_type(Utf16View type) { m_type = Unicode::plural_form_from_string(type); }
 
 private:
diff --git a/Libraries/LibJS/Runtime/Intl/PluralRulesConstructor.cpp b/Libraries/LibJS/Runtime/Intl/PluralRulesConstructor.cpp
index 4389e549a5..0f7c19823d 100644
--- a/Libraries/LibJS/Runtime/Intl/PluralRulesConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Intl/PluralRulesConstructor.cpp
@@ -64,19 +64,19 @@ ThrowCompletionOr<GC::Ref<Object>> PluralRulesConstructor::construct(FunctionObj
     plural_rules->set_locale(move(result.locale));
 
     // 7. Let t be ? GetOption(options, "type", string, « "cardinal", "ordinal" », "cardinal").
-    auto type = TRY(get_option(vm, *options, vm.names.type, OptionType::String, AK::Array { "cardinal"sv, "ordinal"sv }, "cardinal"sv));
+    auto type = TRY(get_option(vm, *options, vm.names.type, OptionType::String, AK::Array { "cardinal"sv, "ordinal"sv }, u"cardinal"sv));
 
     // 8. Set pluralRules.[[Type]] to t.
     plural_rules->set_type(type.as_string().utf16_string_view());
 
     // 9. Let notation be ? GetOption(options, "notation", string, « "standard", "scientific", "engineering", "compact" », "standard").
-    auto notation = TRY(get_option(vm, *options, vm.names.notation, OptionType::String, { "standard"sv, "scientific"sv, "engineering"sv, "compact"sv }, "standard"sv));
+    auto notation = TRY(get_option(vm, *options, vm.names.notation, OptionType::String, { "standard"sv, "scientific"sv, "engineering"sv, "compact"sv }, u"standard"sv));
 
     // 10. Set pluralRules.[[Notation]] to notation.
     plural_rules->set_notation(notation.as_string().utf16_string_view());
 
     // 11. Let compactDisplay be ? GetOption(options, "compactDisplay", string, « "short", "long" », "short").
-    auto compact_display = TRY(get_option(vm, *options, vm.names.compactDisplay, OptionType::String, { "short"sv, "long"sv }, "short"sv));
+    auto compact_display = TRY(get_option(vm, *options, vm.names.compactDisplay, OptionType::String, { "short"sv, "long"sv }, u"short"sv));
 
     // 12. If notation is "compact", then
     if (plural_rules->notation() == Unicode::Notation::Compact) {
@@ -89,7 +89,7 @@ ThrowCompletionOr<GC::Ref<Object>> PluralRulesConstructor::construct(FunctionObj
 
     // Non-standard, create an ICU number formatter for this Intl object.
     auto formatter = Unicode::NumberFormat::create(
-        result.icu_locale,
+        result.icu_locale.utf16_view().bytes(),
         plural_rules->display_options(),
         plural_rules->rounding_options());
 
diff --git a/Libraries/LibJS/Runtime/Intl/PluralRulesPrototype.cpp b/Libraries/LibJS/Runtime/Intl/PluralRulesPrototype.cpp
index 2ea4cb4a0e..0558a4310a 100644
--- a/Libraries/LibJS/Runtime/Intl/PluralRulesPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Intl/PluralRulesPrototype.cpp
@@ -28,7 +28,7 @@ void PluralRulesPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 17.3.5 Intl.PluralRules.prototype [ %Symbol.toStringTag% ], https://tc39.es/ecma402/#sec-intl.pluralrules.prototype-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.PluralRules"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.PluralRules"_utf16_fly_string), Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(realm, vm.names.resolvedOptions, resolved_options, 0, attr);
diff --git a/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.cpp b/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.cpp
index 80ce3e3299..c79e05cd8f 100644
--- a/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.cpp
+++ b/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.cpp
@@ -21,10 +21,10 @@ RelativeTimeFormat::RelativeTimeFormat(Object& prototype)
 }
 
 // 18.2.3 Internal slots, https://tc39.es/ecma402/#sec-Intl.RelativeTimeFormat-internal-slots
-ReadonlySpan<StringView> RelativeTimeFormat::relevant_extension_keys() const
+ReadonlySpan<Utf16View> RelativeTimeFormat::relevant_extension_keys() const
 {
     // The value of the [[RelevantExtensionKeys]] internal slot is « "nu" ».
-    static constexpr AK::Array keys { "nu"sv };
+    static constexpr AK::Array<Utf16View, 1> keys { "nu"sv };
     return keys;
 }
 
@@ -131,7 +131,7 @@ ThrowCompletionOr<GC::Ref<Array>> format_relative_time_to_parts(VM& vm, Relative
         auto object = Object::create(realm, realm.intrinsics().object_prototype());
 
         // b. Perform ! CreateDataPropertyOrThrow(O, "type", part.[[Type]]).
-        MUST(object->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, part.type)));
+        MUST(object->create_data_property_or_throw(vm.names.type, PrimitiveString::create(vm, move(part.type))));
 
         // c. Perform ! CreateDataPropertyOrThrow(O, "value", part.[[Value]]).
         MUST(object->create_data_property_or_throw(vm.names.value, PrimitiveString::create(vm, move(part.value))));
@@ -139,7 +139,7 @@ ThrowCompletionOr<GC::Ref<Array>> format_relative_time_to_parts(VM& vm, Relative
         // d. If part.[[Unit]] is not empty, then
         if (!part.unit.is_empty()) {
             // i. Perform ! CreateDataPropertyOrThrow(O, "unit", part.[[Unit]]).
-            MUST(object->create_data_property_or_throw(vm.names.unit, PrimitiveString::create(vm, part.unit)));
+            MUST(object->create_data_property_or_throw(vm.names.unit, PrimitiveString::create(vm, move(part.unit))));
         }
 
         // e. Perform ! CreateDataPropertyOrThrow(result, ! ToString(n), O).
diff --git a/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.h b/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.h
index eb7f713f82..a261302f33 100644
--- a/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.h
+++ b/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.h
@@ -6,8 +6,8 @@
 
 #pragma once
 
-#include <AK/String.h>
 #include <AK/StringView.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/Intl/IntlObject.h>
@@ -23,24 +23,22 @@ class RelativeTimeFormat final : public IntlObject {
 public:
     virtual ~RelativeTimeFormat() override = default;
 
-    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<Utf16View> relevant_extension_keys() const override;
     virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
 
-    String const& locale() const { return m_locale; }
-    void set_locale(String locale) { m_locale = move(locale); }
+    Utf16String const& locale() const { return m_locale; }
+    void set_locale(Utf16String locale) { m_locale = move(locale); }
 
-    String const& numbering_system() const { return m_numbering_system; }
-    void set_numbering_system(String numbering_system) { m_numbering_system = move(numbering_system); }
+    Utf16String const& numbering_system() const { return m_numbering_system; }
+    void set_numbering_system(Utf16String numbering_system) { m_numbering_system = move(numbering_system); }
 
     Unicode::Style style() const { return m_style; }
-    void set_style(StringView style) { m_style = Unicode::style_from_string(style); }
     void set_style(Utf16View style) { m_style = Unicode::style_from_string(style); }
-    StringView style_string() const { return Unicode::style_to_string(m_style); }
+    Utf16String style_string() const { return Unicode::style_to_string(m_style); }
 
     Unicode::NumericDisplay numeric() const { return m_numeric; }
-    void set_numeric(StringView numeric) { m_numeric = Unicode::numeric_display_from_string(numeric); }
     void set_numeric(Utf16View numeric) { m_numeric = Unicode::numeric_display_from_string(numeric); }
-    StringView numeric_string() const { return Unicode::numeric_display_to_string(m_numeric); }
+    Utf16String numeric_string() const { return Unicode::numeric_display_to_string(m_numeric); }
 
     Unicode::RelativeTimeFormat const& formatter() const { return *m_formatter; }
     void set_formatter(NonnullOwnPtr<Unicode::RelativeTimeFormat> formatter) { m_formatter = move(formatter); }
@@ -48,8 +46,8 @@ public:
 private:
     explicit RelativeTimeFormat(Object& prototype);
 
-    String m_locale;                                                       // [[Locale]]
-    String m_numbering_system;                                             // [[NumberingSystem]]
+    Utf16String m_locale;                                                  // [[Locale]]
+    Utf16String m_numbering_system;                                        // [[NumberingSystem]]
     Unicode::Style m_style { Unicode::Style::Long };                       // [[Style]]
     Unicode::NumericDisplay m_numeric { Unicode::NumericDisplay::Always }; // [[Numeric]]
 
diff --git a/Libraries/LibJS/Runtime/Intl/RelativeTimeFormatConstructor.cpp b/Libraries/LibJS/Runtime/Intl/RelativeTimeFormatConstructor.cpp
index 576e0fe791..aea69d1603 100644
--- a/Libraries/LibJS/Runtime/Intl/RelativeTimeFormatConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Intl/RelativeTimeFormatConstructor.cpp
@@ -60,7 +60,7 @@ ThrowCompletionOr<GC::Ref<Object>> RelativeTimeFormatConstructor::construct(Func
     auto [options, result, _] = TRY(resolve_options(vm, relative_time_format, locales_value, options_value, SpecialBehaviors::CoerceOptions));
 
     // 6. Let locale be r.[[Locale]].
-    auto locale = move(result.locale);
+    auto locale = result.locale;
 
     // 7. Set relativeTimeFormat.[[Locale]] to locale.
     relative_time_format->set_locale(locale);
@@ -68,17 +68,17 @@ ThrowCompletionOr<GC::Ref<Object>> RelativeTimeFormatConstructor::construct(Func
     // 8. Set relativeTimeFormat.[[LocaleData]] to r.[[LocaleData]].
 
     // 9. Set relativeTimeFormat.[[NumberingSystem]] to r.[[nu]].
-    if (auto* resolved_numbering_system = result.nu.get_pointer<String>())
+    if (auto* resolved_numbering_system = result.nu.get_pointer<Utf16String>())
         relative_time_format->set_numbering_system(move(*resolved_numbering_system));
 
     // 10. Let style be ? GetOption(options, "style", STRING, « "long", "short", "narrow" », "long").
-    auto style = TRY(get_option(vm, *options, vm.names.style, OptionType::String, { "long"sv, "short"sv, "narrow"sv }, "long"sv));
+    auto style = TRY(get_option(vm, *options, vm.names.style, OptionType::String, { "long"sv, "short"sv, "narrow"sv }, u"long"sv));
 
     // 11. Set relativeTimeFormat.[[Style]] to style.
     relative_time_format->set_style(style.as_string().utf16_string_view());
 
     // 12. Let numeric be ? GetOption(options, "numeric", STRING, « "always", "auto" », "always").
-    auto numeric = TRY(get_option(vm, *options, vm.names.numeric, OptionType::String, { "always"sv, "auto"sv }, "always"sv));
+    auto numeric = TRY(get_option(vm, *options, vm.names.numeric, OptionType::String, { "always"sv, "auto"sv }, u"always"sv));
 
     // 13. Set relativeTimeFormat.[[Numeric]] to numeric.
     relative_time_format->set_numeric(numeric.as_string().utf16_string_view());
@@ -88,7 +88,7 @@ ThrowCompletionOr<GC::Ref<Object>> RelativeTimeFormatConstructor::construct(Func
     // 16. Let relativeTimeFormat.[[NumberFormat]] be ! Construct(%Intl.NumberFormat%, « locale, nfOptions »).
     // 17. Let relativeTimeFormat.[[PluralRules]] be ! Construct(%Intl.PluralRules%, « locale »).
     auto formatter = Unicode::RelativeTimeFormat::create(
-        result.icu_locale,
+        result.icu_locale.utf16_view().bytes(),
         relative_time_format->style());
     relative_time_format->set_formatter(move(formatter));
 
diff --git a/Libraries/LibJS/Runtime/Intl/RelativeTimeFormatPrototype.cpp b/Libraries/LibJS/Runtime/Intl/RelativeTimeFormatPrototype.cpp
index 7c9a6671ae..813055a3dc 100644
--- a/Libraries/LibJS/Runtime/Intl/RelativeTimeFormatPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Intl/RelativeTimeFormatPrototype.cpp
@@ -26,7 +26,7 @@ void RelativeTimeFormatPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 18.3.5 Intl.RelativeTimeFormat.prototype [ %Symbol.toStringTag% ], https://tc39.es/ecma402/#sec-Intl.RelativeTimeFormat.prototype-toStringTag
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.RelativeTimeFormat"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.RelativeTimeFormat"_utf16_fly_string), Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(realm, vm.names.resolvedOptions, resolved_options, 0, attr);
diff --git a/Libraries/LibJS/Runtime/Intl/SegmentIteratorPrototype.cpp b/Libraries/LibJS/Runtime/Intl/SegmentIteratorPrototype.cpp
index 40aa749e52..5dad97030b 100644
--- a/Libraries/LibJS/Runtime/Intl/SegmentIteratorPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Intl/SegmentIteratorPrototype.cpp
@@ -27,7 +27,7 @@ void SegmentIteratorPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 19.6.2.2 %IntlSegmentIteratorPrototype% [ %Symbol.toStringTag% ], https://tc39.es/ecma402/#sec-%intlsegmentiteratorprototype%.%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Segmenter String Iterator"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Segmenter String Iterator"_utf16_fly_string), Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(realm, vm.names.next, next, 0, attr);
diff --git a/Libraries/LibJS/Runtime/Intl/Segmenter.cpp b/Libraries/LibJS/Runtime/Intl/Segmenter.cpp
index 436cc529e3..43339aa711 100644
--- a/Libraries/LibJS/Runtime/Intl/Segmenter.cpp
+++ b/Libraries/LibJS/Runtime/Intl/Segmenter.cpp
@@ -20,7 +20,7 @@ Segmenter::Segmenter(Object& prototype)
 }
 
 // 19.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl.segmenter-internal-slots
-ReadonlySpan<StringView> Segmenter::relevant_extension_keys() const
+ReadonlySpan<Utf16View> Segmenter::relevant_extension_keys() const
 {
     // The value of the [[RelevantExtensionKeys]] internal slot is « ».
     return {};
diff --git a/Libraries/LibJS/Runtime/Intl/Segmenter.h b/Libraries/LibJS/Runtime/Intl/Segmenter.h
index 5b6da25cc4..c894c14bb1 100644
--- a/Libraries/LibJS/Runtime/Intl/Segmenter.h
+++ b/Libraries/LibJS/Runtime/Intl/Segmenter.h
@@ -7,7 +7,7 @@
 
 #pragma once
 
-#include <AK/String.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 #include <LibJS/Runtime/Intl/IntlObject.h>
 #include <LibUnicode/Segmenter.h>
@@ -21,16 +21,15 @@ class Segmenter final : public IntlObject {
 public:
     virtual ~Segmenter() override = default;
 
-    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<Utf16View> relevant_extension_keys() const override;
     virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
 
-    String const& locale() const { return m_locale; }
-    void set_locale(String locale) { m_locale = move(locale); }
+    Utf16String const& locale() const { return m_locale; }
+    void set_locale(Utf16String locale) { m_locale = move(locale); }
 
     Unicode::SegmenterGranularity segmenter_granularity() const { return m_segmenter_granularity; }
-    void set_segmenter_granularity(StringView segmenter_granularity) { m_segmenter_granularity = Unicode::segmenter_granularity_from_string(segmenter_granularity); }
     void set_segmenter_granularity(Utf16View segmenter_granularity) { m_segmenter_granularity = Unicode::segmenter_granularity_from_string(segmenter_granularity); }
-    StringView segmenter_granularity_string() const { return Unicode::segmenter_granularity_to_string(m_segmenter_granularity); }
+    Utf16String segmenter_granularity_string() const { return Unicode::segmenter_granularity_to_string(m_segmenter_granularity); }
 
     Unicode::Segmenter const& segmenter() const { return *m_segmenter; }
     void set_segmenter(NonnullOwnPtr<Unicode::Segmenter> segmenter) { m_segmenter = move(segmenter); }
@@ -38,7 +37,7 @@ public:
 private:
     explicit Segmenter(Object& prototype);
 
-    String m_locale;                                                                                   // [[Locale]]
+    Utf16String m_locale;                                                                              // [[Locale]]
     Unicode::SegmenterGranularity m_segmenter_granularity { Unicode::SegmenterGranularity::Grapheme }; // [[SegmenterGranularity]]
 
     // Non-standard. Stores the ICU segmenter for the Intl object's segmentation options.
diff --git a/Libraries/LibJS/Runtime/Intl/SegmenterConstructor.cpp b/Libraries/LibJS/Runtime/Intl/SegmenterConstructor.cpp
index c48feb2fec..f416607803 100644
--- a/Libraries/LibJS/Runtime/Intl/SegmenterConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Intl/SegmenterConstructor.cpp
@@ -64,12 +64,12 @@ ThrowCompletionOr<GC::Ref<Object>> SegmenterConstructor::construct(FunctionObjec
     segmenter->set_locale(move(result.locale));
 
     // 8. Let granularity be ? GetOption(options, "granularity", string, « "grapheme", "word", "sentence" », "grapheme").
-    auto granularity = TRY(get_option(vm, *options, vm.names.granularity, OptionType::String, { "grapheme"sv, "word"sv, "sentence"sv }, "grapheme"sv));
+    auto granularity = TRY(get_option(vm, *options, vm.names.granularity, OptionType::String, { "grapheme"sv, "word"sv, "sentence"sv }, u"grapheme"sv));
 
     // 9. Set segmenter.[[SegmenterGranularity]] to granularity.
     segmenter->set_segmenter_granularity(granularity.as_string().utf16_string_view());
 
-    auto locale_segmenter = Unicode::Segmenter::create(segmenter->locale(), segmenter->segmenter_granularity());
+    auto locale_segmenter = Unicode::Segmenter::create(result.icu_locale.utf16_view().bytes(), segmenter->segmenter_granularity());
     segmenter->set_segmenter(move(locale_segmenter));
 
     // 10. Return segmenter.
diff --git a/Libraries/LibJS/Runtime/Intl/SegmenterPrototype.cpp b/Libraries/LibJS/Runtime/Intl/SegmenterPrototype.cpp
index 4271187afc..1393e62a5b 100644
--- a/Libraries/LibJS/Runtime/Intl/SegmenterPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Intl/SegmenterPrototype.cpp
@@ -26,7 +26,7 @@ void SegmenterPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 19.3.4 Intl.Segmenter.prototype [ %Symbol.toStringTag% ], https://tc39.es/ecma402/#sec-intl.segmenter.prototype-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.Segmenter"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Intl.Segmenter"_utf16_fly_string), Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(realm, vm.names.resolvedOptions, resolved_options, 0, attr);
diff --git a/Libraries/LibJS/Runtime/Intl/SingleUnitIdentifiers.h b/Libraries/LibJS/Runtime/Intl/SingleUnitIdentifiers.h
index dbed1e11ac..217568afdb 100644
--- a/Libraries/LibJS/Runtime/Intl/SingleUnitIdentifiers.h
+++ b/Libraries/LibJS/Runtime/Intl/SingleUnitIdentifiers.h
@@ -7,7 +7,7 @@
 #pragma once
 
 #include <AK/Array.h>
-#include <AK/StringView.h>
+#include <AK/Utf16View.h>
 
 namespace JS::Intl {
 
@@ -15,51 +15,51 @@ namespace JS::Intl {
 constexpr auto sanctioned_single_unit_identifiers()
 {
     return AK::Array {
-        "acre"sv,
-        "bit"sv,
-        "byte"sv,
-        "celsius"sv,
-        "centimeter"sv,
-        "day"sv,
-        "degree"sv,
-        "fahrenheit"sv,
-        "fluid-ounce"sv,
-        "foot"sv,
-        "gallon"sv,
-        "gigabit"sv,
-        "gigabyte"sv,
-        "gram"sv,
-        "hectare"sv,
-        "hour"sv,
-        "inch"sv,
-        "kilobit"sv,
-        "kilobyte"sv,
-        "kilogram"sv,
-        "kilometer"sv,
-        "liter"sv,
-        "megabit"sv,
-        "megabyte"sv,
-        "meter"sv,
-        "microsecond"sv,
-        "mile"sv,
-        "mile-scandinavian"sv,
-        "milliliter"sv,
-        "millimeter"sv,
-        "millisecond"sv,
-        "minute"sv,
-        "month"sv,
-        "nanosecond"sv,
-        "ounce"sv,
-        "percent"sv,
-        "petabyte"sv,
-        "pound"sv,
-        "second"sv,
-        "stone"sv,
-        "terabit"sv,
-        "terabyte"sv,
-        "week"sv,
-        "yard"sv,
-        "year"sv,
+        u"acre"sv,
+        u"bit"sv,
+        u"byte"sv,
+        u"celsius"sv,
+        u"centimeter"sv,
+        u"day"sv,
+        u"degree"sv,
+        u"fahrenheit"sv,
+        u"fluid-ounce"sv,
+        u"foot"sv,
+        u"gallon"sv,
+        u"gigabit"sv,
+        u"gigabyte"sv,
+        u"gram"sv,
+        u"hectare"sv,
+        u"hour"sv,
+        u"inch"sv,
+        u"kilobit"sv,
+        u"kilobyte"sv,
+        u"kilogram"sv,
+        u"kilometer"sv,
+        u"liter"sv,
+        u"megabit"sv,
+        u"megabyte"sv,
+        u"meter"sv,
+        u"microsecond"sv,
+        u"mile"sv,
+        u"mile-scandinavian"sv,
+        u"milliliter"sv,
+        u"millimeter"sv,
+        u"millisecond"sv,
+        u"minute"sv,
+        u"month"sv,
+        u"nanosecond"sv,
+        u"ounce"sv,
+        u"percent"sv,
+        u"petabyte"sv,
+        u"pound"sv,
+        u"second"sv,
+        u"stone"sv,
+        u"terabit"sv,
+        u"terabyte"sv,
+        u"week"sv,
+        u"yard"sv,
+        u"year"sv,
     };
 }
 
diff --git a/Libraries/LibJS/Runtime/Intrinsics.cpp b/Libraries/LibJS/Runtime/Intrinsics.cpp
index 309885a608..e4d4b5736d 100644
--- a/Libraries/LibJS/Runtime/Intrinsics.cpp
+++ b/Libraries/LibJS/Runtime/Intrinsics.cpp
@@ -323,7 +323,7 @@ void Intrinsics::initialize_intrinsics(Realm& realm)
         },
         0, Utf16FlyString {}, &realm);
     m_throw_type_error_function->define_direct_property(vm.names.length, Value(0), 0);
-    m_throw_type_error_function->define_direct_property(vm.names.name, PrimitiveString::create(vm, String {}), 0);
+    m_throw_type_error_function->define_direct_property(vm.names.name, PrimitiveString::create(vm, Utf16String {}), 0);
     MUST(m_throw_type_error_function->internal_prevent_extensions());
 
     m_throw_type_error_accessor = Accessor::create(
diff --git a/Libraries/LibJS/Runtime/IteratorHelperPrototype.cpp b/Libraries/LibJS/Runtime/IteratorHelperPrototype.cpp
index 361691a548..03fd667b14 100644
--- a/Libraries/LibJS/Runtime/IteratorHelperPrototype.cpp
+++ b/Libraries/LibJS/Runtime/IteratorHelperPrototype.cpp
@@ -28,7 +28,7 @@ void IteratorHelperPrototype::initialize(Realm& realm)
     define_native_function(realm, vm.names.return_, return_, 0, attr);
 
     // 27.1.2.1.3 %IteratorHelperPrototype% [ %Symbol.toStringTag% ], https://tc39.es/ecma262/#sec-%iteratorhelperprototype%-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Iterator Helper"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Iterator Helper"_utf16_fly_string), Attribute::Configurable);
 }
 
 // 27.1.2.1.1 %IteratorHelperPrototype%.next ( ), https://tc39.es/ecma262/#sec-%iteratorhelperprototype%.next
diff --git a/Libraries/LibJS/Runtime/JSONObject.cpp b/Libraries/LibJS/Runtime/JSONObject.cpp
index 3d5d98df63..fe20e423ac 100644
--- a/Libraries/LibJS/Runtime/JSONObject.cpp
+++ b/Libraries/LibJS/Runtime/JSONObject.cpp
@@ -46,7 +46,7 @@ void JSONObject::initialize(Realm& realm)
     define_native_function(realm, vm.names.isRawJSON, is_raw_json, 1, attr);
 
     // 25.5.3 JSON [ @@toStringTag ], https://tc39.es/ecma262/#sec-json-@@tostringtag
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "JSON"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "JSON"_utf16_fly_string), Attribute::Configurable);
 }
 
 // 25.5.2 JSON.stringify ( value [ , replacer [ , space ] ] ), https://tc39.es/ecma262/#sec-json.stringify
@@ -604,10 +604,10 @@ static ALWAYS_INLINE ThrowCompletionOr<void> ensure_simdjson_fully_parsed(VM& vm
 static ThrowCompletionOr<Value> parse_simdjson_value(VM&, simdjson::ondemand::value, JSONParseRecord* record = nullptr);
 
 // The source text matched by a primitive parse node, used by JSON.parse revivers.
-static String json_token_source(std::string_view raw)
+static Utf16String json_token_source(std::string_view raw)
 {
     StringView source { raw.data(), raw.size() };
-    return MUST(String::from_utf8(source.trim_whitespace()));
+    return Utf16String::from_utf8(source.trim_whitespace());
 }
 
 template<typename T>
diff --git a/Libraries/LibJS/Runtime/JSONObject.h b/Libraries/LibJS/Runtime/JSONObject.h
index 801e8e2701..7c6362e772 100644
--- a/Libraries/LibJS/Runtime/JSONObject.h
+++ b/Libraries/LibJS/Runtime/JSONObject.h
@@ -7,6 +7,8 @@
 #pragma once
 
 #include <AK/Utf16StringBuilder.h>
+#include <AK/Utf16String.h>
+#include <AK/Utf16View.h>
 #include <LibJS/Export.h>
 #include <LibJS/Runtime/Object.h>
 
@@ -22,7 +24,7 @@ struct JSONParseRecord {
     // NB: In place of the spec's [[ParseNode]] field, we capture the source text
     //     matched by the parse node up front. It is present only when [[Value]] is
     //     a primitive, since the reviver context only exposes "source" for those.
-    Optional<String> source;
+    Optional<Utf16String> source;
     // [[Elements]]: if [[Value]] is an Array, the records for its elements; else empty.
     Vector<JSONParseRecord> elements;
     // [[Entries]]: if [[Value]] is a non-Array Object, the records for its entries; else empty.
diff --git a/Libraries/LibJS/Runtime/MapConstructor.cpp b/Libraries/LibJS/Runtime/MapConstructor.cpp
index 0f8f9eb590..4a51f89bcb 100644
--- a/Libraries/LibJS/Runtime/MapConstructor.cpp
+++ b/Libraries/LibJS/Runtime/MapConstructor.cpp
@@ -60,7 +60,7 @@ ThrowCompletionOr<GC::Ref<Object>> MapConstructor::construct(FunctionObject& new
 
     (void)TRY(get_iterator_values(vm, vm.argument(0), [&](Value iterator_value) -> Optional<Completion> {
         if (!iterator_value.is_object())
-            return vm.throw_completion<TypeError>(ErrorType::NotAnObject, ByteString::formatted("Iterator value {}", iterator_value));
+            return vm.throw_completion<TypeError>(ErrorType::NotAnObject, Utf16String::formatted("Iterator value {}", iterator_value));
 
         auto key = TRY(iterator_value.as_object().get(0));
         auto value = TRY(iterator_value.as_object().get(1));
diff --git a/Libraries/LibJS/Runtime/MapIteratorPrototype.cpp b/Libraries/LibJS/Runtime/MapIteratorPrototype.cpp
index f1dfb4d6db..4ca79b4f25 100644
--- a/Libraries/LibJS/Runtime/MapIteratorPrototype.cpp
+++ b/Libraries/LibJS/Runtime/MapIteratorPrototype.cpp
@@ -24,7 +24,7 @@ void MapIteratorPrototype::initialize(Realm& realm)
     Base::initialize(realm);
 
     define_native_function(realm, vm.names.next, next, 0, Attribute::Configurable | Attribute::Writable, Bytecode::Builtin::MapIteratorPrototypeNext);
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Map Iterator"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Map Iterator"_utf16_fly_string), Attribute::Configurable);
 }
 
 // 24.1.5.2.1 %MapIteratorPrototype%.next ( ), https://tc39.es/ecma262/#sec-%mapiteratorprototype%.next
diff --git a/Libraries/LibJS/Runtime/ModuleNamespaceObject.cpp b/Libraries/LibJS/Runtime/ModuleNamespaceObject.cpp
index 80a22de8c1..c6dc983e5d 100644
--- a/Libraries/LibJS/Runtime/ModuleNamespaceObject.cpp
+++ b/Libraries/LibJS/Runtime/ModuleNamespaceObject.cpp
@@ -30,7 +30,7 @@ void ModuleNamespaceObject::initialize(Realm& realm)
     Base::initialize(realm);
 
     // 28.3.1 @@toStringTag, https://tc39.es/ecma262/#sec-@@tostringtag
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Module"_string), 0);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Module"_utf16_fly_string), 0);
 }
 
 size_t ModuleNamespaceObject::external_memory_size() const
diff --git a/Libraries/LibJS/Runtime/NumberPrototype.cpp b/Libraries/LibJS/Runtime/NumberPrototype.cpp
index 355004852b..9a498485bf 100644
--- a/Libraries/LibJS/Runtime/NumberPrototype.cpp
+++ b/Libraries/LibJS/Runtime/NumberPrototype.cpp
@@ -10,8 +10,10 @@
 #include <AK/FloatingPoint.h>
 #include <AK/Function.h>
 #include <AK/NeverDestroyed.h>
+#include <AK/StringBuilder.h>
 #include <AK/StringConversions.h>
 #include <AK/TypeCasts.h>
+#include <AK/Utf16StringBuilder.h>
 #include <LibCrypto/BigInt/UnsignedBigInteger.h>
 #include <LibJS/Runtime/AbstractOperations.h>
 #include <LibJS/Runtime/Completion.h>
@@ -288,7 +290,7 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_exponential)
     // 7. Let s be the empty String.
     auto sign = ""sv;
 
-    String number_string;
+    Utf16String number_string;
     int exponent = 0;
 
     // 8. If x < 0, then
@@ -303,7 +305,7 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_exponential)
     // 9. If x = 0, then
     if (number == 0) {
         // a. Let m be the String value consisting of f + 1 occurrences of the code unit 0x0030 (DIGIT ZERO).
-        number_string = MUST(String::repeated('0', fraction_digits + 1));
+        number_string = Utf16String::repeated('0', fraction_digits + 1);
 
         // b. Let e be 0.
         exponent = 0;
@@ -335,23 +337,23 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_exponential)
         }
 
         // c. Let m be the String value consisting of the digits of the decimal representation of n (in order, with no leading zeroes).
-        number_string = MUST(significand.to_base(10));
+        number_string = MUST(significand.to_base_utf16(10));
     }
 
     // 11. If f ≠ 0, then
     if (fraction_digits != 0) {
         // a. Let a be the first code unit of m.
-        auto first = number_string.bytes_as_string_view().substring_view(0, 1);
+        auto first = number_string.substring_view(0, 1);
 
         // b. Let b be the other f code units of m.
-        auto second = number_string.bytes_as_string_view().substring_view(1);
+        auto second = number_string.substring_view(1);
 
         // c. Set m to the string-concatenation of a, ".", and b.
-        number_string = MUST(String::formatted("{}.{}", first, second));
+        number_string = Utf16String::formatted("{}.{}", first, second);
     }
 
     char exponent_sign = 0;
-    String exponent_string;
+    Utf16String exponent_string;
 
     // 12. If e = 0, then
     if (exponent == 0) {
@@ -359,7 +361,7 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_exponential)
         exponent_sign = '+';
 
         // b. Let d be "0".
-        exponent_string = "0"_string;
+        exponent_string = "0"_utf16;
     }
     // 13. Else,
     else {
@@ -380,12 +382,12 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_exponential)
         }
 
         // c. Let d be the String value consisting of the digits of the decimal representation of e (in order, with no leading zeroes).
-        exponent_string = String::number(exponent);
+        exponent_string = Utf16String::number(exponent);
     }
 
     // 14. Set m to the string-concatenation of m, "e", c, and d.
     // 15. Return the string-concatenation of s and m.
-    return PrimitiveString::create(vm, MUST(String::formatted("{}{}e{}{}", sign, number_string, exponent_sign, exponent_string)));
+    return PrimitiveString::create(vm, Utf16String::formatted("{}{}e{}{}", sign, number_string, exponent_sign, exponent_string));
 }
 
 // 21.1.3.3 Number.prototype.toFixed ( fractionDigits ), https://tc39.es/ecma262/#sec-number.prototype.tofixed
@@ -441,23 +443,23 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_fixed)
     // 12. Return the string-concatenation of s and m.
 
     auto fraction_digit_count = static_cast<u32>(fraction_digits);
-    auto number_string = MUST(compute_to_fixed_scaled_integer(number, fraction_digit_count).to_base(10));
+    auto number_string = MUST(compute_to_fixed_scaled_integer(number, fraction_digit_count).to_base_utf16(10));
 
     if (fraction_digit_count != 0) {
-        auto k = number_string.bytes_as_string_view().length();
+        auto k = number_string.length_in_code_units();
         if (k <= fraction_digit_count) {
-            auto zeroes = MUST(String::repeated('0', fraction_digit_count + 1 - k));
-            number_string = MUST(String::formatted("{}{}", zeroes, number_string));
+            auto zeroes = Utf16String::repeated('0', fraction_digit_count + 1 - k);
+            number_string = Utf16String::formatted("{}{}", zeroes, number_string);
             k = fraction_digit_count + 1;
         }
 
-        auto number_string_view = number_string.bytes_as_string_view();
+        auto number_string_view = number_string.utf16_view();
         auto whole_part = number_string_view.substring_view(0, k - fraction_digit_count);
         auto fractional_part = number_string_view.substring_view(k - fraction_digit_count);
-        number_string = MUST(String::formatted("{}.{}", whole_part, fractional_part));
+        number_string = Utf16String::formatted("{}.{}", whole_part, fractional_part);
     }
 
-    return PrimitiveString::create(vm, MUST(String::formatted("{}{}", s, number_string)));
+    return PrimitiveString::create(vm, Utf16String::formatted("{}{}", s, number_string));
 }
 
 // 20.2.1 Number.prototype.toLocaleString ( [ locales [ , options ] ] ), https://tc39.es/ecma402/#sup-number.prototype.tolocalestring
@@ -508,7 +510,7 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_precision)
     // 7. Let s be the empty String.
     auto sign = ""sv;
 
-    String number_string;
+    Utf16String number_string;
     int exponent = 0;
 
     // 8. If x < 0, then
@@ -523,7 +525,7 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_precision)
     // 9. If x = 0, then
     if (number == 0) {
         // a. Let m be the String value consisting of p occurrences of the code unit 0x0030 (DIGIT ZERO).
-        number_string = MUST(String::repeated('0', precision));
+        number_string = Utf16String::repeated('0', precision);
 
         // b. Let e be 0.
         exponent = 0;
@@ -537,7 +539,7 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_precision)
 
         // b. Let m be the String value consisting of the digits of the decimal representation of n (in order, with no
         //    leading zeroes).
-        number_string = MUST(result.significand.to_base(10));
+        number_string = MUST(result.significand.to_base_utf16(10));
 
         // c. If e < -6 or e ≥ p, then
         if ((exponent < -6) || (exponent >= precision)) {
@@ -547,13 +549,13 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_precision)
             // ii. If p ≠ 1, then
             if (precision != 1) {
                 // 1. Let a be the first code unit of m.
-                auto first = number_string.bytes_as_string_view().substring_view(0, 1);
+                auto first = number_string.substring_view(0, 1);
 
                 // 2. Let b be the other p - 1 code units of m.
-                auto second = number_string.bytes_as_string_view().substring_view(1);
+                auto second = number_string.substring_view(1);
 
                 // 3. Set m to the string-concatenation of a, ".", and b.
-                number_string = MUST(String::formatted("{}.{}", first, second));
+                number_string = Utf16String::formatted("{}.{}", first, second);
             }
 
             char exponent_sign = 0;
@@ -576,36 +578,37 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_precision)
             }
 
             // v. Let d be the String value consisting of the digits of the decimal representation of e (in order, with no leading zeroes).
-            auto exponent_string = String::number(exponent);
+            auto exponent_string = Utf16String::number(exponent);
 
             // vi. Return the string-concatenation of s, m, the code unit 0x0065 (LATIN SMALL LETTER E), c, and d.
-            return PrimitiveString::create(vm, MUST(String::formatted("{}{}e{}{}", sign, number_string, exponent_sign, exponent_string)));
+            return PrimitiveString::create(vm, Utf16String::formatted("{}{}e{}{}", sign, number_string, exponent_sign, exponent_string));
         }
     }
 
     // 11. If e = p - 1, return the string-concatenation of s and m.
-    if (exponent == precision - 1)
-        return PrimitiveString::create(vm, MUST(String::formatted("{}{}", sign, number_string)));
+    if (exponent == precision - 1) {
+        return PrimitiveString::create(vm, Utf16String::formatted("{}{}", sign, number_string));
+    }
 
     // 12. If e ≥ 0, then
     if (exponent >= 0) {
         // a. Set m to the string-concatenation of the first e + 1 code units of m, the code unit 0x002E (FULL STOP), and the remaining p - (e + 1) code units of m.
-        number_string = MUST(String::formatted(
+        number_string = Utf16String::formatted(
             "{}.{}",
-            number_string.bytes_as_string_view().substring_view(0, exponent + 1),
-            number_string.bytes_as_string_view().substring_view(exponent + 1)));
+            number_string.substring_view(0, exponent + 1),
+            number_string.substring_view(exponent + 1));
     }
     // 13. Else,
     else {
         // a. Set m to the string-concatenation of the code unit 0x0030 (DIGIT ZERO), the code unit 0x002E (FULL STOP), -(e + 1) occurrences of the code unit 0x0030 (DIGIT ZERO), and the String m.
-        number_string = MUST(String::formatted(
+        number_string = Utf16String::formatted(
             "0.{}{}",
-            MUST(String::repeated('0', -1 * (exponent + 1))),
-            number_string));
+            Utf16String::repeated('0', -1 * (exponent + 1)),
+            number_string);
     }
 
     // 14. Return the string-concatenation of s and m.
-    return PrimitiveString::create(vm, MUST(String::formatted("{}{}", sign, number_string)));
+    return PrimitiveString::create(vm, Utf16String::formatted("{}{}", sign, number_string));
 }
 
 // 21.1.3.6 Number.prototype.toString ( [ radix ] ), https://tc39.es/ecma262/#sec-number.prototype.tostring
@@ -633,13 +636,13 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_string)
 
     // 6. Return the String representation of this Number value using the radix specified by radixMV. Letters a-z are used for digits with values 10 through 35. The precise algorithm is implementation-defined, however the algorithm should be a generalization of that specified in 6.1.6.1.20.
     if (number_value.is_positive_infinity())
-        return PrimitiveString::create(vm, "Infinity"_string);
+        return PrimitiveString::create(vm, "Infinity"_utf16_fly_string);
     if (number_value.is_negative_infinity())
-        return PrimitiveString::create(vm, "-Infinity"_string);
+        return PrimitiveString::create(vm, "-Infinity"_utf16_fly_string);
     if (number_value.is_nan())
-        return PrimitiveString::create(vm, "NaN"_string);
+        return PrimitiveString::create(vm, "NaN"_utf16_fly_string);
     if (number_value.is_positive_zero() || number_value.is_negative_zero())
-        return PrimitiveString::create(vm, "0"_string);
+        return PrimitiveString::create(vm, "0"_utf16_fly_string);
 
     double number = number_value.as_double();
     bool negative = number < 0;
@@ -662,33 +665,37 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_string)
         }
     }
 
-    Vector<char> characters;
+    Utf16StringBuilder builder;
     if (negative)
-        characters.append('-');
+        builder.append_ascii('-');
 
     // Reverse characters;
     for (ssize_t i = backwards_characters.size() - 1; i >= 0; --i) {
-        characters.append(backwards_characters[i]);
+        builder.append_code_unit(backwards_characters[i]);
     }
 
     // decimal part
     if (decimal_part != 0.0) {
-        characters.append('.');
+        builder.append_ascii('.');
 
         u8 precision = max_precision_for_radix[radix];
 
         for (u8 i = 0; i < precision; ++i) {
             decimal_part *= radix;
             u64 integral = floor(decimal_part);
-            characters.append(digits[integral]);
+            builder.append_code_unit(digits[integral]);
             decimal_part -= integral;
         }
 
-        while (characters.last() == '0')
-            characters.take_last();
+        for (;;) {
+            auto view = builder.view();
+            if (view.code_unit_at(view.length_in_code_units() - 1) != '0')
+                break;
+            builder.trim(1);
+        }
     }
 
-    return PrimitiveString::create(vm, String::from_utf8_without_validation(ReadonlyBytes { characters.data(), characters.size() }));
+    return PrimitiveString::create(vm, builder.to_string());
 }
 
 // 21.1.3.7 Number.prototype.valueOf ( ), https://tc39.es/ecma262/#sec-number.prototype.valueof
diff --git a/Libraries/LibJS/Runtime/ObjectConstructor.cpp b/Libraries/LibJS/Runtime/ObjectConstructor.cpp
index db6b29baab..fd03497005 100644
--- a/Libraries/LibJS/Runtime/ObjectConstructor.cpp
+++ b/Libraries/LibJS/Runtime/ObjectConstructor.cpp
@@ -279,7 +279,7 @@ JS_DEFINE_NATIVE_FUNCTION(ObjectConstructor::from_entries)
     // 6. Return ? AddEntriesFromIterable(obj, iterable, adder).
     (void)TRY(get_iterator_values(vm, iterable, [&](Value iterator_value) -> Optional<Completion> {
         if (!iterator_value.is_object())
-            return vm.throw_completion<TypeError>(ErrorType::NotAnObject, ByteString::formatted("Iterator value {}", iterator_value));
+            return vm.throw_completion<TypeError>(ErrorType::NotAnObject, Utf16String::formatted("Iterator value {}", iterator_value));
 
         auto key = TRY(iterator_value.as_object().get(0));
         auto value = TRY(iterator_value.as_object().get(1));
diff --git a/Libraries/LibJS/Runtime/ObjectPrototype.cpp b/Libraries/LibJS/Runtime/ObjectPrototype.cpp
index 1b8828edf9..d24f394a7c 100644
--- a/Libraries/LibJS/Runtime/ObjectPrototype.cpp
+++ b/Libraries/LibJS/Runtime/ObjectPrototype.cpp
@@ -136,11 +136,11 @@ JS_DEFINE_NATIVE_FUNCTION(ObjectPrototype::to_string)
 
     // 1. If the this value is undefined, return "[object Undefined]".
     if (this_value.is_undefined())
-        return PrimitiveString::create(vm, "[object Undefined]"_string);
+        return PrimitiveString::create(vm, "[object Undefined]"_utf16_fly_string);
 
     // 2. If the this value is null, return "[object Null]".
     if (this_value.is_null())
-        return PrimitiveString::create(vm, "[object Null]"_string);
+        return PrimitiveString::create(vm, "[object Null]"_utf16_fly_string);
 
     // 3. Let O be ! ToObject(this value).
     auto object = MUST(this_value.to_object(vm));
diff --git a/Libraries/LibJS/Runtime/PrimitiveString.cpp b/Libraries/LibJS/Runtime/PrimitiveString.cpp
index 3e5ad361e9..58df4609ad 100644
--- a/Libraries/LibJS/Runtime/PrimitiveString.cpp
+++ b/Libraries/LibJS/Runtime/PrimitiveString.cpp
@@ -5,7 +5,6 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/Array.h>
 #include <AK/CharacterTypes.h>
 #include <AK/FlyString.h>
 #include <AK/StringBuilder.h>
@@ -55,11 +54,12 @@ GC::Ptr<PrimitiveString> PrimitiveString::try_create_short_flat_concatenated_str
     if (byte_count > String::MAX_SHORT_STRING_BYTE_COUNT)
         return nullptr;
 
-    AK::Array<u8, String::MAX_SHORT_STRING_BYTE_COUNT> buffer;
-    lhs_view->bytes().copy_to({ buffer.data(), lhs_view->length() });
-    rhs_view->bytes().copy_to({ buffer.data() + lhs_view->length(), rhs_view->length() });
+    auto string = Utf16String::create_uninitialized_ascii(byte_count, [&](Bytes buffer) {
+        lhs_view->bytes().copy_to(buffer.slice(0, lhs_view->length()));
+        rhs_view->bytes().copy_to(buffer.slice(lhs_view->length()));
+    });
 
-    return PrimitiveString::create(vm, String::from_utf8_without_validation({ buffer.data(), byte_count }));
+    return PrimitiveString::create(vm, string);
 }
 
 GC::Ref<PrimitiveString> PrimitiveString::create(VM& vm, Utf16String const& string)
@@ -98,21 +98,6 @@ GC::Ref<PrimitiveString> PrimitiveString::create(VM& vm, Utf16FlyString const& s
     return create(vm, string.to_utf16_string());
 }
 
-GC::Ref<PrimitiveString> PrimitiveString::create(VM& vm, String const& string)
-{
-    return create(vm, Utf16String::from_utf8(string.bytes_as_string_view()));
-}
-
-GC::Ref<PrimitiveString> PrimitiveString::create(VM& vm, StringView string)
-{
-    return create(vm, String::from_utf8(string).release_value());
-}
-
-GC::Ref<PrimitiveString> PrimitiveString::create(VM& vm, FlyString const& string)
-{
-    return create(vm, string.to_string());
-}
-
 GC::Ref<PrimitiveString> PrimitiveString::create_from_unsigned_integer(VM& vm, u64 number)
 {
     if (number < vm.numeric_string_cache().size()) {
diff --git a/Libraries/LibJS/Runtime/PrimitiveString.h b/Libraries/LibJS/Runtime/PrimitiveString.h
index 41884677fd..46f768c5bc 100644
--- a/Libraries/LibJS/Runtime/PrimitiveString.h
+++ b/Libraries/LibJS/Runtime/PrimitiveString.h
@@ -31,10 +31,6 @@ public:
     [[nodiscard]] static GC::Ref<PrimitiveString> create(VM&, Utf16View const&);
     [[nodiscard]] static GC::Ref<PrimitiveString> create(VM&, Utf16FlyString const&);
 
-    [[nodiscard]] static GC::Ref<PrimitiveString> create(VM&, String const&);
-    [[nodiscard]] static GC::Ref<PrimitiveString> create(VM&, StringView);
-    [[nodiscard]] static GC::Ref<PrimitiveString> create(VM&, FlyString const&);
-
     [[nodiscard]] static GC::Ref<PrimitiveString> create(VM&, PrimitiveString&, PrimitiveString&);
     [[nodiscard]] static GC::Ref<PrimitiveString> create(VM&, PrimitiveString const&, size_t code_unit_offset, size_t code_unit_length);
 
diff --git a/Libraries/LibJS/Runtime/Promise.cpp b/Libraries/LibJS/Runtime/Promise.cpp
index 6605356997..3ab92c48f7 100644
--- a/Libraries/LibJS/Runtime/Promise.cpp
+++ b/Libraries/LibJS/Runtime/Promise.cpp
@@ -76,7 +76,7 @@ Promise::ResolvingFunctions Promise::create_resolving_functions()
 
     // 27.2.1.3.2 Promise Resolve Functions, https://tc39.es/ecma262/#sec-promise-resolve-functions
     auto resolve_function = PromiseResolvingFunction::create_resolve(realm, *this);
-    resolve_function->define_direct_property(vm.names.name, PrimitiveString::create(vm, String {}), Attribute::Configurable);
+    resolve_function->define_direct_property(vm.names.name, PrimitiveString::create(vm, Utf16String {}), Attribute::Configurable);
 
     // 7. Let stepsReject be the algorithm steps defined in Promise Reject Functions.
     // 8. Let lengthReject be the number of non-optional parameters of the function definition in Promise Reject Functions.
@@ -86,7 +86,7 @@ Promise::ResolvingFunctions Promise::create_resolving_functions()
 
     // 27.2.1.3.1 Promise Reject Functions, https://tc39.es/ecma262/#sec-promise-reject-functions
     auto reject_function = PromiseResolvingFunction::create_reject(realm, *this, resolve_function);
-    reject_function->define_direct_property(vm.names.name, PrimitiveString::create(vm, String {}), Attribute::Configurable);
+    reject_function->define_direct_property(vm.names.name, PrimitiveString::create(vm, Utf16String {}), Attribute::Configurable);
 
     // 12. Return the Record { [[Resolve]]: resolve, [[Reject]]: reject }.
     return { *resolve_function, *reject_function };
@@ -120,7 +120,7 @@ Value Promise::resolve_function_steps(VM& vm, Promise& promise, bool& already_re
         dbgln_if(PROMISE_DEBUG, "[Promise @ {} / PromiseResolvingFunction]: Promise can't be resolved with itself, rejecting with error", &promise);
 
         // a. Let selfResolutionError be a newly created TypeError object.
-        auto self_resolution_error = TypeError::create(realm, "Cannot resolve promise with itself"sv);
+        auto self_resolution_error = TypeError::create(realm, "Cannot resolve promise with itself"_utf16);
 
         // b. Perform RejectPromise(promise, selfResolutionError).
         promise.reject(self_resolution_error);
diff --git a/Libraries/LibJS/Runtime/PromiseConstructor.cpp b/Libraries/LibJS/Runtime/PromiseConstructor.cpp
index d524a10aa3..f2e6ca7186 100644
--- a/Libraries/LibJS/Runtime/PromiseConstructor.cpp
+++ b/Libraries/LibJS/Runtime/PromiseConstructor.cpp
@@ -119,7 +119,7 @@ static ThrowCompletionOr<Value> perform_promise_all(VM& vm, IteratorRecord& iter
             // p. Set onFulfilled.[[Capability]] to resultCapability.
             // q. Set onFulfilled.[[RemainingElements]] to remainingElementsCount.
             auto on_fulfilled = PromiseAllResolveElementFunction::create(realm, index, values, result_capability, remaining_elements_count);
-            on_fulfilled->define_direct_property(vm.names.name, PrimitiveString::create(vm, String {}), Attribute::Configurable);
+            on_fulfilled->define_direct_property(vm.names.name, PrimitiveString::create(vm, Utf16String {}), Attribute::Configurable);
 
             // s. Perform ? Invoke(nextPromise, "then", « onFulfilled, resultCapability.[[Reject]] »).
             return next_promise.invoke(vm, vm.names.then, on_fulfilled, result_capability.reject());
@@ -151,7 +151,7 @@ static ThrowCompletionOr<Value> perform_promise_all_settled(VM& vm, IteratorReco
             // q. Set onFulfilled.[[Capability]] to resultCapability.
             // r. Set onFulfilled.[[RemainingElements]] to remainingElementsCount.
             auto on_fulfilled = PromiseAllSettledResolveElementFunction::create(realm, index, values, result_capability, remaining_elements_count);
-            on_fulfilled->define_direct_property(vm.names.name, PrimitiveString::create(vm, String {}), Attribute::Configurable);
+            on_fulfilled->define_direct_property(vm.names.name, PrimitiveString::create(vm, Utf16String {}), Attribute::Configurable);
 
             // s. Let stepsRejected be the algorithm steps defined in Promise.allSettled Reject Element Functions.
             // t. Let lengthRejected be the number of non-optional parameters of the function definition in Promise.allSettled Reject Element Functions.
@@ -162,7 +162,7 @@ static ThrowCompletionOr<Value> perform_promise_all_settled(VM& vm, IteratorReco
             // y. Set onRejected.[[Capability]] to resultCapability.
             // z. Set onRejected.[[RemainingElements]] to remainingElementsCount.
             auto on_rejected = PromiseAllSettledRejectElementFunction::create(realm, index, values, result_capability, remaining_elements_count);
-            on_rejected->define_direct_property(vm.names.name, PrimitiveString::create(vm, String {}), Attribute::Configurable);
+            on_rejected->define_direct_property(vm.names.name, PrimitiveString::create(vm, Utf16String {}), Attribute::Configurable);
 
             // ab. Perform ? Invoke(nextPromise, "then", « onFulfilled, onRejected »).
             return next_promise.invoke(vm, vm.names.then, on_fulfilled, on_rejected);
@@ -198,7 +198,7 @@ static ThrowCompletionOr<Value> perform_promise_any(VM& vm, IteratorRecord& iter
             // p. Set onRejected.[[Capability]] to resultCapability.
             // q. Set onRejected.[[RemainingElements]] to remainingElementsCount.
             auto on_rejected = PromiseAnyRejectElementFunction::create(realm, index, errors, result_capability, remaining_elements_count);
-            on_rejected->define_direct_property(vm.names.name, PrimitiveString::create(vm, String {}), Attribute::Configurable);
+            on_rejected->define_direct_property(vm.names.name, PrimitiveString::create(vm, Utf16String {}), Attribute::Configurable);
 
             // s. Perform ? Invoke(nextPromise, "then", « resultCapability.[[Resolve]], onRejected »).
             return next_promise.invoke(vm, vm.names.then, result_capability.resolve(), on_rejected);
diff --git a/Libraries/LibJS/Runtime/PromiseResolvingElementFunctions.cpp b/Libraries/LibJS/Runtime/PromiseResolvingElementFunctions.cpp
index e8133de405..4488af97ff 100644
--- a/Libraries/LibJS/Runtime/PromiseResolvingElementFunctions.cpp
+++ b/Libraries/LibJS/Runtime/PromiseResolvingElementFunctions.cpp
@@ -117,7 +117,7 @@ ThrowCompletionOr<Value> PromiseAllSettledResolveElementFunction::resolve_elemen
     auto object = Object::create(realm, realm.intrinsics().object_prototype());
 
     // 10. Perform ! CreateDataPropertyOrThrow(obj, "status", "fulfilled").
-    MUST(object->create_data_property_or_throw(vm.names.status, PrimitiveString::create(vm, "fulfilled"_string)));
+    MUST(object->create_data_property_or_throw(vm.names.status, PrimitiveString::create(vm, "fulfilled"_utf16_fly_string)));
 
     // 11. Perform ! CreateDataPropertyOrThrow(obj, "value", x).
     MUST(object->create_data_property_or_throw(vm.names.value, vm.argument(0)));
@@ -158,7 +158,7 @@ ThrowCompletionOr<Value> PromiseAllSettledRejectElementFunction::resolve_element
     auto object = Object::create(realm, realm.intrinsics().object_prototype());
 
     // 10. Perform ! CreateDataPropertyOrThrow(obj, "status", "rejected").
-    MUST(object->create_data_property_or_throw(vm.names.status, PrimitiveString::create(vm, "rejected"_string)));
+    MUST(object->create_data_property_or_throw(vm.names.status, PrimitiveString::create(vm, "rejected"_utf16_fly_string)));
 
     // 11. Perform ! CreateDataPropertyOrThrow(obj, "reason", x).
     MUST(object->create_data_property_or_throw(vm.names.reason, vm.argument(0)));
diff --git a/Libraries/LibJS/Runtime/RegExpObject.cpp b/Libraries/LibJS/Runtime/RegExpObject.cpp
index c2f67e1237..18e723f01a 100644
--- a/Libraries/LibJS/Runtime/RegExpObject.cpp
+++ b/Libraries/LibJS/Runtime/RegExpObject.cpp
@@ -44,7 +44,7 @@ struct RegExpNameElement {
 
 static ParseRegexPatternError invalid_group_name_error()
 {
-    return ParseRegexPatternError { "invalid group name"_string };
+    return ParseRegexPatternError { "invalid group name"_utf16 };
 }
 
 static ErrorOr<RegExpNameElement, ParseRegexPatternError> parse_regexp_name_element(Utf16View const& pattern, size_t index)
@@ -231,7 +231,7 @@ static ErrorOr<void, ParseRegexPatternError> validate_named_group_name_surrogate
 
 }
 
-static Result<RegExpObject::Flags, String> validate_flags(Utf16View const& flags)
+static Result<RegExpObject::Flags, Utf16String> validate_flags(Utf16View const& flags)
 {
     bool seen[128] {};
     RegExpObject::Flags flag_bits = static_cast<RegExpObject::Flags>(0);
@@ -240,22 +240,22 @@ static Result<RegExpObject::Flags, String> validate_flags(Utf16View const& flags
         auto ch = flags.code_unit_at(index);
 
         switch (ch) {
-#define __JS_ENUMERATE(FlagName, flagName, flag_name, flag_char)                              \
-    case #flag_char[0]:                                                                       \
-        if (seen[ch])                                                                         \
-            return MUST(String::formatted(ErrorType::RegExpObjectRepeatedFlag.format(), ch)); \
-        seen[ch] = true;                                                                      \
-        flag_bits |= RegExpObject::Flags::FlagName;                                           \
+#define __JS_ENUMERATE(FlagName, flagName, flag_name, flag_char)                             \
+    case #flag_char[0]:                                                                      \
+        if (seen[ch])                                                                        \
+            return Utf16String::formatted(ErrorType::RegExpObjectRepeatedFlag.format(), ch); \
+        seen[ch] = true;                                                                     \
+        flag_bits |= RegExpObject::Flags::FlagName;                                          \
         break;
             JS_ENUMERATE_REGEXP_FLAGS
 #undef __JS_ENUMERATE
         default:
-            return MUST(String::formatted(ErrorType::RegExpObjectBadFlag.format(), ch));
+            return Utf16String::formatted(ErrorType::RegExpObjectBadFlag.format(), ch);
         }
     }
 
     if (has_flag(flag_bits, RegExpObject::Flags::Unicode) && has_flag(flag_bits, RegExpObject::Flags::UnicodeSets))
-        return MUST(String::formatted(ErrorType::RegExpObjectIncompatibleFlags.format(), 'u', 'v'));
+        return Utf16String::formatted(ErrorType::RegExpObjectIncompatibleFlags.format(), 'u', 'v');
 
     return flag_bits;
 }
@@ -264,7 +264,7 @@ static Result<RegExpObject::Flags, String> validate_flags(Utf16View const& flags
 ErrorOr<Utf16String, ParseRegexPatternError> parse_regex_pattern(Utf16View const& pattern, bool unicode, bool unicode_sets)
 {
     if (unicode && unicode_sets)
-        return ParseRegexPatternError { MUST(String::formatted(ErrorType::RegExpObjectIncompatibleFlags.format(), 'u', 'v')) };
+        return ParseRegexPatternError { Utf16String::formatted(ErrorType::RegExpObjectIncompatibleFlags.format(), 'u', 'v') };
 
     TRY(validate_named_group_name_surrogates(pattern, unicode || unicode_sets));
 
diff --git a/Libraries/LibJS/Runtime/RegExpObject.h b/Libraries/LibJS/Runtime/RegExpObject.h
index 6760b70795..82ef113a9d 100644
--- a/Libraries/LibJS/Runtime/RegExpObject.h
+++ b/Libraries/LibJS/Runtime/RegExpObject.h
@@ -20,7 +20,7 @@ JS_API ThrowCompletionOr<GC::Ref<RegExpObject>> regexp_create(VM&, Value pattern
 ThrowCompletionOr<GC::Ref<RegExpObject>> regexp_alloc(VM&, FunctionObject& new_target);
 
 struct ParseRegexPatternError {
-    String error;
+    Utf16String error;
 };
 ErrorOr<Utf16String, ParseRegexPatternError> parse_regex_pattern(Utf16View const& pattern, bool unicode, bool unicode_sets);
 ThrowCompletionOr<Utf16String> parse_regex_pattern(VM& vm, Utf16View const& pattern, bool unicode, bool unicode_sets);
diff --git a/Libraries/LibJS/Runtime/RegExpPrototype.cpp b/Libraries/LibJS/Runtime/RegExpPrototype.cpp
index ebfffa2f14..aa59315f71 100644
--- a/Libraries/LibJS/Runtime/RegExpPrototype.cpp
+++ b/Libraries/LibJS/Runtime/RegExpPrototype.cpp
@@ -1141,7 +1141,7 @@ JS_DEFINE_NATIVE_FUNCTION(RegExpPrototype::source)
     if (!is<RegExpObject>(*regexp_object)) {
         // a. If SameValue(R, %RegExp.prototype%) is true, return "(?:)".
         if (same_value(regexp_object, realm.intrinsics().regexp_prototype()))
-            return PrimitiveString::create(vm, "(?:)"_string);
+            return PrimitiveString::create(vm, "(?:)"_utf16_fly_string);
 
         // b. Otherwise, throw a TypeError exception.
         return vm.throw_completion<TypeError>(ErrorType::NotAnObjectOfType, "RegExp");
@@ -1553,7 +1553,7 @@ JS_DEFINE_NATIVE_FUNCTION(RegExpPrototype::to_string)
 
     // 5. Let result be the string-concatenation of "/", pattern, "/", and flags.
     // 6. Return result.
-    return PrimitiveString::create(vm, ByteString::formatted("/{}/{}", pattern, flags));
+    return PrimitiveString::create(vm, Utf16String::formatted("/{}/{}", pattern, flags));
 }
 
 // B.2.4.1 RegExp.prototype.compile ( pattern, flags ), https://tc39.es/ecma262/#sec-regexp.prototype.compile
diff --git a/Libraries/LibJS/Runtime/RegExpStringIteratorPrototype.cpp b/Libraries/LibJS/Runtime/RegExpStringIteratorPrototype.cpp
index 15ff08b7e2..672fa8b50f 100644
--- a/Libraries/LibJS/Runtime/RegExpStringIteratorPrototype.cpp
+++ b/Libraries/LibJS/Runtime/RegExpStringIteratorPrototype.cpp
@@ -28,7 +28,7 @@ void RegExpStringIteratorPrototype::initialize(Realm& realm)
     define_native_function(realm, vm.names.next, next, 0, attr);
 
     // 22.2.9.2.2 %RegExpStringIteratorPrototype% [ @@toStringTag ], https://tc39.es/ecma262/#sec-%regexpstringiteratorprototype%-@@tostringtag
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "RegExp String Iterator"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "RegExp String Iterator"_utf16_fly_string), Attribute::Configurable);
 }
 
 // 22.2.9.2.1 %RegExpStringIteratorPrototype%.next ( ), https://tc39.es/ecma262/#sec-%regexpstringiteratorprototype%.next
diff --git a/Libraries/LibJS/Runtime/SetIteratorPrototype.cpp b/Libraries/LibJS/Runtime/SetIteratorPrototype.cpp
index 22da8ed2f0..01fdda8ad1 100644
--- a/Libraries/LibJS/Runtime/SetIteratorPrototype.cpp
+++ b/Libraries/LibJS/Runtime/SetIteratorPrototype.cpp
@@ -28,7 +28,7 @@ void SetIteratorPrototype::initialize(Realm& realm)
     define_native_function(realm, vm.names.next, next, 0, Attribute::Configurable | Attribute::Writable, Bytecode::Builtin::SetIteratorPrototypeNext);
 
     // 24.2.5.2.2 %SetIteratorPrototype% [ @@toStringTag ], https://tc39.es/ecma262/#sec-%setiteratorprototype%-@@tostringtag
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Set Iterator"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Set Iterator"_utf16_fly_string), Attribute::Configurable);
 }
 
 // 24.2.5.2.1 %SetIteratorPrototype%.next ( ), https://tc39.es/ecma262/#sec-%setiteratorprototype%.next
diff --git a/Libraries/LibJS/Runtime/StringConstructor.cpp b/Libraries/LibJS/Runtime/StringConstructor.cpp
index f3972e45f6..cd6515b990 100644
--- a/Libraries/LibJS/Runtime/StringConstructor.cpp
+++ b/Libraries/LibJS/Runtime/StringConstructor.cpp
@@ -49,7 +49,7 @@ ThrowCompletionOr<Value> StringConstructor::call()
 
     // 1. If value is not present, let s be the empty String.
     if (!vm.argument_count())
-        return PrimitiveString::create(vm, String {});
+        return PrimitiveString::create(vm, Utf16String {});
 
     // 2. Else,
     // a. If NewTarget is undefined and value is a Symbol, return SymbolDescriptiveString(value).
@@ -72,7 +72,7 @@ ThrowCompletionOr<GC::Ref<Object>> StringConstructor::construct(FunctionObject&
 
     // 1. If value is not present, let s be the empty String.
     if (!vm.argument_count()) {
-        primitive_string = PrimitiveString::create(vm, String {});
+        primitive_string = PrimitiveString::create(vm, Utf16String {});
     }
     // 2. Else,
     else {
@@ -169,7 +169,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringConstructor::raw)
 
     // 5. If literalCount ≤ 0, return the empty String.
     if (literal_count == 0)
-        return PrimitiveString::create(vm, String {});
+        return PrimitiveString::create(vm, Utf16String {});
 
     // 6. Let R be the empty String.
     Utf16StringBuilder builder;
diff --git a/Libraries/LibJS/Runtime/StringIteratorPrototype.cpp b/Libraries/LibJS/Runtime/StringIteratorPrototype.cpp
index 4163ab278a..c690cf3a53 100644
--- a/Libraries/LibJS/Runtime/StringIteratorPrototype.cpp
+++ b/Libraries/LibJS/Runtime/StringIteratorPrototype.cpp
@@ -26,7 +26,7 @@ void StringIteratorPrototype::initialize(Realm& realm)
     define_native_function(realm, vm.names.next, next, 0, Attribute::Configurable | Attribute::Writable, Bytecode::Builtin::StringIteratorPrototypeNext);
 
     // 22.1.5.1.2 %StringIteratorPrototype% [ @@toStringTag ], https://tc39.es/ecma262/#sec-%stringiteratorprototype%-@@tostringtag
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "String Iterator"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "String Iterator"_utf16_fly_string), Attribute::Configurable);
 }
 
 // 22.1.5.1.1 %StringIteratorPrototype%.next ( ), https://tc39.es/ecma262/#sec-%stringiteratorprototype%.next
diff --git a/Libraries/LibJS/Runtime/StringPrototype.cpp b/Libraries/LibJS/Runtime/StringPrototype.cpp
index 43115d4e6d..8e28243365 100644
--- a/Libraries/LibJS/Runtime/StringPrototype.cpp
+++ b/Libraries/LibJS/Runtime/StringPrototype.cpp
@@ -273,7 +273,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::char_at)
     // 4. Let size be the length of S.
     // 5. If position < 0 or position ≥ size, return the empty String.
     if (position < 0 || position >= string->length_in_utf16_code_units())
-        return PrimitiveString::create(vm, String {});
+        return PrimitiveString::create(vm, Utf16String {});
 
     // 6. Return the substring of S from position to position + 1.
     return PrimitiveString::create(vm, *string, position, 1);
@@ -687,7 +687,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::match_all)
     auto string = TRY(this_object.to_primitive_string(vm));
 
     // 4. Let rx be ? RegExpCreate(regexp, "g").
-    auto rx = TRY(regexp_create(vm, regexp, PrimitiveString::create(vm, "g"_string)));
+    auto rx = TRY(regexp_create(vm, regexp, PrimitiveString::create(vm, "g"_utf16_fly_string)));
 
     // 5. Return ? Invoke(rx, @@matchAll, « S »).
     return TRY(Value(rx).invoke(vm, vm.well_known_symbol_match_all(), string));
@@ -769,8 +769,8 @@ static ThrowCompletionOr<Value> pad_string(VM& vm, GC::Ref<PrimitiveString> stri
     // 10. If placement is start, return the string-concatenation of truncatedStringFiller and S.
     // 11. Else, return the string-concatenation of S and truncatedStringFiller.
     auto formatted = placement == PadPlacement::Start
-        ? MUST(String::formatted("{}{}", truncated_string_filler, string->utf16_string_view()))
-        : MUST(String::formatted("{}{}", string->utf16_string_view(), truncated_string_filler));
+        ? Utf16String::formatted("{}{}", truncated_string_filler, string->utf16_string_view())
+        : Utf16String::formatted("{}{}", string->utf16_string_view(), truncated_string_filler);
     return PrimitiveString::create(vm, move(formatted));
 }
 
@@ -1122,7 +1122,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::slice)
 
     // 12. If from ≥ to, return the empty String.
     if (int_start >= int_end)
-        return PrimitiveString::create(vm, String {});
+        return PrimitiveString::create(vm, Utf16String {});
 
     // 13. Return the substring of S from from to to.
     return PrimitiveString::create(vm, *string, int_start, int_end - int_start);
@@ -1347,7 +1347,7 @@ static ThrowCompletionOr<Utf16String> transform_case(VM& vm, Utf16String const&
     // 1. Let requestedLocales be ? CanonicalizeLocaleList(locales).
     auto requested_locales = TRY(Intl::canonicalize_locale_list(vm, locales));
 
-    String requested_locale;
+    Utf16String requested_locale;
 
     // 2. If requestedLocales is not an empty List, then
     if (!requested_locales.is_empty()) {
@@ -1357,7 +1357,7 @@ static ThrowCompletionOr<Utf16String> transform_case(VM& vm, Utf16String const&
     // 3. Else,
     else {
         // a. Let requestedLocale be ! DefaultLocale().
-        requested_locale = String::from_utf8_without_validation(Unicode::default_locale().bytes());
+        requested_locale = Utf16String::from_utf16(Unicode::default_locale());
     }
 
     // 4. Let availableLocales be an Available Locales List which includes the language tags for which the Unicode Character Database contains language-sensitive case mappings. If the implementation supports additional locale-sensitive case mappings, availableLocales should also include their corresponding language tags.
@@ -1365,7 +1365,7 @@ static ThrowCompletionOr<Utf16String> transform_case(VM& vm, Utf16String const&
     auto match = Intl::lookup_matching_locale_by_prefix({ { requested_locale } });
 
     // 6. If match is not undefined, let locale be match.[[locale]]; else let locale be "und".
-    StringView locale = match.has_value() ? match->locale : "und"sv;
+    auto locale = match.has_value() ? match->locale.utf16_view().bytes() : "und"sv;
 
     // 7. Let codePoints be StringToCodePoints(S).
 
@@ -1573,7 +1573,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::substr)
     auto int_end = min((i32)(int_start + int_length), size);
 
     if (int_start >= int_end)
-        return PrimitiveString::create(vm, String {});
+        return PrimitiveString::create(vm, Utf16String {});
 
     // 11. Return the substring of S from intStart to intEnd.
     return PrimitiveString::create(vm, *string, int_start, int_end - int_start);
diff --git a/Libraries/LibJS/Runtime/SuppressedErrorPrototype.cpp b/Libraries/LibJS/Runtime/SuppressedErrorPrototype.cpp
index 65da8d2455..7aa83e0bbe 100644
--- a/Libraries/LibJS/Runtime/SuppressedErrorPrototype.cpp
+++ b/Libraries/LibJS/Runtime/SuppressedErrorPrototype.cpp
@@ -22,8 +22,8 @@ void SuppressedErrorPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
     Base::initialize(realm);
     u8 attr = Attribute::Writable | Attribute::Configurable;
-    define_direct_property(vm.names.name, PrimitiveString::create(vm, "SuppressedError"_string), attr);
-    define_direct_property(vm.names.message, PrimitiveString::create(vm, String {}), attr);
+    define_direct_property(vm.names.name, PrimitiveString::create(vm, "SuppressedError"_utf16_fly_string), attr);
+    define_direct_property(vm.names.message, PrimitiveString::create(vm, Utf16String {}), attr);
 }
 
 }
diff --git a/Libraries/LibJS/Runtime/SymbolPrototype.cpp b/Libraries/LibJS/Runtime/SymbolPrototype.cpp
index c5e835fa66..9dd142ac7e 100644
--- a/Libraries/LibJS/Runtime/SymbolPrototype.cpp
+++ b/Libraries/LibJS/Runtime/SymbolPrototype.cpp
@@ -36,7 +36,7 @@ void SymbolPrototype::initialize(Realm& realm)
     define_native_function(realm, vm.well_known_symbol_to_primitive(), symbol_to_primitive, 1, Attribute::Configurable);
 
     // 20.4.3.6 Symbol.prototype [ @@toStringTag ], https://tc39.es/ecma262/#sec-symbol.prototype-@@tostringtag
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Symbol"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Symbol"_utf16_fly_string), Attribute::Configurable);
 }
 
 // thisSymbolValue ( value ), https://tc39.es/ecma262/#thissymbolvalue
diff --git a/Libraries/LibJS/Runtime/Temporal/AbstractOperations.cpp b/Libraries/LibJS/Runtime/Temporal/AbstractOperations.cpp
index d0d1c92189..5e5b2b1dcd 100644
--- a/Libraries/LibJS/Runtime/Temporal/AbstractOperations.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/AbstractOperations.cpp
@@ -8,6 +8,7 @@
  */
 
 #include <AK/NeverDestroyed.h>
+#include <AK/StringBuilder.h>
 #include <AK/Utf16String.h>
 #include <AK/Utf16StringBuilder.h>
 #include <LibCrypto/BigFraction/BigFraction.h>
@@ -48,9 +49,31 @@ static auto temporal_units = to_array<TemporalUnit>({
     { Unit::Nanosecond, "nanosecond"sv, "nanoseconds"sv, UnitCategory::Time, 1000 },
 });
 
-StringView temporal_unit_to_string(Unit unit)
+Utf16View temporal_unit_to_string(Unit unit)
 {
-    return temporal_units[to_underlying(unit)].singular_property_name;
+    switch (unit) {
+    case Unit::Year:
+        return u"year"sv;
+    case Unit::Month:
+        return u"month"sv;
+    case Unit::Week:
+        return u"week"sv;
+    case Unit::Day:
+        return u"day"sv;
+    case Unit::Hour:
+        return u"hour"sv;
+    case Unit::Minute:
+        return u"minute"sv;
+    case Unit::Second:
+        return u"second"sv;
+    case Unit::Millisecond:
+        return u"millisecond"sv;
+    case Unit::Microsecond:
+        return u"microsecond"sv;
+    case Unit::Nanosecond:
+        return u"nanosecond"sv;
+    }
+    VERIFY_NOT_REACHED();
 }
 
 // 13.1 ISODateToEpochDays ( year, month, date ), https://tc39.es/proposal-temporal/#sec-isodatetoepochdays
@@ -87,7 +110,7 @@ ThrowCompletionOr<void> check_iso_days_range(VM& vm, ISODate iso_date)
 ThrowCompletionOr<Overflow> get_temporal_overflow_option(VM& vm, Object const& options)
 {
     // 1. Let stringValue be ? GetOption(options, "overflow", STRING, « "constrain", "reject" », "constrain").
-    auto string_value = TRY(get_option(vm, options, vm.names.overflow, OptionType::String, { "constrain"sv, "reject"sv }, "constrain"sv));
+    auto string_value = TRY(get_option(vm, options, vm.names.overflow, OptionType::String, { "constrain"sv, "reject"sv }, u"constrain"sv));
 
     // 2. If stringValue is "constrain", return CONSTRAIN.
     if (string_value.as_string().utf16_string_view() == "constrain"sv)
@@ -101,7 +124,7 @@ ThrowCompletionOr<Overflow> get_temporal_overflow_option(VM& vm, Object const& o
 ThrowCompletionOr<Disambiguation> get_temporal_disambiguation_option(VM& vm, Object const& options)
 {
     // 1. Let stringValue be ? GetOption(options, "disambiguation", STRING, « "compatible", "earlier", "later", "reject" », "compatible").
-    auto string_value = TRY(get_option(vm, options, vm.names.disambiguation, OptionType::String, { "compatible"sv, "earlier"sv, "later"sv, "reject"sv }, "compatible"sv));
+    auto string_value = TRY(get_option(vm, options, vm.names.disambiguation, OptionType::String, { "compatible"sv, "earlier"sv, "later"sv, "reject"sv }, u"compatible"sv));
     auto string_view = string_value.as_string().utf16_string_view();
 
     // 2. If stringValue is "compatible", return COMPATIBLE.
@@ -150,16 +173,16 @@ ThrowCompletionOr<OffsetOption> get_temporal_offset_option(VM& vm, Object const&
         switch (fallback) {
         // 1. If fallback is PREFER, let stringFallback be "prefer".
         case OffsetOption::Prefer:
-            return "prefer"sv;
+            return u"prefer"sv;
         // 2. Else if fallback is USE, let stringFallback be "use".
         case OffsetOption::Use:
-            return "use"sv;
+            return u"use"sv;
         // 3. Else if fallback is IGNORE, let stringFallback be "ignore".
         case OffsetOption::Ignore:
-            return "ignore"sv;
+            return u"ignore"sv;
         // 4. Else, let stringFallback be "reject".
         case OffsetOption::Reject:
-            return "reject"sv;
+            return u"reject"sv;
         }
         VERIFY_NOT_REACHED();
     }();
@@ -188,7 +211,7 @@ ThrowCompletionOr<OffsetOption> get_temporal_offset_option(VM& vm, Object const&
 ThrowCompletionOr<ShowCalendar> get_temporal_show_calendar_name_option(VM& vm, Object const& options)
 {
     // 1. Let stringValue be ? GetOption(options, "calendarName", STRING, « "auto", "always", "never", "critical" », "auto").
-    auto string_value = TRY(get_option(vm, options, vm.names.calendarName, OptionType::String, { "auto"sv, "always"sv, "never"sv, "critical"sv }, "auto"sv));
+    auto string_value = TRY(get_option(vm, options, vm.names.calendarName, OptionType::String, { "auto"sv, "always"sv, "never"sv, "critical"sv }, u"auto"sv));
     auto string_view = string_value.as_string().utf16_string_view();
 
     // 2. If stringValue is "always", return ALWAYS.
@@ -211,7 +234,7 @@ ThrowCompletionOr<ShowCalendar> get_temporal_show_calendar_name_option(VM& vm, O
 ThrowCompletionOr<ShowTimeZoneName> get_temporal_show_time_zone_name_option(VM& vm, Object const& options)
 {
     // 1. Let stringValue be ? GetOption(options, "timeZoneName", STRING, « "auto", "never", "critical" », "auto").
-    auto string_value = TRY(get_option(vm, options, vm.names.timeZoneName, OptionType::String, { "auto"sv, "never"sv, "critical"sv }, "auto"sv));
+    auto string_value = TRY(get_option(vm, options, vm.names.timeZoneName, OptionType::String, { "auto"sv, "never"sv, "critical"sv }, u"auto"sv));
     auto string_view = string_value.as_string().utf16_string_view();
 
     // 2. If stringValue is "never", return NEVER.
@@ -230,7 +253,7 @@ ThrowCompletionOr<ShowTimeZoneName> get_temporal_show_time_zone_name_option(VM&
 ThrowCompletionOr<ShowOffset> get_temporal_show_offset_option(VM& vm, Object const& options)
 {
     // 1. Let stringValue be ? GetOption(options, "offset", STRING, « "auto", "never" », "auto").
-    auto string_value = TRY(get_option(vm, options, vm.names.offset, OptionType::String, { "auto"sv, "never"sv }, "auto"sv));
+    auto string_value = TRY(get_option(vm, options, vm.names.offset, OptionType::String, { "auto"sv, "never"sv }, u"auto"sv));
     auto string_view = string_value.as_string().utf16_string_view();
 
     // 2. If stringValue is "never", return never.
@@ -405,7 +428,7 @@ ThrowCompletionOr<UnitValue> get_temporal_unit_valued_option(VM& vm, Object cons
     auto default_value = default_.visit(
         [](Unset) -> OptionDefault { return Empty {}; },
         [](Required) -> OptionDefault { return Required {}; },
-        [](Auto) -> OptionDefault { return "auto"sv; },
+        [](Auto) -> OptionDefault { return u"auto"sv; },
         [](Unit unit) -> OptionDefault { return temporal_unit_to_string(unit); });
 
     // 6. Let value be ? GetOption(options, key, STRING, allowedStrings, defaultValue).
@@ -478,8 +501,8 @@ ThrowCompletionOr<RelativeTo> get_temporal_relative_to_option(VM& vm, Object con
     // 4. Let matchBehaviour be MATCH-EXACTLY.
     auto match_behavior = MatchBehavior::MatchExactly;
 
-    String calendar;
-    Optional<String> time_zone;
+    Utf16String calendar;
+    Optional<Utf16String> time_zone;
     Optional<Utf16String> offset_string;
 
     ISODate iso_date;
@@ -595,7 +618,7 @@ ThrowCompletionOr<RelativeTo> get_temporal_relative_to_option(VM& vm, Object con
         if (result.calendar.has_value())
             calendar = TRY(canonicalize_calendar(vm, *result.calendar));
         else
-            calendar = TRY(canonicalize_calendar(vm, "iso8601"sv));
+            calendar = TRY(canonicalize_calendar(vm, ISO8601_CALENDAR));
 
         // j. Let isoDate be CreateISODateRecord(result.[[Year]], result.[[Month]], result.[[Day]]).
         iso_date = create_iso_date_record(*result.year, result.month, result.day);
@@ -1336,7 +1359,7 @@ ThrowCompletionOr<Utf16String> parse_temporal_calendar_string(VM& vm, Utf16View
 
         // b. If calendar is EMPTY, return "iso8601".
         // c. Else, return calendar.
-        return calendar.value_or(Utf16String::from_utf8_without_validation("iso8601"sv));
+        return calendar.value_or("iso8601"_utf16);
     }
 
     // 3. Set parseResult to ParseText(StringToCodePoints(string), AnnotationValue).
@@ -1631,7 +1654,7 @@ ThrowCompletionOr<Utf16String> to_offset_string(VM& vm, Value argument)
 }
 
 // 13.42 ISODateToFields ( calendar, isoDate, type ), https://tc39.es/proposal-temporal/#sec-temporal-isodatetofields
-CalendarFields iso_date_to_fields(String const& calendar, ISODate iso_date, DateType type)
+CalendarFields iso_date_to_fields(Utf16View calendar, ISODate iso_date, DateType type)
 {
     // 1. Let fields be an empty Calendar Fields Record with all fields set to unset.
     auto fields = CalendarFields::unset();
diff --git a/Libraries/LibJS/Runtime/Temporal/AbstractOperations.h b/Libraries/LibJS/Runtime/Temporal/AbstractOperations.h
index 32ab735cc8..b0014af2f4 100644
--- a/Libraries/LibJS/Runtime/Temporal/AbstractOperations.h
+++ b/Libraries/LibJS/Runtime/Temporal/AbstractOperations.h
@@ -8,6 +8,7 @@
 
 #pragma once
 
+#include <AK/Utf16View.h>
 #include <AK/Variant.h>
 #include <LibCrypto/BigInt/SignedBigInteger.h>
 #include <LibCrypto/BigInt/UnsignedBigInteger.h>
@@ -99,7 +100,7 @@ enum class Unit {
     Microsecond,
     Nanosecond,
 };
-StringView temporal_unit_to_string(Unit);
+Utf16View temporal_unit_to_string(Unit);
 
 // https://tc39.es/proposal-temporal/#sec-temporal-units
 enum class UnitCategory {
@@ -196,7 +197,7 @@ ThrowCompletionOr<Utf16String> parse_temporal_calendar_string(VM&, Utf16View);
 ThrowCompletionOr<GC::Ref<Duration>> parse_temporal_duration_string(VM&, Utf16View iso_string);
 ThrowCompletionOr<ParsedTimeZoneIdentifier> parse_temporal_time_zone_string(VM&, Utf16View time_zone_string);
 ThrowCompletionOr<Utf16String> to_offset_string(VM&, Value argument);
-CalendarFields iso_date_to_fields(String const& calendar, ISODate, DateType);
+CalendarFields iso_date_to_fields(Utf16View calendar, ISODate, DateType);
 ThrowCompletionOr<DifferenceSettings> get_difference_settings(VM&, DurationOperation, Object const& options, UnitGroup, ReadonlySpan<Unit> disallowed_units, Unit fallback_smallest_unit, Unit smallest_largest_default_unit);
 
 // 13.40 ToIntegerWithTruncation ( argument ), https://tc39.es/proposal-temporal/#sec-tointegerwithtruncation
diff --git a/Libraries/LibJS/Runtime/Temporal/Calendar.cpp b/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
index 0027837b9b..71d34d6df9 100644
--- a/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
@@ -7,6 +7,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/CharacterTypes.h>
 #include <AK/GenericShorthands.h>
 #include <AK/NeverDestroyed.h>
 #include <AK/NonnullRawPtr.h>
@@ -26,7 +27,7 @@
 
 namespace JS::Temporal {
 
-String ISO8601_CALENDAR = "iso8601"_string;
+Utf16String ISO8601_CALENDAR = "iso8601"_utf16;
 
 enum class CalendarFieldConversion {
     ToIntegerWithTruncation,
@@ -119,7 +120,7 @@ static void set_default_field_value(CalendarField field, CalendarFields& fields)
 }
 
 // Table 1: Calendar types described in CLDR, https://tc39.es/proposal-intl-era-monthcode/#table-calendar-types
-static constexpr auto CLDR_CALENDAR_TYPES = to_array({
+static constexpr auto CLDR_CALENDAR_TYPES = to_array<Utf16View>({
     "buddhist"sv,
     "chinese"sv,
     "coptic"sv,
@@ -148,9 +149,9 @@ struct CalendarEraData {
         Negative,
     };
 
-    StringView calendar;
-    StringView era;
-    StringView alias;
+    Utf16View calendar;
+    Utf16View era;
+    Utf16View alias;
     Optional<i32> minimum_era_year;
     Optional<i32> maximum_era_year;
     Kind kind;
@@ -196,14 +197,14 @@ struct AdditionalMonthCodes {
         SkipForward,
     };
 
-    StringView calendar;
-    ReadonlySpan<StringView> additional_month_codes;
+    Utf16View calendar;
+    ReadonlySpan<Utf16View> additional_month_codes;
     Optional<Leap> leap_to_common_month_transformation;
 };
 
-static constexpr auto ALL_LEAP_MONTH_CODES = to_array({ "M01L"sv, "M02L"sv, "M03L"sv, "M04L"sv, "M05L"sv, "M06L"sv, "M07L"sv, "M08L"sv, "M09L"sv, "M10L"sv, "M11L"sv, "M12L"sv });
-static constexpr auto THIRTEENTH_MONTH_CODES = to_array({ "M13"sv });
-static constexpr auto HEBREW_ADAR_I_MONTH_CODES = to_array({ "M05L"sv });
+static constexpr auto ALL_LEAP_MONTH_CODES = to_array<Utf16View>({ "M01L"sv, "M02L"sv, "M03L"sv, "M04L"sv, "M05L"sv, "M06L"sv, "M07L"sv, "M08L"sv, "M09L"sv, "M10L"sv, "M11L"sv, "M12L"sv });
+static constexpr auto THIRTEENTH_MONTH_CODES = to_array<Utf16View>({ "M13"sv });
+static constexpr auto HEBREW_ADAR_I_MONTH_CODES = to_array<Utf16View>({ "M05L"sv });
 
 static constexpr auto ADDITIONAL_MONTH_CODES = to_array<AdditionalMonthCodes>({
     { "chinese"sv, ALL_LEAP_MONTH_CODES, AdditionalMonthCodes::Leap::SkipBackward },
@@ -216,7 +217,7 @@ static constexpr auto ADDITIONAL_MONTH_CODES = to_array<AdditionalMonthCodes>({
 
 // Table 6: "chinese" and "dangi" Calendars ISO Reference Years, https://tc39.es/proposal-intl-era-monthcode/#chinese-dangi-iso-reference-years
 struct ISOReferenceYears {
-    StringView month_code;
+    Utf16View month_code;
     Optional<i32> days_1_to_29;
     Optional<i32> day_30;
 };
@@ -247,9 +248,9 @@ static constexpr auto CHINESE_AND_DANGI_ISO_REFERENCE_YEARS = to_array<ISORefere
     { "M12L"sv, {}, {} },
 });
 
-static Optional<i32> chinese_or_dangi_reference_year(String const& calendar, StringView month_code, u8 day)
+static Optional<i32> chinese_or_dangi_reference_year(Utf16View calendar, Utf16View month_code, u8 day)
 {
-    auto row = find_value(CHINESE_AND_DANGI_ISO_REFERENCE_YEARS, [&](auto const& row) { return row.month_code == month_code; });
+    auto row = find_value(CHINESE_AND_DANGI_ISO_REFERENCE_YEARS, [&](auto const& row) { return month_code == row.month_code; });
     VERIFY(row.has_value());
 
     if (day >= 1 && day < 30) {
@@ -267,47 +268,41 @@ static Optional<i32> chinese_or_dangi_reference_year(String const& calendar, Str
     return {};
 }
 
-// 12.1.1 CanonicalizeCalendar ( id ), https://tc39.es/proposal-temporal/#sec-temporal-canonicalizecalendar
-ThrowCompletionOr<String> canonicalize_calendar(VM& vm, StringView id)
+ThrowCompletionOr<Utf16String> canonicalize_calendar(VM& vm, Utf16View id)
 {
-    // 1. Let calendars be AvailableCalendars().
+    if (!id.is_ascii())
+        return vm.throw_completion<RangeError>(ErrorType::TemporalInvalidCalendarIdentifier, id);
+
     auto const& calendars = available_calendars();
 
-    // 2. If calendars does not contain the ASCII-lowercase of id, throw a RangeError exception.
     for (auto const& calendar : calendars) {
         if (calendar.equals_ignoring_ascii_case(id)) {
-            // 3. Return CanonicalizeUValue("ca", id).
-            return Unicode::canonicalize_unicode_extension_values("ca"sv, id);
+            return Unicode::canonicalize_unicode_extension_values("ca"sv, calendar.utf16_view());
         }
     }
 
     return vm.throw_completion<RangeError>(ErrorType::TemporalInvalidCalendarIdentifier, id);
 }
 
-ThrowCompletionOr<String> canonicalize_calendar(VM& vm, Utf16View id)
-{
-    if (!id.is_ascii())
-        return vm.throw_completion<RangeError>(ErrorType::TemporalInvalidCalendarIdentifier, id);
-
-    auto id_string = MUST(id.to_utf8());
-    return canonicalize_calendar(vm, id_string.bytes_as_string_view());
-}
-
 // 12.1.2 AvailableCalendars ( ), https://tc39.es/proposal-temporal/#sec-availablecalendars
 // 1.1.1 AvailableCalendars ( ), https://tc39.es/proposal-intl-era-monthcode/#sup-availablecalendars
-Vector<String> const& available_calendars()
+Vector<Utf16String> const& available_calendars()
 {
     // The implementation-defined abstract operation AvailableCalendars takes no arguments and returns a List of calendar
     // types. The returned List is sorted according to lexicographic code unit order, and contains unique calendar types
     // in canonical form (12.1) identifying the calendars for which the implementation provides the functionality of
     // Intl.DateTimeFormat objects, including their aliases (e.g., both "islamicc" and "islamic-civil"). The List must
     // consist of the "Calendar Type" value of every row of Table 1, except the header row.
-    static NeverDestroyed<Vector<String>> calendars { []() {
-        auto calendars = Unicode::available_calendars();
+    static NeverDestroyed<Vector<Utf16String>> calendars { []() {
+        Vector<Utf16String> calendars;
+
+        for (auto const& calendar : Unicode::available_calendars())
+            calendars.append(calendar);
 
         for (auto calendar : CLDR_CALENDAR_TYPES) {
-            if (!calendars.contains_slow(calendar))
-                calendars.append(String::from_utf8_without_validation(calendar.bytes()));
+            auto calendar_string = Utf16String::from_utf16(calendar);
+            if (!calendars.contains_slow(calendar_string))
+                calendars.append(move(calendar_string));
         }
 
         quick_sort(calendars);
@@ -330,15 +325,6 @@ ThrowCompletionOr<MonthCode> parse_month_code(VM& vm, Value argument)
     return parse_month_code(vm, month_code.as_string().utf16_string_view());
 }
 
-// 12.2.1 ParseMonthCode ( argument ), https://tc39.es/proposal-temporal/#sec-temporal-parsemonthcode
-ThrowCompletionOr<MonthCode> parse_month_code(VM& vm, StringView month_code)
-{
-    // 3. If ParseText(StringToCodePoints(monthCode), MonthCode) is a List of errors, throw a RangeError exception.
-    if (auto result = Unicode::parse_month_code(month_code); result.has_value())
-        return result.release_value();
-    return vm.throw_completion<RangeError>(ErrorType::TemporalInvalidMonthCode);
-}
-
 // 12.2.1 ParseMonthCode ( argument ), https://tc39.es/proposal-temporal/#sec-temporal-parsemonthcode
 ThrowCompletionOr<MonthCode> parse_month_code(VM& vm, Utf16View month_code)
 {
@@ -349,7 +335,7 @@ ThrowCompletionOr<MonthCode> parse_month_code(VM& vm, Utf16View month_code)
 }
 
 // 12.3.3 PrepareCalendarFields ( calendar, fields, calendarFieldNames, nonCalendarFieldNames, requiredFieldNames ), https://tc39.es/proposal-temporal/#sec-temporal-preparecalendarfields
-ThrowCompletionOr<CalendarFields> prepare_calendar_fields(VM& vm, String const& calendar, Object const& fields, CalendarFieldList calendar_field_names, CalendarFieldList non_calendar_field_names, CalendarFieldListOrPartial required_field_names)
+ThrowCompletionOr<CalendarFields> prepare_calendar_fields(VM& vm, Utf16View calendar, Object const& fields, CalendarFieldList calendar_field_names, CalendarFieldList non_calendar_field_names, CalendarFieldListOrPartial required_field_names)
 {
     // 1. Assert: If requiredFieldNames is a List, requiredFieldNames contains zero or one of each of the elements of
     //    calendarFieldNames and nonCalendarFieldNames.
@@ -478,7 +464,7 @@ Vector<CalendarField> calendar_field_keys_present(CalendarFields const& fields)
 }
 
 // 12.3.5 CalendarMergeFields ( calendar, fields, additionalFields ), https://tc39.es/proposal-temporal/#sec-temporal-calendarmergefields
-CalendarFields calendar_merge_fields(String const& calendar, CalendarFields const& fields, CalendarFields const& additional_fields)
+CalendarFields calendar_merge_fields(Utf16View calendar, CalendarFields const& fields, CalendarFields const& additional_fields)
 {
     // 1. Let additionalKeys be CalendarFieldKeysPresent(additionalFields).
     auto additional_keys = calendar_field_keys_present(additional_fields);
@@ -522,7 +508,7 @@ CalendarFields calendar_merge_fields(String const& calendar, CalendarFields cons
 
 // 12.3.6 NonISODateAdd ( calendar, isoDate, duration, overflow ), https://tc39.es/proposal-temporal/#sec-temporal-nonisodateadd
 // 4.1.18 NonISODateAdd ( calendar, isoDate, duration, overflow ), https://tc39.es/proposal-intl-era-monthcode/#sup-temporal-nonisodateadd
-ThrowCompletionOr<ISODate> non_iso_date_add(VM& vm, String const& calendar, ISODate iso_date, DateDuration const& duration, Overflow overflow)
+ThrowCompletionOr<ISODate> non_iso_date_add(VM& vm, Utf16View calendar, ISODate iso_date, DateDuration const& duration, Overflow overflow)
 {
     // 1. Let parts be CalendarISOToDate(calendar, isoDate).
     auto parts = non_iso_calendar_iso_to_date(calendar, iso_date);
@@ -570,7 +556,7 @@ ThrowCompletionOr<ISODate> non_iso_date_add(VM& vm, String const& calendar, ISOD
 }
 
 // 12.3.7 CalendarDateAdd ( calendar, isoDate, duration, overflow ), https://tc39.es/proposal-temporal/#sec-temporal-calendardateadd
-ThrowCompletionOr<ISODate> calendar_date_add(VM& vm, String const& calendar, ISODate iso_date, DateDuration const& duration, Overflow overflow)
+ThrowCompletionOr<ISODate> calendar_date_add(VM& vm, Utf16View calendar, ISODate iso_date, DateDuration const& duration, Overflow overflow)
 {
     ISODate result;
 
@@ -604,7 +590,7 @@ ThrowCompletionOr<ISODate> calendar_date_add(VM& vm, String const& calendar, ISO
 
 // 12.3.8 NonISODateUntil ( calendar, one, two, largestUnit ), https://tc39.es/proposal-temporal/#sec-temporal-nonisodateuntil
 // 4.1.19 NonISODateUntil ( calendar, one, two, largestUnit ), https://tc39.es/proposal-intl-era-monthcode/#sup-temporal-nonisodateuntil
-DateDuration non_iso_date_until(VM& vm, String const& calendar, ISODate one, ISODate two, Unit largest_unit)
+DateDuration non_iso_date_until(VM& vm, Utf16View calendar, ISODate one, ISODate two, Unit largest_unit)
 {
     // 1. Let sign be -1 × CompareISODate(one, two).
     auto sign = compare_iso_date(one, two);
@@ -709,7 +695,7 @@ DateDuration non_iso_date_until(VM& vm, String const& calendar, ISODate one, ISO
 }
 
 // 12.3.9 CalendarDateUntil ( calendar, one, two, largestUnit ), https://tc39.es/proposal-temporal/#sec-temporal-calendardateuntil
-DateDuration calendar_date_until(VM& vm, String const& calendar, ISODate one, ISODate two, Unit largest_unit)
+DateDuration calendar_date_until(VM& vm, Utf16View calendar, ISODate one, ISODate two, Unit largest_unit)
 {
     // 1. Let sign be CompareISODate(one, two).
     auto sign = compare_iso_date(one, two);
@@ -794,7 +780,7 @@ DateDuration calendar_date_until(VM& vm, String const& calendar, ISODate one, IS
 }
 
 // 12.3.10 ToTemporalCalendarIdentifier ( temporalCalendarLike ), https://tc39.es/proposal-temporal/#sec-temporal-totemporalcalendaridentifier
-ThrowCompletionOr<String> to_temporal_calendar_identifier(VM& vm, Value temporal_calendar_like)
+ThrowCompletionOr<Utf16String> to_temporal_calendar_identifier(VM& vm, Value temporal_calendar_like)
 {
     // 1. If temporalCalendarLike is an Object and temporalCalendarLike has an [[InitializedTemporalDate]],
     //    [[InitializedTemporalDateTime]], [[InitializedTemporalMonthDay]], [[InitializedTemporalYearMonth]], or
@@ -822,7 +808,7 @@ ThrowCompletionOr<String> to_temporal_calendar_identifier(VM& vm, Value temporal
 }
 
 // 12.3.11 GetTemporalCalendarIdentifierWithISODefault ( item ), https://tc39.es/proposal-temporal/#sec-temporal-gettemporalcalendarslotvaluewithisodefault
-ThrowCompletionOr<String> get_temporal_calendar_identifier_with_iso_default(VM& vm, Object const& item)
+ThrowCompletionOr<Utf16String> get_temporal_calendar_identifier_with_iso_default(VM& vm, Object const& item)
 {
     // 1. If item has an [[InitializedTemporalDate]], [[InitializedTemporalDateTime]], [[InitializedTemporalMonthDay]],
     //    [[InitializedTemporalYearMonth]], or [[InitializedTemporalZonedDateTime]] internal slot, then
@@ -843,14 +829,14 @@ ThrowCompletionOr<String> get_temporal_calendar_identifier_with_iso_default(VM&
 
     // 3. If calendarLike is undefined, return "iso8601".
     if (calendar_like.is_undefined())
-        return "iso8601"_string;
+        return "iso8601"_utf16;
 
     // 4. Return ? ToTemporalCalendarIdentifier(calendarLike).
     return TRY(to_temporal_calendar_identifier(vm, calendar_like));
 }
 
 // 12.3.12 CalendarDateFromFields ( calendar, fields, overflow ), https://tc39.es/proposal-temporal/#sec-temporal-calendardatefromfields
-ThrowCompletionOr<ISODate> calendar_date_from_fields(VM& vm, String const& calendar, CalendarFields& fields, Overflow overflow)
+ThrowCompletionOr<ISODate> calendar_date_from_fields(VM& vm, Utf16View calendar, CalendarFields& fields, Overflow overflow)
 {
     // 1. Perform ? CalendarResolveFields(calendar, fields, DATE).
     TRY(calendar_resolve_fields(vm, calendar, fields, DateType::Date));
@@ -867,7 +853,7 @@ ThrowCompletionOr<ISODate> calendar_date_from_fields(VM& vm, String const& calen
 }
 
 // 12.3.13 CalendarYearMonthFromFields ( calendar, fields, overflow ), https://tc39.es/proposal-temporal/#sec-temporal-calendaryearmonthfromfields
-ThrowCompletionOr<ISODate> calendar_year_month_from_fields(VM& vm, String const& calendar, CalendarFields& fields, Overflow overflow)
+ThrowCompletionOr<ISODate> calendar_year_month_from_fields(VM& vm, Utf16View calendar, CalendarFields& fields, Overflow overflow)
 {
     // 1. Set fields.[[Day]] to 1.
     fields.day = 1;
@@ -887,7 +873,7 @@ ThrowCompletionOr<ISODate> calendar_year_month_from_fields(VM& vm, String const&
 }
 
 // 12.3.14 CalendarMonthDayFromFields ( calendar, fields, overflow ), https://tc39.es/proposal-temporal/#sec-temporal-calendarmonthdayfromfields
-ThrowCompletionOr<ISODate> calendar_month_day_from_fields(VM& vm, String const& calendar, CalendarFields& fields, Overflow overflow)
+ThrowCompletionOr<ISODate> calendar_month_day_from_fields(VM& vm, Utf16View calendar, CalendarFields& fields, Overflow overflow)
 {
     // 1. Perform ? CalendarResolveFields(calendar, fields, MONTH-DAY).
     TRY(calendar_resolve_fields(vm, calendar, fields, DateType::MonthDay));
@@ -903,25 +889,25 @@ ThrowCompletionOr<ISODate> calendar_month_day_from_fields(VM& vm, String const&
 }
 
 // 12.3.15 FormatCalendarAnnotation ( id, showCalendar ), https://tc39.es/proposal-temporal/#sec-temporal-formatcalendarannotation
-String format_calendar_annotation(StringView id, ShowCalendar show_calendar)
+Utf16String format_calendar_annotation(Utf16View id, ShowCalendar show_calendar)
 {
     // 1. If showCalendar is NEVER, return the empty String.
     if (show_calendar == ShowCalendar::Never)
-        return String {};
+        return {};
 
     // 2. If showCalendar is AUTO and id is "iso8601", return the empty String.
     if (show_calendar == ShowCalendar::Auto && id == ISO8601_CALENDAR)
-        return String {};
+        return {};
 
     // 3. If showCalendar is CRITICAL, let flag be "!"; else, let flag be the empty String.
     auto flag = show_calendar == ShowCalendar::Critical ? "!"sv : ""sv;
 
     // 4. Return the string-concatenation of "[", flag, "u-ca=", id, and "]".
-    return MUST(String::formatted("[{}u-ca={}]", flag, id));
+    return Utf16String::formatted("[{}u-ca={}]", flag, id);
 }
 
 // 12.3.16 CalendarEquals ( one, two ), https://tc39.es/proposal-temporal/#sec-temporal-calendarequals
-bool calendar_equals(StringView one, StringView two)
+bool calendar_equals(Utf16View one, Utf16View two)
 {
     // 1. If CanonicalizeUValue("ca", one) is CanonicalizeUValue("ca", two), return true.
     // 2. Return false.
@@ -1057,7 +1043,7 @@ u8 iso_day_of_week(ISODate iso_date)
 
 // 12.3.21 NonISOCalendarDateToISO ( calendar, fields, overflow ), https://tc39.es/proposal-temporal/#sec-temporal-nonisocalendardatetoiso
 // 4.1.20 NonISOCalendarDateToISO ( calendar, fields, overflow ), https://tc39.es/proposal-intl-era-monthcode/#sup-temporal-nonisocalendardatetoiso
-ThrowCompletionOr<ISODate> non_iso_calendar_date_to_iso(VM& vm, String const& calendar, CalendarFields const& fields, Overflow overflow)
+ThrowCompletionOr<ISODate> non_iso_calendar_date_to_iso(VM& vm, Utf16View calendar, CalendarFields const& fields, Overflow overflow)
 {
     // 1. Assert: fields.[[Year]], fields.[[Month]], and fields.[[Day]] are not UNSET.
     VERIFY(fields.year.has_value());
@@ -1115,7 +1101,7 @@ ThrowCompletionOr<ISODate> non_iso_calendar_date_to_iso(VM& vm, String const& ca
 }
 
 // 12.3.22 CalendarDateToISO ( calendar, fields, overflow ), https://tc39.es/proposal-temporal/#sec-temporal-calendardatetoiso
-ThrowCompletionOr<ISODate> calendar_date_to_iso(VM& vm, String const& calendar, CalendarFields const& fields, Overflow overflow)
+ThrowCompletionOr<ISODate> calendar_date_to_iso(VM& vm, Utf16View calendar, CalendarFields const& fields, Overflow overflow)
 {
     // 1. If calendar is "iso8601", then
     if (calendar == ISO8601_CALENDAR) {
@@ -1134,7 +1120,7 @@ ThrowCompletionOr<ISODate> calendar_date_to_iso(VM& vm, String const& calendar,
 
 // 12.3.23 NonISOMonthDayToISOReferenceDate ( calendar, fields, overflow ), https://tc39.es/proposal-temporal/#sec-temporal-nonisomonthdaytoisoreferencedate
 // 4.1.21 NonISOMonthDayToISOReferenceDate ( calendar, fields, overflow ), https://tc39.es/proposal-intl-era-monthcode/#sup-temporal-nonisomonthdaytoisoreferencedate
-ThrowCompletionOr<ISODate> non_iso_month_day_to_iso_reference_date(VM& vm, String const& calendar, CalendarFields const& fields, Overflow overflow)
+ThrowCompletionOr<ISODate> non_iso_month_day_to_iso_reference_date(VM& vm, Utf16View calendar, CalendarFields const& fields, Overflow overflow)
 {
     // 1. Assert: fields.[[Day]] is not UNSET.
     VERIFY(fields.day.has_value());
@@ -1142,7 +1128,7 @@ ThrowCompletionOr<ISODate> non_iso_month_day_to_iso_reference_date(VM& vm, Strin
     u8 day = 0;
     u8 month = 0;
     u8 days_in_month = 0;
-    String month_code;
+    Utf16String month_code;
 
     // 2. If fields.[[Year]] is not UNSET, then
     if (fields.year.has_value()) {
@@ -1201,7 +1187,7 @@ ThrowCompletionOr<ISODate> non_iso_month_day_to_iso_reference_date(VM& vm, Strin
 
         // c. If calendar is "chinese" or "dangi", let daysInMonth be 30; else, let daysInMonth be the maximum number of
         //    days in the month described by monthCode in any year.
-        days_in_month = calendar.is_one_of("chinese"sv, "dangi"sv) ? 30 : Unicode::calendar_max_days_in_month_code(calendar, month_code);
+        days_in_month = calendar.is_one_of("chinese"sv, "dangi"sv) ? 30 : Unicode::calendar_max_days_in_month_code(calendar.bytes(), month_code);
     }
 
     // 4. If fields.[[Day]] > daysInMonth, then
@@ -1241,7 +1227,7 @@ ThrowCompletionOr<ISODate> non_iso_month_day_to_iso_reference_date(VM& vm, Strin
 
             // ii. Set monthCode to CreateMonthCode(! ParseMonthCode(monthCode).[[MonthNumber]], false).
             if (month_code.ends_with('L'))
-                month_code = MUST(month_code.trim("L"sv, TrimMode::Right));
+                month_code = month_code.trim("L"sv, TrimMode::Right);
         }
     }
 
@@ -1253,15 +1239,15 @@ ThrowCompletionOr<ISODate> non_iso_month_day_to_iso_reference_date(VM& vm, Strin
     auto result = [&]() -> Optional<ISODate> {
         if (is_chinese_or_dangi) {
             auto reference_year = chinese_or_dangi_reference_year(calendar, month_code, day);
-            return Unicode::iso_year_and_month_code_to_iso_date(calendar, *reference_year, month_code, day);
+            return Unicode::iso_year_and_month_code_to_iso_date(calendar.bytes(), *reference_year, month_code, day);
         }
 
         for (i32 iso_year = 1972; iso_year >= 1900; --iso_year) {
-            if (auto result = Unicode::iso_year_and_month_code_to_iso_date(calendar, iso_year, month_code, day); result.has_value())
+            if (auto result = Unicode::iso_year_and_month_code_to_iso_date(calendar.bytes(), iso_year, month_code, day); result.has_value())
                 return result;
         }
         for (i32 iso_year = 1973; iso_year <= 2035; ++iso_year) {
-            if (auto result = Unicode::iso_year_and_month_code_to_iso_date(calendar, iso_year, month_code, day); result.has_value())
+            if (auto result = Unicode::iso_year_and_month_code_to_iso_date(calendar.bytes(), iso_year, month_code, day); result.has_value())
                 return result;
         }
 
@@ -1273,7 +1259,7 @@ ThrowCompletionOr<ISODate> non_iso_month_day_to_iso_reference_date(VM& vm, Strin
 }
 
 // 12.3.24 CalendarMonthDayToISOReferenceDate ( calendar, fields, overflow ), https://tc39.es/proposal-temporal/#sec-temporal-calendarmonthdaytoisoreferencedate
-ThrowCompletionOr<ISODate> calendar_month_day_to_iso_reference_date(VM& vm, String const& calendar, CalendarFields const& fields, Overflow overflow)
+ThrowCompletionOr<ISODate> calendar_month_day_to_iso_reference_date(VM& vm, Utf16View calendar, CalendarFields const& fields, Overflow overflow)
 {
     // 1. If calendar is "iso8601", then
     if (calendar == ISO8601_CALENDAR) {
@@ -1299,9 +1285,9 @@ ThrowCompletionOr<ISODate> calendar_month_day_to_iso_reference_date(VM& vm, Stri
 }
 
 // 12.3.25 NonISOCalendarISOToDate ( calendar, isoDate ), https://tc39.es/proposal-temporal/#sec-temporal-nonisocalendarisotodate
-CalendarDate non_iso_calendar_iso_to_date(String const& calendar, ISODate iso_date)
+CalendarDate non_iso_calendar_iso_to_date(Utf16View calendar, ISODate iso_date)
 {
-    auto result = Unicode::iso_date_to_calendar_date(calendar, iso_date);
+    auto result = Unicode::iso_date_to_calendar_date(calendar.bytes(), iso_date);
 
     for (auto const& row : CALENDAR_ERA_DATA) {
         if (row.calendar != calendar)
@@ -1328,7 +1314,7 @@ CalendarDate non_iso_calendar_iso_to_date(String const& calendar, ISODate iso_da
         if (row.iso_era_start.has_value() && compare_iso_date(iso_date, *row.iso_era_start) < 0)
             continue;
 
-        result.era = String::from_utf8_without_validation(row.era.bytes());
+        result.era = Utf16String::from_utf16(row.era);
         result.era_year = era_year;
         break;
     }
@@ -1337,7 +1323,7 @@ CalendarDate non_iso_calendar_iso_to_date(String const& calendar, ISODate iso_da
 }
 
 // 12.3.26 CalendarISOToDate ( calendar, isoDate ), https://tc39.es/proposal-temporal/#sec-temporal-calendarisotodate
-CalendarDate calendar_iso_to_date(String const& calendar, ISODate iso_date)
+CalendarDate calendar_iso_to_date(Utf16View calendar, ISODate iso_date)
 {
     // 1. If calendar is "iso8601", then
     if (calendar == ISO8601_CALENDAR) {
@@ -1373,7 +1359,7 @@ CalendarDate calendar_iso_to_date(String const& calendar, ISODate iso_date)
 
 // 12.3.27 CalendarExtraFields ( calendar, fields ), https://tc39.es/proposal-temporal/#sec-temporal-calendarextrafields
 // 4.1.22 CalendarExtraFields ( calendar, fields ), https://tc39.es/proposal-intl-era-monthcode/#sup-temporal-calendarextrafields
-Vector<CalendarField> calendar_extra_fields(String const& calendar, CalendarFieldList fields)
+Vector<CalendarField> calendar_extra_fields(Utf16View calendar, CalendarFieldList fields)
 {
     // 1. If fields contains an element equal to YEAR and CalendarSupportsEra(calendar) is true, then
     if (fields.contains_slow(CalendarField::Year) && calendar_supports_era(calendar)) {
@@ -1387,7 +1373,7 @@ Vector<CalendarField> calendar_extra_fields(String const& calendar, CalendarFiel
 
 // 12.3.28 NonISOFieldKeysToIgnore ( calendar, keys ), https://tc39.es/proposal-temporal/#sec-temporal-nonisofieldkeystoignore
 // 4.1.23 NonISOFieldKeysToIgnore ( calendar, keys ), https://tc39.es/proposal-intl-era-monthcode/#sup-temporal-nonisofieldkeystoignore
-Vector<CalendarField> non_iso_field_keys_to_ignore(String const& calendar, ReadonlySpan<CalendarField> keys)
+Vector<CalendarField> non_iso_field_keys_to_ignore(Utf16View calendar, ReadonlySpan<CalendarField> keys)
 {
     // 1. Let ignoredKeys be a copy of keys.
     Vector<CalendarField> ignored_keys { keys };
@@ -1426,7 +1412,7 @@ Vector<CalendarField> non_iso_field_keys_to_ignore(String const& calendar, Reado
 }
 
 // 12.3.29 CalendarFieldKeysToIgnore ( calendar, keys ), https://tc39.es/proposal-temporal/#sec-temporal-calendarfieldkeystoignore
-Vector<CalendarField> calendar_field_keys_to_ignore(String const& calendar, ReadonlySpan<CalendarField> keys)
+Vector<CalendarField> calendar_field_keys_to_ignore(Utf16View calendar, ReadonlySpan<CalendarField> keys)
 {
     // 1. If calendar is "iso8601", then
     if (calendar == ISO8601_CALENDAR) {
@@ -1459,7 +1445,7 @@ Vector<CalendarField> calendar_field_keys_to_ignore(String const& calendar, Read
 
 // 12.3.30 NonISOResolveFields ( calendar, fields, type ), https://tc39.es/proposal-temporal/#sec-temporal-nonisoresolvefields
 // 4.1.24 NonISOResolveFields ( calendar, fields, type ), https://tc39.es/proposal-intl-era-monthcode/#sup-temporal-nonisoresolvefields
-ThrowCompletionOr<void> non_iso_resolve_fields(VM& vm, String const& calendar, CalendarFields& fields, DateType type)
+ThrowCompletionOr<void> non_iso_resolve_fields(VM& vm, Utf16View calendar, CalendarFields& fields, DateType type)
 {
     // 1. Let needsYear be false.
     // 2. If type is DATE or type is YEAR-MONTH, set needsYear to true.
@@ -1593,7 +1579,7 @@ ThrowCompletionOr<void> non_iso_resolve_fields(VM& vm, String const& calendar, C
 }
 
 // 12.3.31 CalendarResolveFields ( calendar, fields, type ), https://tc39.es/proposal-temporal/#sec-temporal-calendarresolvefields
-ThrowCompletionOr<void> calendar_resolve_fields(VM& vm, String const& calendar, CalendarFields& fields, DateType type)
+ThrowCompletionOr<void> calendar_resolve_fields(VM& vm, Utf16View calendar, CalendarFields& fields, DateType type)
 {
     // 1. If calendar is "iso8601", then
     if (calendar == ISO8601_CALENDAR) {
@@ -1652,7 +1638,7 @@ ThrowCompletionOr<void> calendar_resolve_fields(VM& vm, String const& calendar,
 }
 
 // 4.1.1 CalendarSupportsEra ( calendar ), https://tc39.es/proposal-intl-era-monthcode/#sec-temporal-calendarsupportsera
-bool calendar_supports_era(String const& calendar)
+bool calendar_supports_era(Utf16View calendar)
 {
     // 1. If calendar is listed in the "Calendar" column of Table 2, return true.
     // 2. If calendar is listed in the "Calendar Type" column of Table 1, return false.
@@ -1661,7 +1647,7 @@ bool calendar_supports_era(String const& calendar)
 }
 
 // 4.1.2 CanonicalizeEraInCalendar ( calendar, era ), https://tc39.es/proposal-intl-era-monthcode/#sec-temporal-canonicalizeeraincalendar
-Optional<StringView> canonicalize_era_in_calendar(String const& calendar, Utf16View era)
+Optional<Utf16View> canonicalize_era_in_calendar(Utf16View calendar, Utf16View era)
 {
     // 1. For each row of Table 2, except the header row, do
     for (auto const& row : CALENDAR_ERA_DATA) {
@@ -1688,7 +1674,7 @@ Optional<StringView> canonicalize_era_in_calendar(String const& calendar, Utf16V
 }
 
 // 4.1.3 CalendarHasMidYearEras ( calendar ), https://tc39.es/proposal-intl-era-monthcode/#sec-temporal-calendarhasmidyeareras
-bool calendar_has_mid_year_eras(String const& calendar)
+bool calendar_has_mid_year_eras(Utf16View calendar)
 {
     // 1. If calendar is "japanese", return true.
     // 2. If calendar is listed in the "Calendar Type" column of Table 1, return false.
@@ -1697,7 +1683,7 @@ bool calendar_has_mid_year_eras(String const& calendar)
 }
 
 // 4.1.4 IsValidMonthCodeForCalendar ( calendar, monthCode ), https://tc39.es/proposal-intl-era-monthcode/#sec-temporal-isvalidmonthcodeforcalendar
-bool is_valid_month_code_for_calendar(String const& calendar, StringView month_code)
+bool is_valid_month_code_for_calendar(Utf16View calendar, Utf16View month_code)
 {
     // 1. Let commonMonthCodes be « "M01", "M02", "M03", "M04", "M05", "M06", "M07", "M08", "M09", "M10", "M11", "M12" ».
     // 2. If commonMonthCodes contains monthCode, return true.
@@ -1710,7 +1696,7 @@ bool is_valid_month_code_for_calendar(String const& calendar, StringView month_c
         // b. Let specialMonthCodes be a List whose elements are the strings given in the "Additional Month Codes" column of r.
         // c. If specialMonthCodes contains monthCode, return true.
         // d. Return false.
-        return row->additional_month_codes.contains_slow(month_code);
+        return any_of(row->additional_month_codes, [&](auto additional_month_code) { return month_code == additional_month_code; });
     }
 
     // 4. If calendar is listed in the "Calendar Type" column of Table 1, return false.
@@ -1719,7 +1705,7 @@ bool is_valid_month_code_for_calendar(String const& calendar, StringView month_c
 }
 
 // 4.1.5 YearContainsMonthCode ( calendar, arithmeticYear, monthCode ), https://tc39.es/proposal-intl-era-monthcode/#sec-temporal-yearcontainsmonthcode
-bool year_contains_month_code(String const& calendar, i32 arithmetic_year, StringView month_code)
+bool year_contains_month_code(Utf16View calendar, i32 arithmetic_year, Utf16View month_code)
 {
     // 1. Assert: IsValidMonthCodeForCalendar(calendar, monthCode) is true.
     VERIFY(is_valid_month_code_for_calendar(calendar, month_code));
@@ -1730,11 +1716,11 @@ bool year_contains_month_code(String const& calendar, i32 arithmetic_year, Strin
 
     // 3. Return whether the leap month indicated by monthCode exists in the year arithmeticYear in calendar, using
     //    calendar-dependent behaviour.
-    return Unicode::calendar_year_contains_month_code(calendar, arithmetic_year, month_code);
+    return Unicode::calendar_year_contains_month_code(calendar.bytes(), arithmetic_year, month_code);
 }
 
 // 4.1.6 ConstrainMonthCode ( calendar, arithmeticYear, monthCode, overflow ), https://tc39.es/proposal-intl-era-monthcode/#sec-temporal-constrainmonthcode
-ThrowCompletionOr<String> constrain_month_code(VM& vm, String const& calendar, i32 arithmetic_year, String const& month_code, Overflow overflow)
+ThrowCompletionOr<Utf16String> constrain_month_code(VM& vm, Utf16View calendar, i32 arithmetic_year, Utf16String const& month_code, Overflow overflow)
 {
     // 1. Assert: IsValidMonthCodeForCalendar(calendar, monthCode) is true.
     VERIFY(is_valid_month_code_for_calendar(calendar, month_code));
@@ -1756,19 +1742,19 @@ ThrowCompletionOr<String> constrain_month_code(VM& vm, String const& calendar, i
     // 7. If shiftType is SKIP-BACKWARD, then
     if (row->leap_to_common_month_transformation == AdditionalMonthCodes::Leap::SkipBackward) {
         // a. Return CreateMonthCode(! ParseMonthCode(monthCode).[[MonthNumber]], false).
-        return MUST(month_code.trim("L"sv, TrimMode::Right));
+        return month_code.trim("L"sv, TrimMode::Right);
     }
 
     // 8. Else,
     // a. Assert: monthCode is "M05L".
-    VERIFY(month_code == "M05L");
+    VERIFY(month_code == "M05L"sv);
 
     // b. Return "M06".
-    return "M06"_string;
+    return "M06"_utf16;
 }
 
 // 4.1.7 MonthCodeToOrdinal ( calendar, arithmeticYear, monthCode ), https://tc39.es/proposal-intl-era-monthcode/#sec-temporal-monthcodetoordinal
-u8 month_code_to_ordinal(String const& calendar, i32 arithmetic_year, StringView month_code)
+u8 month_code_to_ordinal(Utf16View calendar, i32 arithmetic_year, Utf16View month_code)
 {
     // 1. Assert: YearContainsMonthCode(calendar, arithmeticYear, monthCode) is true.
     VERIFY(year_contains_month_code(calendar, arithmetic_year, month_code));
@@ -1792,8 +1778,8 @@ u8 month_code_to_ordinal(String const& calendar, i32 arithmetic_year, StringView
     }
 
     // 7. Assert: The "Additional Month Codes" column of r does not contain "M00L" or "M13".
-    VERIFY(!row->additional_month_codes.contains_slow("M00L"sv));
-    VERIFY(!row->additional_month_codes.contains_slow("M13"sv));
+    VERIFY(!row->additional_month_codes.contains_slow(Utf16View { "M00L"sv }));
+    VERIFY(!row->additional_month_codes.contains_slow(Utf16View { "M13"sv }));
 
     // 8. Assert: This algorithm will return before the following loop terminates by failing its condition.
 
@@ -1827,15 +1813,15 @@ u8 month_code_to_ordinal(String const& calendar, i32 arithmetic_year, StringView
 }
 
 // 4.1.8 CalendarDaysInMonth ( calendar, arithmeticYear, ordinalMonth ), https://tc39.es/proposal-intl-era-monthcode/#sec-temporal-calendardaysinmonth
-u8 calendar_days_in_month(String const& calendar, i32 arithmetic_year, u8 ordinal_month)
+u8 calendar_days_in_month(Utf16View calendar, i32 arithmetic_year, u8 ordinal_month)
 {
     // 1. Let isoDate be ! CalendarIntegersToISO(calendar, arithmeticYear, ordinalMonth, 1).
     // 2. Return CalendarISOToDate(calendar, isoDate).[[DaysInMonth]].
-    return Unicode::calendar_days_in_month(calendar, arithmetic_year, ordinal_month);
+    return Unicode::calendar_days_in_month(calendar.bytes(), arithmetic_year, ordinal_month);
 }
 
 // 4.1.12 CalendarDateArithmeticYearForEraYear ( calendar, era, eraYear ), https://tc39.es/proposal-intl-era-monthcode/#sec-temporal-calendardatearithmeticyearforerayear
-i32 calendar_date_arithmetic_year_for_era_year(String const& calendar, Utf16View era, i32 era_year)
+i32 calendar_date_arithmetic_year_for_era_year(Utf16View calendar, Utf16View era, i32 era_year)
 {
     // 1. Let era be CanonicalizeEraInCalendar(calendar, era).
     // 2. Assert: era is not undefined.
@@ -1876,28 +1862,28 @@ i32 calendar_date_arithmetic_year_for_era_year(String const& calendar, Utf16View
 }
 
 // 4.1.13 CalendarIntegersToISO ( calendar, arithmeticYear, ordinalMonth, day ), https://tc39.es/proposal-intl-era-monthcode/#sec-temporal-calendarintegerstoiso
-ThrowCompletionOr<ISODate> calendar_integers_to_iso(VM& vm, String const& calendar, i32 arithmetic_year, u8 ordinal_month, u8 day)
+ThrowCompletionOr<ISODate> calendar_integers_to_iso(VM& vm, Utf16View calendar, i32 arithmetic_year, u8 ordinal_month, u8 day)
 {
     // 1. If arithmeticYear, ordinalMonth, and day do not form a valid date in calendar, throw a RangeError exception.
     // 2. Let isoDate be an ISO Date Record such that CalendarISOToDate(calendar, isoDate) returns a Calendar Date Record
     //    whose [[Year]], [[Month]], and [[Day]] field values respectively equal arithmeticYear, ordinalMonth, and day.
     // 3. NOTE: No known calendars have repeated dates that would cause isoDate to be ambiguous between two ISO Date Records.
     // 4. Return isoDate.
-    if (auto iso_date = Unicode::calendar_date_to_iso_date(calendar, arithmetic_year, ordinal_month, day); iso_date.has_value())
+    if (auto iso_date = Unicode::calendar_date_to_iso_date(calendar.bytes(), arithmetic_year, ordinal_month, day); iso_date.has_value())
         return create_iso_date_record(iso_date->year, iso_date->month, iso_date->day);
     return vm.throw_completion<RangeError>(ErrorType::TemporalInvalidISODate);
 }
 
 // 4.1.15 CalendarMonthsInYear ( calendar, arithmeticYear ), https://tc39.es/proposal-intl-era-monthcode/#sec-temporal-calendarmonthsinyear
-u8 calendar_months_in_year(String const& calendar, i32 arithmetic_year)
+u8 calendar_months_in_year(Utf16View calendar, i32 arithmetic_year)
 {
     // 1. Let isoDate be ! CalendarIntegersToISO(calendar, arithmeticYear, 1, 1).
     // 2. Return CalendarISOToDate(calendar, isoDate).[[MonthsInYear]].
-    return Unicode::calendar_months_in_year(calendar, arithmetic_year);
+    return Unicode::calendar_months_in_year(calendar.bytes(), arithmetic_year);
 }
 
 // 4.1.16 BalanceNonISODate ( calendar, arithmeticYear, ordinalMonth, day ), https://tc39.es/proposal-intl-era-monthcode/#sec-temporal-balancenonisodate
-BalancedDate balance_non_iso_date(String const& calendar, i32 arithmetic_year, i32 ordinal_month, i32 day)
+BalancedDate balance_non_iso_date(Utf16View calendar, i32 arithmetic_year, i32 ordinal_month, i32 day)
 {
     // 1. Let resolvedYear be arithmeticYear.
     auto resolved_year = arithmetic_year;
@@ -1992,7 +1978,7 @@ BalancedDate balance_non_iso_date(String const& calendar, i32 arithmetic_year, i
 
 // 4.1.17 NonISODateSurpasses ( calendar, sign, fromIsoDate, toIsoDate, years, months, weeks, days ), https://tc39.es/proposal-intl-era-monthcode/#sec-temporal-nonisodatesurpasses
 // NB: The only caller to this function is NonISODateUntil, which precomputes the calendar dates.
-bool non_iso_date_surpasses(VM& vm, String const& calendar, i8 sign, CalendarDate const& from_calendar_date, CalendarDate const& to_calendar_date, double years, double months, double weeks, double days)
+bool non_iso_date_surpasses(VM& vm, Utf16View calendar, i8 sign, CalendarDate const& from_calendar_date, CalendarDate const& to_calendar_date, double years, double months, double weeks, double days)
 {
     // 1. Let parts be CalendarISOToDate(calendar, fromIsoDate).
     auto const& parts = from_calendar_date;
diff --git a/Libraries/LibJS/Runtime/Temporal/Calendar.h b/Libraries/LibJS/Runtime/Temporal/Calendar.h
index 754fd2db37..14acfd4909 100644
--- a/Libraries/LibJS/Runtime/Temporal/Calendar.h
+++ b/Libraries/LibJS/Runtime/Temporal/Calendar.h
@@ -21,7 +21,7 @@
 
 namespace JS::Temporal {
 
-extern String ISO8601_CALENDAR;
+extern Utf16String ISO8601_CALENDAR;
 
 // 12.2 Month Codes, https://tc39.es/proposal-temporal/#sec-temporal-month-codes
 using MonthCode = Unicode::MonthCode;
@@ -76,7 +76,7 @@ struct CalendarFields {
     Optional<i32> era_year;
     Optional<i32> year;
     Optional<u32> month;
-    Optional<String> month_code;
+    Optional<Utf16String> month_code;
     Optional<u32> day;
     Optional<u8> hour { 0 };
     Optional<u8> minute { 0 };
@@ -85,7 +85,7 @@ struct CalendarFields {
     Optional<u16> microsecond { 0 };
     Optional<u16> nanosecond { 0 };
     Optional<Utf16String> offset_string;
-    Optional<String> time_zone;
+    Optional<Utf16String> time_zone;
 };
 
 struct Partial { };
@@ -98,56 +98,54 @@ struct BalancedDate {
     u8 day { 0 };
 };
 
-ThrowCompletionOr<String> canonicalize_calendar(VM&, StringView id);
-ThrowCompletionOr<String> canonicalize_calendar(VM&, Utf16View id);
-Vector<String> const& available_calendars();
+ThrowCompletionOr<Utf16String> canonicalize_calendar(VM&, Utf16View id);
+Vector<Utf16String> const& available_calendars();
 
 ThrowCompletionOr<MonthCode> parse_month_code(VM&, Value argument);
-ThrowCompletionOr<MonthCode> parse_month_code(VM&, StringView month_code);
 ThrowCompletionOr<MonthCode> parse_month_code(VM&, Utf16View month_code);
 
-ThrowCompletionOr<CalendarFields> prepare_calendar_fields(VM&, String const& calendar, Object const& fields, CalendarFieldList calendar_field_names, CalendarFieldList non_calendar_field_names, CalendarFieldListOrPartial required_field_names);
-ThrowCompletionOr<ISODate> calendar_date_from_fields(VM&, String const& calendar, CalendarFields&, Overflow);
-ThrowCompletionOr<ISODate> calendar_year_month_from_fields(VM&, String const& calendar, CalendarFields&, Overflow);
-ThrowCompletionOr<ISODate> calendar_month_day_from_fields(VM&, String const& calendar, CalendarFields&, Overflow);
-String format_calendar_annotation(StringView id, ShowCalendar);
-bool calendar_equals(StringView one, StringView two);
+ThrowCompletionOr<CalendarFields> prepare_calendar_fields(VM&, Utf16View calendar, Object const& fields, CalendarFieldList calendar_field_names, CalendarFieldList non_calendar_field_names, CalendarFieldListOrPartial required_field_names);
+ThrowCompletionOr<ISODate> calendar_date_from_fields(VM&, Utf16View calendar, CalendarFields&, Overflow);
+ThrowCompletionOr<ISODate> calendar_year_month_from_fields(VM&, Utf16View calendar, CalendarFields&, Overflow);
+ThrowCompletionOr<ISODate> calendar_month_day_from_fields(VM&, Utf16View calendar, CalendarFields&, Overflow);
+Utf16String format_calendar_annotation(Utf16View id, ShowCalendar);
+bool calendar_equals(Utf16View one, Utf16View two);
 u8 iso_days_in_month(double year, double month);
 YearWeek iso_week_of_year(ISODate);
 u16 iso_day_of_year(ISODate);
 u8 iso_day_of_week(ISODate);
 Vector<CalendarField> calendar_field_keys_present(CalendarFields const&);
-CalendarFields calendar_merge_fields(String const& calendar, CalendarFields const& fields, CalendarFields const& additional_fields);
-ThrowCompletionOr<ISODate> non_iso_date_add(VM&, String const& calendar, ISODate, DateDuration const&, Overflow);
-ThrowCompletionOr<ISODate> calendar_date_add(VM&, String const& calendar, ISODate, DateDuration const&, Overflow);
-DateDuration non_iso_date_until(VM&, String const& calendar, ISODate, ISODate, Unit largest_unit);
-DateDuration calendar_date_until(VM&, String const& calendar, ISODate, ISODate, Unit largest_unit);
-ThrowCompletionOr<String> to_temporal_calendar_identifier(VM&, Value temporal_calendar_like);
-ThrowCompletionOr<String> get_temporal_calendar_identifier_with_iso_default(VM&, Object const& item);
-ThrowCompletionOr<ISODate> non_iso_calendar_date_to_iso(VM&, String const& calendar, CalendarFields const&, Overflow);
-ThrowCompletionOr<ISODate> calendar_date_to_iso(VM&, String const& calendar, CalendarFields const&, Overflow);
-ThrowCompletionOr<ISODate> non_iso_month_day_to_iso_reference_date(VM&, String const& calendar, CalendarFields const&, Overflow);
-ThrowCompletionOr<ISODate> calendar_month_day_to_iso_reference_date(VM&, String const& calendar, CalendarFields const&, Overflow);
-CalendarDate non_iso_calendar_iso_to_date(String const& calendar, ISODate);
-CalendarDate calendar_iso_to_date(String const& calendar, ISODate);
-Vector<CalendarField> calendar_extra_fields(String const& calendar, CalendarFieldList);
-Vector<CalendarField> non_iso_field_keys_to_ignore(String const& calendar, ReadonlySpan<CalendarField>);
-Vector<CalendarField> calendar_field_keys_to_ignore(String const& calendar, ReadonlySpan<CalendarField>);
-ThrowCompletionOr<void> non_iso_resolve_fields(VM&, String const& calendar, CalendarFields&, DateType);
-ThrowCompletionOr<void> calendar_resolve_fields(VM&, String const& calendar, CalendarFields&, DateType);
+CalendarFields calendar_merge_fields(Utf16View calendar, CalendarFields const& fields, CalendarFields const& additional_fields);
+ThrowCompletionOr<ISODate> non_iso_date_add(VM&, Utf16View calendar, ISODate, DateDuration const&, Overflow);
+ThrowCompletionOr<ISODate> calendar_date_add(VM&, Utf16View calendar, ISODate, DateDuration const&, Overflow);
+DateDuration non_iso_date_until(VM&, Utf16View calendar, ISODate, ISODate, Unit largest_unit);
+DateDuration calendar_date_until(VM&, Utf16View calendar, ISODate, ISODate, Unit largest_unit);
+ThrowCompletionOr<Utf16String> to_temporal_calendar_identifier(VM&, Value temporal_calendar_like);
+ThrowCompletionOr<Utf16String> get_temporal_calendar_identifier_with_iso_default(VM&, Object const& item);
+ThrowCompletionOr<ISODate> non_iso_calendar_date_to_iso(VM&, Utf16View calendar, CalendarFields const&, Overflow);
+ThrowCompletionOr<ISODate> calendar_date_to_iso(VM&, Utf16View calendar, CalendarFields const&, Overflow);
+ThrowCompletionOr<ISODate> non_iso_month_day_to_iso_reference_date(VM&, Utf16View calendar, CalendarFields const&, Overflow);
+ThrowCompletionOr<ISODate> calendar_month_day_to_iso_reference_date(VM&, Utf16View calendar, CalendarFields const&, Overflow);
+CalendarDate non_iso_calendar_iso_to_date(Utf16View calendar, ISODate);
+CalendarDate calendar_iso_to_date(Utf16View calendar, ISODate);
+Vector<CalendarField> calendar_extra_fields(Utf16View calendar, CalendarFieldList);
+Vector<CalendarField> non_iso_field_keys_to_ignore(Utf16View calendar, ReadonlySpan<CalendarField>);
+Vector<CalendarField> calendar_field_keys_to_ignore(Utf16View calendar, ReadonlySpan<CalendarField>);
+ThrowCompletionOr<void> non_iso_resolve_fields(VM&, Utf16View calendar, CalendarFields&, DateType);
+ThrowCompletionOr<void> calendar_resolve_fields(VM&, Utf16View calendar, CalendarFields&, DateType);
 
-bool calendar_supports_era(String const& calendar);
-Optional<StringView> canonicalize_era_in_calendar(String const& calendar, Utf16View era);
-bool calendar_has_mid_year_eras(String const& calendar);
-bool is_valid_month_code_for_calendar(String const& calendar, StringView month_code);
-bool year_contains_month_code(String const& calendar, i32 arithmetic_year, StringView month_code);
-ThrowCompletionOr<String> constrain_month_code(VM&, String const& calendar, i32 arithmetic_year, String const& month_code, Overflow overflow);
-u8 month_code_to_ordinal(String const& calendar, i32 arithmetic_year, StringView month_code);
-u8 calendar_days_in_month(String const& calendar, i32 arithmetic_year, u8 ordinal_month);
-i32 calendar_date_arithmetic_year_for_era_year(String const& calendar, Utf16View era, i32 era_year);
-ThrowCompletionOr<ISODate> calendar_integers_to_iso(VM&, String const& calendar, i32 arithmetic_year, u8 ordinal_month, u8 day);
-u8 calendar_months_in_year(String const& calendar, i32 arithmetic_year);
-BalancedDate balance_non_iso_date(String const& calendar, i32 arithmetic_year, i32 ordinal_month, i32 day);
-bool non_iso_date_surpasses(VM&, String const& calendar, i8 sign, CalendarDate const& from_calendar_date, CalendarDate const& to_calendar_date, double years, double months, double weeks, double days);
+bool calendar_supports_era(Utf16View calendar);
+Optional<Utf16View> canonicalize_era_in_calendar(Utf16View calendar, Utf16View era);
+bool calendar_has_mid_year_eras(Utf16View calendar);
+bool is_valid_month_code_for_calendar(Utf16View calendar, Utf16View month_code);
+bool year_contains_month_code(Utf16View calendar, i32 arithmetic_year, Utf16View month_code);
+ThrowCompletionOr<Utf16String> constrain_month_code(VM&, Utf16View calendar, i32 arithmetic_year, Utf16String const& month_code, Overflow overflow);
+u8 month_code_to_ordinal(Utf16View calendar, i32 arithmetic_year, Utf16View month_code);
+u8 calendar_days_in_month(Utf16View calendar, i32 arithmetic_year, u8 ordinal_month);
+i32 calendar_date_arithmetic_year_for_era_year(Utf16View calendar, Utf16View era, i32 era_year);
+ThrowCompletionOr<ISODate> calendar_integers_to_iso(VM&, Utf16View calendar, i32 arithmetic_year, u8 ordinal_month, u8 day);
+u8 calendar_months_in_year(Utf16View calendar, i32 arithmetic_year);
+BalancedDate balance_non_iso_date(Utf16View calendar, i32 arithmetic_year, i32 ordinal_month, i32 day);
+bool non_iso_date_surpasses(VM&, Utf16View calendar, i8 sign, CalendarDate const& from_calendar_date, CalendarDate const& to_calendar_date, double years, double months, double weeks, double days);
 
 }
diff --git a/Libraries/LibJS/Runtime/Temporal/Duration.cpp b/Libraries/LibJS/Runtime/Temporal/Duration.cpp
index 5265ddd18c..20f0739abc 100644
--- a/Libraries/LibJS/Runtime/Temporal/Duration.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/Duration.cpp
@@ -846,7 +846,7 @@ Crypto::BigFraction total_time_duration(TimeDuration const& time_duration, Unit
 }
 
 // 7.5.33 ComputeNudgeWindow ( sign, duration, originEpochNs, isoDateTime, timeZone, calendar, increment, unit, additionalShift ), https://tc39.es/proposal-temporal/#sec-temporal-computenudgewindow
-ThrowCompletionOr<NudgeWindow> compute_nudge_window(VM& vm, i8 sign, InternalDuration const& duration, Crypto::SignedBigInteger const& origin_epoch_ns, ISODateTime const& iso_date_time, Optional<String const&> time_zone, String const& calendar, u64 increment, Unit unit, bool additional_shift)
+ThrowCompletionOr<NudgeWindow> compute_nudge_window(VM& vm, i8 sign, InternalDuration const& duration, Crypto::SignedBigInteger const& origin_epoch_ns, ISODateTime const& iso_date_time, Optional<Utf16View> time_zone, Utf16View calendar, u64 increment, Unit unit, bool additional_shift)
 {
     DateDuration start_date_duration;
     DateDuration end_date_duration;
@@ -1009,7 +1009,7 @@ ThrowCompletionOr<NudgeWindow> compute_nudge_window(VM& vm, i8 sign, InternalDur
 }
 
 // 7.5.34 NudgeToCalendarUnit ( sign, duration, originEpochNs, destEpochNs, isoDateTime, timeZone, calendar, increment, unit, roundingMode ), https://tc39.es/proposal-temporal/#sec-temporal-nudgetocalendarunit
-ThrowCompletionOr<CalendarNudgeResult> nudge_to_calendar_unit(VM& vm, i8 sign, InternalDuration const& duration, Crypto::SignedBigInteger const& origin_epoch_ns, Crypto::SignedBigInteger const& dest_epoch_ns, ISODateTime const& iso_date_time, Optional<String const&> time_zone, String const& calendar, u64 increment, Unit unit, RoundingMode rounding_mode)
+ThrowCompletionOr<CalendarNudgeResult> nudge_to_calendar_unit(VM& vm, i8 sign, InternalDuration const& duration, Crypto::SignedBigInteger const& origin_epoch_ns, Crypto::SignedBigInteger const& dest_epoch_ns, ISODateTime const& iso_date_time, Optional<Utf16View> time_zone, Utf16View calendar, u64 increment, Unit unit, RoundingMode rounding_mode)
 {
     // 1. Let didExpandCalendarUnit be false.
     auto did_expand_calendar_unit = false;
@@ -1157,7 +1157,7 @@ ThrowCompletionOr<CalendarNudgeResult> nudge_to_calendar_unit(VM& vm, i8 sign, I
 }
 
 // 7.5.35 NudgeToZonedTime ( sign, duration, isoDateTime, timeZone, calendar, increment, unit, roundingMode ), https://tc39.es/proposal-temporal/#sec-temporal-nudgetozonedtime
-ThrowCompletionOr<DurationNudgeResult> nudge_to_zoned_time(VM& vm, i8 sign, InternalDuration const& duration, ISODateTime const& iso_date_time, String const& time_zone, String const& calendar, u64 increment, Unit unit, RoundingMode rounding_mode)
+ThrowCompletionOr<DurationNudgeResult> nudge_to_zoned_time(VM& vm, i8 sign, InternalDuration const& duration, ISODateTime const& iso_date_time, Utf16View time_zone, Utf16View calendar, u64 increment, Unit unit, RoundingMode rounding_mode)
 {
     // 1. Let start be ? CalendarDateAdd(calendar, isoDateTime.[[ISODate]], duration.[[Date]], CONSTRAIN).
     auto start = TRY(calendar_date_add(vm, calendar, iso_date_time.iso_date, duration.date, Overflow::Constrain));
@@ -1298,7 +1298,7 @@ ThrowCompletionOr<DurationNudgeResult> nudge_to_day_or_time(VM& vm, InternalDura
 }
 
 // 7.5.37 BubbleRelativeDuration ( sign, duration, nudgedEpochNs, isoDateTime, timeZone, calendar, largestUnit, smallestUnit ), https://tc39.es/proposal-temporal/#sec-temporal-bubblerelativeduration
-ThrowCompletionOr<InternalDuration> bubble_relative_duration(VM& vm, i8 sign, InternalDuration duration, Crypto::SignedBigInteger const& nudged_epoch_ns, ISODateTime const& iso_date_time, Optional<String const&> time_zone, String const& calendar, Unit largest_unit, Unit smallest_unit)
+ThrowCompletionOr<InternalDuration> bubble_relative_duration(VM& vm, i8 sign, InternalDuration duration, Crypto::SignedBigInteger const& nudged_epoch_ns, ISODateTime const& iso_date_time, Optional<Utf16View> time_zone, Utf16View calendar, Unit largest_unit, Unit smallest_unit)
 {
     // 1. If smallestUnit is largestUnit, return duration.
     if (smallest_unit == largest_unit)
@@ -1399,7 +1399,7 @@ ThrowCompletionOr<InternalDuration> bubble_relative_duration(VM& vm, i8 sign, In
 }
 
 // 7.5.38 RoundRelativeDuration ( duration, originEpochNs, destEpochNs, isoDateTime, timeZone, calendar, largestUnit, increment, smallestUnit, roundingMode ), https://tc39.es/proposal-temporal/#sec-temporal-roundrelativeduration
-ThrowCompletionOr<InternalDuration> round_relative_duration(VM& vm, InternalDuration duration, Crypto::SignedBigInteger const& origin_epoch_ns, Crypto::SignedBigInteger const& dest_epoch_ns, ISODateTime const& iso_date_time, Optional<String const&> time_zone, String const& calendar, Unit largest_unit, u64 increment, Unit smallest_unit, RoundingMode rounding_mode)
+ThrowCompletionOr<InternalDuration> round_relative_duration(VM& vm, InternalDuration duration, Crypto::SignedBigInteger const& origin_epoch_ns, Crypto::SignedBigInteger const& dest_epoch_ns, ISODateTime const& iso_date_time, Optional<Utf16View> time_zone, Utf16View calendar, Unit largest_unit, u64 increment, Unit smallest_unit, RoundingMode rounding_mode)
 {
     // 1. Let irregularLengthUnit be false.
     auto irregular_length_unit = false;
@@ -1453,7 +1453,7 @@ ThrowCompletionOr<InternalDuration> round_relative_duration(VM& vm, InternalDura
 }
 
 // 7.5.39 TotalRelativeDuration ( duration, originEpochNs, destEpochNs, isoDateTime, timeZone, calendar, unit ), https://tc39.es/proposal-temporal/#sec-temporal-totalrelativeduration
-ThrowCompletionOr<Crypto::BigFraction> total_relative_duration(VM& vm, InternalDuration const& duration, Crypto::SignedBigInteger const& origin_epoch_ns, Crypto::SignedBigInteger const& dest_epoch_ns, ISODateTime const& iso_date_time, Optional<String const&> time_zone, String const& calendar, Unit unit)
+ThrowCompletionOr<Crypto::BigFraction> total_relative_duration(VM& vm, InternalDuration const& duration, Crypto::SignedBigInteger const& origin_epoch_ns, Crypto::SignedBigInteger const& dest_epoch_ns, ISODateTime const& iso_date_time, Optional<Utf16View> time_zone, Utf16View calendar, Unit unit)
 {
     // 1. If IsCalendarUnit(unit) is true, or timeZone is not UNSET and unit is DAY, then
     if (is_calendar_unit(unit) || (time_zone.has_value() && unit == Unit::Day)) {
@@ -1539,7 +1539,7 @@ Utf16String temporal_duration_to_string(Duration const& duration, Precision prec
         auto division_result = seconds_duration.divided_by(NANOSECONDS_PER_SECOND);
 
         // a. Let secondsPart be abs(truncate(secondsDuration / 10**9)) formatted as a decimal number.
-        auto seconds_part = MUST(division_result.quotient.unsigned_value().to_base(10));
+        auto seconds_part = MUST(division_result.quotient.unsigned_value().to_base_utf16(10));
 
         // b. Let subSecondsPart be FormatFractionalSeconds(abs(remainder(secondsDuration, 10**9)), precision).
         auto sub_seconds_part = format_fractional_seconds(division_result.remainder.unsigned_value().to_u64(), precision);
diff --git a/Libraries/LibJS/Runtime/Temporal/Duration.h b/Libraries/LibJS/Runtime/Temporal/Duration.h
index c10d64364c..145ebb7cdf 100644
--- a/Libraries/LibJS/Runtime/Temporal/Duration.h
+++ b/Libraries/LibJS/Runtime/Temporal/Duration.h
@@ -9,6 +9,7 @@
 #pragma once
 
 #include <AK/Optional.h>
+#include <AK/Utf16String.h>
 #include <LibCrypto/BigFraction/BigFraction.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/Object.h>
@@ -146,13 +147,13 @@ i8 time_duration_sign(TimeDuration const&);
 ThrowCompletionOr<double> date_duration_days(VM&, DateDuration const&, PlainDate const&);
 ThrowCompletionOr<TimeDuration> round_time_duration(VM&, TimeDuration const&, Crypto::UnsignedBigInteger const& increment, Unit, RoundingMode);
 Crypto::BigFraction total_time_duration(TimeDuration const&, Unit);
-ThrowCompletionOr<NudgeWindow> compute_nudge_window(VM&, i8 sign, InternalDuration const&, Crypto::SignedBigInteger const& origin_epoch_ns, ISODateTime const& iso_date_time, Optional<String const&> time_zone, String const& calendar, u64 increment, Unit, bool additional_shift);
-ThrowCompletionOr<CalendarNudgeResult> nudge_to_calendar_unit(VM&, i8 sign, InternalDuration const&, Crypto::SignedBigInteger const& origin_epoch_ns, Crypto::SignedBigInteger const& dest_epoch_ns, ISODateTime const&, Optional<String const&> time_zone, String const& calendar, u64 increment, Unit, RoundingMode);
-ThrowCompletionOr<DurationNudgeResult> nudge_to_zoned_time(VM&, i8 sign, InternalDuration const&, ISODateTime const&, String const& time_zone, String const& calendar, u64 increment, Unit, RoundingMode);
+ThrowCompletionOr<NudgeWindow> compute_nudge_window(VM&, i8 sign, InternalDuration const&, Crypto::SignedBigInteger const& origin_epoch_ns, ISODateTime const& iso_date_time, Optional<Utf16View> time_zone, Utf16View calendar, u64 increment, Unit, bool additional_shift);
+ThrowCompletionOr<CalendarNudgeResult> nudge_to_calendar_unit(VM&, i8 sign, InternalDuration const&, Crypto::SignedBigInteger const& origin_epoch_ns, Crypto::SignedBigInteger const& dest_epoch_ns, ISODateTime const&, Optional<Utf16View> time_zone, Utf16View calendar, u64 increment, Unit, RoundingMode);
+ThrowCompletionOr<DurationNudgeResult> nudge_to_zoned_time(VM&, i8 sign, InternalDuration const&, ISODateTime const&, Utf16View time_zone, Utf16View calendar, u64 increment, Unit, RoundingMode);
 ThrowCompletionOr<DurationNudgeResult> nudge_to_day_or_time(VM&, InternalDuration const&, Crypto::SignedBigInteger const& dest_epoch_ns, Unit largest_unit, u64 increment, Unit smallest_unit, RoundingMode);
-ThrowCompletionOr<InternalDuration> bubble_relative_duration(VM&, i8 sign, InternalDuration, Crypto::SignedBigInteger const& nudged_epoch_ns, ISODateTime const&, Optional<String const&> time_zone, String const& calendar, Unit largest_unit, Unit smallest_unit);
-ThrowCompletionOr<InternalDuration> round_relative_duration(VM&, InternalDuration, Crypto::SignedBigInteger const& origin_epoch_ns, Crypto::SignedBigInteger const& dest_epoch_ns, ISODateTime const&, Optional<String const&> time_zone, String const& calendar, Unit largest_unit, u64 increment, Unit smallest_unit, RoundingMode);
-ThrowCompletionOr<Crypto::BigFraction> total_relative_duration(VM&, InternalDuration const&, Crypto::SignedBigInteger const& origin_epoch_ns, Crypto::SignedBigInteger const& dest_epoch_ns, ISODateTime const&, Optional<String const&> time_zone, String const& calendar, Unit);
+ThrowCompletionOr<InternalDuration> bubble_relative_duration(VM&, i8 sign, InternalDuration, Crypto::SignedBigInteger const& nudged_epoch_ns, ISODateTime const&, Optional<Utf16View> time_zone, Utf16View calendar, Unit largest_unit, Unit smallest_unit);
+ThrowCompletionOr<InternalDuration> round_relative_duration(VM&, InternalDuration, Crypto::SignedBigInteger const& origin_epoch_ns, Crypto::SignedBigInteger const& dest_epoch_ns, ISODateTime const&, Optional<Utf16View> time_zone, Utf16View calendar, Unit largest_unit, u64 increment, Unit smallest_unit, RoundingMode);
+ThrowCompletionOr<Crypto::BigFraction> total_relative_duration(VM&, InternalDuration const&, Crypto::SignedBigInteger const& origin_epoch_ns, Crypto::SignedBigInteger const& dest_epoch_ns, ISODateTime const&, Optional<Utf16View> time_zone, Utf16View calendar, Unit);
 Utf16String temporal_duration_to_string(Duration const&, Precision);
 ThrowCompletionOr<GC::Ref<Duration>> add_durations(VM&, ArithmeticOperation, Duration const&, Value);
 
diff --git a/Libraries/LibJS/Runtime/Temporal/DurationPrototype.cpp b/Libraries/LibJS/Runtime/Temporal/DurationPrototype.cpp
index 98bbb9201c..d5cfb6982d 100644
--- a/Libraries/LibJS/Runtime/Temporal/DurationPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/DurationPrototype.cpp
@@ -34,7 +34,7 @@ void DurationPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 7.3.2 Temporal.Duration.prototype[ %Symbol.toStringTag% ], https://tc39.es/proposal-temporal/#sec-temporal.duration.prototype-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.Duration"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.Duration"_utf16_fly_string), Attribute::Configurable);
 
 #define __JS_ENUMERATE(unit) \
     define_native_accessor(realm, vm.names.unit, unit##_getter, {}, Attribute::Configurable);
diff --git a/Libraries/LibJS/Runtime/Temporal/ISORecords.h b/Libraries/LibJS/Runtime/Temporal/ISORecords.h
index d150ab90d2..33bf9783d4 100644
--- a/Libraries/LibJS/Runtime/Temporal/ISORecords.h
+++ b/Libraries/LibJS/Runtime/Temporal/ISORecords.h
@@ -57,7 +57,7 @@ struct ParsedISOTimeZone {
 
 // 13.33 Time Zone Identifier Parse Records, https://tc39.es/proposal-temporal/#sec-temporal-time-zone-identifier-parse-records
 struct ParsedTimeZoneIdentifier {
-    Optional<String> name;
+    Optional<Utf16String> name;
     Optional<i64> offset_minutes;
 };
 
diff --git a/Libraries/LibJS/Runtime/Temporal/Instant.cpp b/Libraries/LibJS/Runtime/Temporal/Instant.cpp
index d1ec919f3e..8ec1d8bedb 100644
--- a/Libraries/LibJS/Runtime/Temporal/Instant.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/Instant.cpp
@@ -200,11 +200,11 @@ Crypto::SignedBigInteger round_temporal_instant(Crypto::SignedBigInteger const&
 }
 
 // 8.5.8 TemporalInstantToString ( instant, timeZone, precision ), https://tc39.es/proposal-temporal/#sec-temporal-temporalinstanttostring
-String temporal_instant_to_string(Instant const& instant, Optional<String const&> time_zone, SecondsStringPrecision::Precision precision)
+Utf16String temporal_instant_to_string(Instant const& instant, Optional<Utf16View> time_zone, SecondsStringPrecision::Precision precision)
 {
     // 1. Let outputTimeZone be timeZone.
     // 2. If outputTimeZone is undefined, set outputTimeZone to "UTC".
-    auto const& output_time_zone = time_zone.value_or(UTC_TIME_ZONE);
+    auto output_time_zone = time_zone.value_or(UTC_TIME_ZONE);
 
     // 3. Let epochNs be instant.[[EpochNanoseconds]].
     auto const& epoch_nanoseconds = instant.epoch_nanoseconds()->big_integer();
@@ -215,12 +215,12 @@ String temporal_instant_to_string(Instant const& instant, Optional<String const&
     // 5. Let dateTimeString be ISODateTimeToString(isoDateTime, "iso8601", precision, NEVER).
     auto date_time_string = iso_date_time_to_string(iso_date_time, ISO8601_CALENDAR, precision, ShowCalendar::Never);
 
-    String time_zone_string;
+    Utf16String time_zone_string;
 
     // 6. If timeZone is undefined, then
     if (!time_zone.has_value()) {
         // a. Let timeZoneString be "Z".
-        time_zone_string = "Z"_string;
+        time_zone_string = "Z"_utf16_fly_string.to_utf16_string();
     }
     // 7. Else,
     else {
@@ -232,7 +232,7 @@ String temporal_instant_to_string(Instant const& instant, Optional<String const&
     }
 
     // 8. Return the string-concatenation of dateTimeString and timeZoneString.
-    return MUST(String::formatted("{}{}", date_time_string, time_zone_string));
+    return Utf16String::formatted("{}{}", date_time_string, time_zone_string);
 }
 
 // 8.5.9 DifferenceTemporalInstant ( operation, instant, other, options ), https://tc39.es/proposal-temporal/#sec-temporal-differencetemporalinstant
diff --git a/Libraries/LibJS/Runtime/Temporal/Instant.h b/Libraries/LibJS/Runtime/Temporal/Instant.h
index 48863676c8..0c7d0fefde 100644
--- a/Libraries/LibJS/Runtime/Temporal/Instant.h
+++ b/Libraries/LibJS/Runtime/Temporal/Instant.h
@@ -8,6 +8,7 @@
 
 #pragma once
 
+#include <AK/Utf16String.h>
 #include <LibCrypto/BigInt/SignedBigInteger.h>
 #include <LibCrypto/BigInt/UnsignedBigInteger.h>
 #include <LibJS/Runtime/BigInt.h>
@@ -63,7 +64,7 @@ i8 compare_epoch_nanoseconds(Crypto::SignedBigInteger const& epoch_nanoseconds_o
 ThrowCompletionOr<Crypto::SignedBigInteger> add_instant(VM&, Crypto::SignedBigInteger const& epoch_nanoseconds, TimeDuration const&);
 InternalDuration difference_instant(VM&, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, u64 rounding_increment, Unit smallest_unit, RoundingMode);
 Crypto::SignedBigInteger round_temporal_instant(Crypto::SignedBigInteger const& nanoseconds, u64 increment, Unit, RoundingMode);
-String temporal_instant_to_string(Instant const&, Optional<String const&> time_zone, SecondsStringPrecision::Precision);
+Utf16String temporal_instant_to_string(Instant const&, Optional<Utf16View> time_zone, SecondsStringPrecision::Precision);
 ThrowCompletionOr<GC::Ref<Duration>> difference_temporal_instant(VM&, DurationOperation, Instant const&, Value other, Value options);
 ThrowCompletionOr<GC::Ref<Instant>> add_duration_to_instant(VM&, ArithmeticOperation, Instant const&, Value temporal_duration_like);
 
diff --git a/Libraries/LibJS/Runtime/Temporal/InstantPrototype.cpp b/Libraries/LibJS/Runtime/Temporal/InstantPrototype.cpp
index 385ec35eb1..eff620d571 100644
--- a/Libraries/LibJS/Runtime/Temporal/InstantPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/InstantPrototype.cpp
@@ -31,7 +31,7 @@ void InstantPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 8.3.2 Temporal.Instant.prototype[ %Symbol.toStringTag% ], https://tc39.es/proposal-temporal/#sec-properties-of-the-temporal-instant-prototype-object
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.Instant"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.Instant"_utf16_fly_string), Attribute::Configurable);
 
     define_native_accessor(realm, vm.names.epochMilliseconds, epoch_milliseconds_getter, {}, Attribute::Configurable);
     define_native_accessor(realm, vm.names.epochNanoseconds, epoch_nanoseconds_getter, {}, Attribute::Configurable);
@@ -276,7 +276,7 @@ JS_DEFINE_NATIVE_FUNCTION(InstantPrototype::to_string)
     if (auto const* unit = smallest_unit.get_pointer<Unit>(); unit && *unit == Unit::Hour)
         return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, temporal_unit_to_string(*unit), vm.names.smallestUnit);
 
-    Optional<String> time_zone;
+    Optional<Utf16String> time_zone;
 
     // 11. If timeZone is not undefined, then
     if (!time_zone_value.is_undefined()) {
@@ -294,7 +294,7 @@ JS_DEFINE_NATIVE_FUNCTION(InstantPrototype::to_string)
     auto rounded_instant = MUST(create_temporal_instant(vm, BigInt::create(vm, move(rounded_nanoseconds))));
 
     // 15. Return TemporalInstantToString(roundedInstant, timeZone, precision.[[Precision]]).
-    return PrimitiveString::create(vm, temporal_instant_to_string(rounded_instant, time_zone, precision.precision));
+    return PrimitiveString::create(vm, temporal_instant_to_string(rounded_instant, time_zone.map([](auto const& time_zone) { return time_zone.utf16_view(); }), precision.precision));
 }
 
 // 8.3.12 Temporal.Instant.prototype.toLocaleString ( [ locales [ , options ] ] ), https://tc39.es/proposal-temporal/#sec-temporal.instant.prototype.tolocalestring
@@ -346,7 +346,7 @@ JS_DEFINE_NATIVE_FUNCTION(InstantPrototype::to_zoned_date_time_iso)
     auto time_zone = TRY(to_temporal_time_zone_identifier(vm, vm.argument(0)));
 
     // 4. Return ! CreateTemporalZonedDateTime(instant.[[EpochNanoseconds]], timeZone, "iso8601").
-    return MUST(create_temporal_zoned_date_time(vm, instant->epoch_nanoseconds(), move(time_zone), "iso8601"_string));
+    return MUST(create_temporal_zoned_date_time(vm, instant->epoch_nanoseconds(), move(time_zone), "iso8601"_utf16));
 }
 
 }
diff --git a/Libraries/LibJS/Runtime/Temporal/Now.cpp b/Libraries/LibJS/Runtime/Temporal/Now.cpp
index 54b0bc311b..da8989cdde 100644
--- a/Libraries/LibJS/Runtime/Temporal/Now.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/Now.cpp
@@ -31,7 +31,7 @@ void Now::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 2.1.1 Temporal.Now [ %Symbol.toStringTag% ], https://tc39.es/proposal-temporal/#sec-temporal-now-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.Now"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.Now"_utf16_fly_string), Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(realm, vm.names.timeZoneId, time_zone_id, 0, attr);
@@ -46,7 +46,8 @@ void Now::initialize(Realm& realm)
 JS_DEFINE_NATIVE_FUNCTION(Now::time_zone_id)
 {
     // 1. Return SystemTimeZoneIdentifier().
-    return PrimitiveString::create(vm, system_time_zone_identifier());
+    auto time_zone = system_time_zone_identifier();
+    return PrimitiveString::create(vm, time_zone);
 }
 
 // 2.2.2 Temporal.Now.instant ( ), https://tc39.es/proposal-temporal/#sec-temporal.now.instant
@@ -68,14 +69,14 @@ JS_DEFINE_NATIVE_FUNCTION(Now::plain_date_time_iso)
     auto iso_date_time = TRY(system_date_time(vm, temporal_time_zone_like));
 
     // 2. Return ! CreateTemporalDateTime(isoDateTime, "iso8601").
-    return MUST(create_temporal_date_time(vm, iso_date_time, "iso8601"_string));
+    return MUST(create_temporal_date_time(vm, iso_date_time, "iso8601"_utf16));
 }
 
 // 2.2.4 Temporal.Now.zonedDateTimeISO ( [ temporalTimeZoneLike ] ), https://tc39.es/proposal-temporal/#sec-temporal.now.zoneddatetimeiso
 JS_DEFINE_NATIVE_FUNCTION(Now::zoned_date_time_iso)
 {
     auto temporal_time_zone_like = vm.argument(0);
-    String time_zone;
+    Utf16String time_zone;
 
     // 1. If temporalTimeZoneLike is undefined, then
     if (temporal_time_zone_like.is_undefined()) {
@@ -92,7 +93,7 @@ JS_DEFINE_NATIVE_FUNCTION(Now::zoned_date_time_iso)
     auto nanoseconds = system_utc_epoch_nanoseconds(vm);
 
     //  4. Return ! CreateTemporalZonedDateTime(ns, timeZone, "iso8601").
-    return MUST(create_temporal_zoned_date_time(vm, BigInt::create(vm, move(nanoseconds)), move(time_zone), "iso8601"_string));
+    return MUST(create_temporal_zoned_date_time(vm, BigInt::create(vm, move(nanoseconds)), move(time_zone), "iso8601"_utf16));
 }
 
 // 2.2.5 Temporal.Now.plainDateISO ( [ temporalTimeZoneLike ] ), https://tc39.es/proposal-temporal/#sec-temporal.now.plaindateiso
@@ -104,7 +105,7 @@ JS_DEFINE_NATIVE_FUNCTION(Now::plain_date_iso)
     auto iso_date_time = TRY(system_date_time(vm, temporal_time_zone_like));
 
     // 2. Return ! CreateTemporalDate(isoDateTime.[[ISODate]], "iso8601").
-    return MUST(create_temporal_date(vm, iso_date_time.iso_date, "iso8601"_string));
+    return MUST(create_temporal_date(vm, iso_date_time.iso_date, "iso8601"_utf16));
 }
 
 // 2.2.6 Temporal.Now.plainTimeISO ( [ temporalTimeZoneLike ] ), https://tc39.es/proposal-temporal/#sec-temporal.now.plaintimeiso
@@ -148,7 +149,7 @@ Crypto::SignedBigInteger system_utc_epoch_nanoseconds(VM& vm)
 // 2.3.4 SystemDateTime ( temporalTimeZoneLike ), https://tc39.es/proposal-temporal/#sec-temporal-systemdatetime
 ThrowCompletionOr<ISODateTime> system_date_time(VM& vm, Value temporal_time_zone_like)
 {
-    String time_zone;
+    Utf16String time_zone;
 
     // 1. If temporalTimeZoneLike is undefined, then
     if (temporal_time_zone_like.is_undefined()) {
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainDate.cpp b/Libraries/LibJS/Runtime/Temporal/PlainDate.cpp
index 0d80e82183..d258caed39 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainDate.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainDate.cpp
@@ -26,7 +26,7 @@ namespace JS::Temporal {
 GC_DEFINE_ALLOCATOR(PlainDate);
 
 // 3 Temporal.PlainDate Objects, https://tc39.es/proposal-temporal/#sec-temporal-plaindate-objects
-PlainDate::PlainDate(ISODate iso_date, String calendar, Object& prototype)
+PlainDate::PlainDate(ISODate iso_date, Utf16String calendar, Object& prototype)
     : Object(ConstructWithPrototypeTag::Tag, prototype)
     , m_iso_date(iso_date)
     , m_calendar(move(calendar))
@@ -44,7 +44,7 @@ ISODate create_iso_date_record(double year, double month, double day)
 }
 
 // 3.5.3 CreateTemporalDate ( isoDate, calendar [ , newTarget ] ), https://tc39.es/proposal-temporal/#sec-temporal-createtemporaldate
-ThrowCompletionOr<GC::Ref<PlainDate>> create_temporal_date(VM& vm, ISODate iso_date, String calendar, GC::Ptr<FunctionObject> new_target)
+ThrowCompletionOr<GC::Ref<PlainDate>> create_temporal_date(VM& vm, ISODate iso_date, Utf16String calendar, GC::Ptr<FunctionObject> new_target)
 {
     auto& realm = *vm.current_realm();
 
@@ -141,7 +141,7 @@ ThrowCompletionOr<GC::Ref<PlainDate>> to_temporal_date(VM& vm, Value item, Value
     // 6. If calendar is empty, set calendar to "iso8601".
     auto calendar = result.calendar.has_value()
         ? TRY(canonicalize_calendar(vm, *result.calendar))
-        : TRY(canonicalize_calendar(vm, "iso8601"sv));
+        : TRY(canonicalize_calendar(vm, ISO8601_CALENDAR));
 
     // 8. Let resolvedOptions be ? GetOptionsObject(options).
     auto resolved_options = TRY(get_options_object(vm, options));
@@ -157,7 +157,7 @@ ThrowCompletionOr<GC::Ref<PlainDate>> to_temporal_date(VM& vm, Value item, Value
 }
 
 // 3.5.5 CompareSurpasses ( sign, year, monthOrCode, day, target ), https://tc39.es/proposal-temporal/#sec-temporal-comparesurpasses
-bool compare_surpasses(i8 sign, i32 year, Variant<u8, String> const& month_or_code, u8 day, CalendarDate const& target)
+bool compare_surpasses(i8 sign, i32 year, Variant<u8, Utf16String> const& month_or_code, u8 day, CalendarDate const& target)
 {
     // 1. If year ≠ target.[[Year]], then
     if (year != target.year) {
@@ -166,7 +166,7 @@ bool compare_surpasses(i8 sign, i32 year, Variant<u8, String> const& month_or_co
             return true;
     }
     // 2. Else if monthOrCode is a month code and monthOrCode is not target.[[MonthCode]], then
-    else if (auto const* month_code = month_or_code.get_pointer<String>(); month_code && *month_code != target.month_code) {
+    else if (auto const* month_code = month_or_code.get_pointer<Utf16String>(); month_code && *month_code != target.month_code) {
         // a. If sign > 0, then
         if (sign > 0) {
             // i. If monthOrCode is lexicographically greater than target.[[MonthCode]], return true.
@@ -312,22 +312,22 @@ ISODate add_days_to_iso_date(ISODate iso_date, double days)
 }
 
 // 3.5.9 PadISOYear ( y ), https://tc39.es/proposal-temporal/#sec-temporal-padisoyear
-String pad_iso_year(i32 year)
+Utf16String pad_iso_year(i32 year)
 {
     // 1. If y ≥ 0 and y ≤ 9999, return ToZeroPaddedDecimalString(y, 4).
     if (year >= 0 && year <= 9999)
-        return MUST(String::formatted("{:04}", year));
+        return Utf16String::formatted("{:04}", year);
 
     // 2. If y > 0, let yearSign be "+"; else, let yearSign be "-".
     auto year_sign = year > 0 ? '+' : '-';
 
     // 3. Let year be ToZeroPaddedDecimalString(abs(y), 6).
     // 4. Return the string-concatenation of yearSign and year.
-    return MUST(String::formatted("{}{:06}", year_sign, abs(year)));
+    return Utf16String::formatted("{}{:06}", year_sign, abs(year));
 }
 
 // 3.5.10 TemporalDateToString ( temporalDate, showCalendar ), https://tc39.es/proposal-temporal/#sec-temporal-temporaldatetostring
-String temporal_date_to_string(PlainDate const& temporal_date, ShowCalendar show_calendar)
+Utf16String temporal_date_to_string(PlainDate const& temporal_date, ShowCalendar show_calendar)
 {
     // 1. Let year be PadISOYear(temporalDate.[[ISODate]].[[Year]]).
     auto year = pad_iso_year(temporal_date.iso_date().year);
@@ -342,7 +342,7 @@ String temporal_date_to_string(PlainDate const& temporal_date, ShowCalendar show
     auto calendar = format_calendar_annotation(temporal_date.calendar(), show_calendar);
 
     // 5. Return the string-concatenation of year, the code unit 0x002D (HYPHEN-MINUS), month, the code unit 0x002D (HYPHEN-MINUS), day, and calendar.
-    return MUST(String::formatted("{}-{:02}-{:02}{}", year, month, day, calendar));
+    return Utf16String::formatted("{}-{:02}-{:02}{}", year, month, day, calendar);
 }
 
 // 3.5.11 ISODateWithinLimits ( isoDate ), https://tc39.es/proposal-temporal/#sec-temporal-isodatewithinlimits
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainDate.h b/Libraries/LibJS/Runtime/Temporal/PlainDate.h
index 397bc12d74..a60b2ad9f3 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainDate.h
+++ b/Libraries/LibJS/Runtime/Temporal/PlainDate.h
@@ -10,6 +10,7 @@
 #pragma once
 
 #include <AK/Types.h>
+#include <AK/Utf16String.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/Object.h>
 #include <LibJS/Runtime/Temporal/AbstractOperations.h>
@@ -26,25 +27,25 @@ public:
     virtual ~PlainDate() override = default;
 
     [[nodiscard]] ISODate iso_date() const { return m_iso_date; }
-    [[nodiscard]] String const& calendar() const { return m_calendar; }
+    [[nodiscard]] Utf16String const& calendar() const { return m_calendar; }
 
 private:
-    PlainDate(ISODate, String calendar, Object& prototype);
+    PlainDate(ISODate, Utf16String calendar, Object& prototype);
 
-    ISODate m_iso_date; // [[ISODate]]
-    String m_calendar;  // [[Calendar]]
+    ISODate m_iso_date;     // [[ISODate]]
+    Utf16String m_calendar; // [[Calendar]]
 };
 
 ISODate create_iso_date_record(double year, double month, double day);
 ThrowCompletionOr<GC::Ref<PlainDate>> to_temporal_date(VM& vm, Value item, Value options = js_undefined());
-ThrowCompletionOr<GC::Ref<PlainDate>> create_temporal_date(VM&, ISODate, String calendar, GC::Ptr<FunctionObject> new_target = {});
-bool compare_surpasses(i8 sign, i32 year, Variant<u8, String> const& month_or_code, u8 day, CalendarDate const& target);
+ThrowCompletionOr<GC::Ref<PlainDate>> create_temporal_date(VM&, ISODate, Utf16String calendar, GC::Ptr<FunctionObject> new_target = {});
+bool compare_surpasses(i8 sign, i32 year, Variant<u8, Utf16String> const& month_or_code, u8 day, CalendarDate const& target);
 bool iso_date_surpasses(VM&, i8 sign, ISODate base_date, ISODate iso_date2, double years, double months, double weeks, double days);
 ThrowCompletionOr<ISODate> regulate_iso_date(VM& vm, double year, double month, double day, Overflow overflow);
 bool is_valid_iso_date(double year, double month, double day);
 ISODate add_days_to_iso_date(ISODate, double days);
-String pad_iso_year(i32 year);
-String temporal_date_to_string(PlainDate const&, ShowCalendar);
+Utf16String pad_iso_year(i32 year);
+Utf16String temporal_date_to_string(PlainDate const&, ShowCalendar);
 bool iso_date_within_limits(ISODate);
 i8 compare_iso_date(ISODate, ISODate);
 ThrowCompletionOr<GC::Ref<Duration>> difference_temporal_plain_date(VM&, DurationOperation, PlainDate const&, Value other, Value options);
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainDateConstructor.cpp b/Libraries/LibJS/Runtime/Temporal/PlainDateConstructor.cpp
index 30998e8d5f..2b04a709ee 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainDateConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainDateConstructor.cpp
@@ -65,7 +65,7 @@ ThrowCompletionOr<GC::Ref<Object>> PlainDateConstructor::construct(FunctionObjec
 
     // 5. If calendar is undefined, set calendar to "iso8601".
     if (calendar_value.is_undefined())
-        calendar_value = PrimitiveString::create(vm, "iso8601"_string);
+        calendar_value = PrimitiveString::create(vm, "iso8601"_utf16_fly_string);
 
     // 6. If calendar is not a String, throw a TypeError exception.
     if (!calendar_value.is_string())
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp b/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp
index 4f09e9759b..a07223d3ed 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp
@@ -36,7 +36,7 @@ void PlainDatePrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 3.3.2 Temporal.PlainDate.prototype[ %Symbol.toStringTag% ], https://tc39.es/proposal-temporal/#sec-temporal.plaindate.prototype-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.PlainDate"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.PlainDate"_utf16_fly_string), Attribute::Configurable);
 
     define_native_accessor(realm, vm.names.calendarId, calendar_id_getter, {}, Attribute::Configurable);
     define_native_accessor(realm, vm.names.era, era_getter, {}, Attribute::Configurable);
@@ -161,8 +161,7 @@ JS_DEFINE_NATIVE_FUNCTION(PlainDatePrototype::month_code_getter)
     auto plain_date = TRY(typed_this_object(vm));
 
     // 3. Return CalendarISOToDate(plainDate.[[Calendar]], plainDate.[[ISODate]]).[[MonthCode]].
-    auto month_code = calendar_iso_to_date(plain_date->calendar(), plain_date->iso_date()).month_code;
-    return PrimitiveString::create(vm, move(month_code));
+    return PrimitiveString::create(vm, calendar_iso_to_date(plain_date->calendar(), plain_date->iso_date()).month_code);
 }
 
 // 3.3.12 get Temporal.PlainDate.prototype.weekOfYear, https://tc39.es/proposal-temporal/#sec-get-temporal.plaindate.prototype.weekofyear
@@ -398,7 +397,7 @@ JS_DEFINE_NATIVE_FUNCTION(PlainDatePrototype::to_zoned_date_time)
     // 2. Perform ? RequireInternalSlot(plainDate, [[InitializedTemporalDate]]).
     auto plain_date = TRY(typed_this_object(vm));
 
-    String time_zone;
+    Utf16String time_zone;
     Value temporal_time;
 
     // 3. If item is an Object, then
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainDateTime.cpp b/Libraries/LibJS/Runtime/Temporal/PlainDateTime.cpp
index ec13588dcf..3982a16b92 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainDateTime.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainDateTime.cpp
@@ -23,7 +23,7 @@ namespace JS::Temporal {
 
 GC_DEFINE_ALLOCATOR(PlainDateTime);
 
-PlainDateTime::PlainDateTime(ISODateTime const& iso_date_time, String calendar, Object& prototype)
+PlainDateTime::PlainDateTime(ISODateTime const& iso_date_time, Utf16String calendar, Object& prototype)
     : Object(ConstructWithPrototypeTag::Tag, prototype)
     , m_iso_date_time(iso_date_time)
     , m_calendar(move(calendar))
@@ -88,7 +88,7 @@ bool iso_date_time_within_limits(ISODateTime const& iso_date_time)
 }
 
 // 5.5.5 InterpretTemporalDateTimeFields ( calendar, fields, overflow ), https://tc39.es/proposal-temporal/#sec-temporal-interprettemporaldatetimefields
-ThrowCompletionOr<ISODateTime> interpret_temporal_date_time_fields(VM& vm, String const& calendar, CalendarFields& fields, Overflow overflow)
+ThrowCompletionOr<ISODateTime> interpret_temporal_date_time_fields(VM& vm, Utf16View calendar, CalendarFields& fields, Overflow overflow)
 {
     // 1. Let isoDate be ? CalendarDateFromFields(calendar, fields, overflow).
     auto iso_date = TRY(calendar_date_from_fields(vm, calendar, fields, overflow));
@@ -184,7 +184,7 @@ ThrowCompletionOr<GC::Ref<PlainDateTime>> to_temporal_date_time(VM& vm, Value it
     // 7. If calendar is empty, set calendar to "iso8601".
     auto calendar = result.calendar.has_value()
         ? TRY(canonicalize_calendar(vm, *result.calendar))
-        : TRY(canonicalize_calendar(vm, "iso8601"sv));
+        : TRY(canonicalize_calendar(vm, ISO8601_CALENDAR));
 
     // 9. Let resolvedOptions be ? GetOptionsObject(options).
     auto resolved_options = TRY(get_options_object(vm, options));
@@ -216,7 +216,7 @@ ISODateTime balance_iso_date_time(double year, double month, double day, double
 }
 
 // 5.5.8 CreateTemporalDateTime ( isoDateTime, calendar [ , newTarget ] ), https://tc39.es/proposal-temporal/#sec-temporal-createtemporaldatetime
-ThrowCompletionOr<GC::Ref<PlainDateTime>> create_temporal_date_time(VM& vm, ISODateTime const& iso_date_time, String calendar, GC::Ptr<FunctionObject> new_target)
+ThrowCompletionOr<GC::Ref<PlainDateTime>> create_temporal_date_time(VM& vm, ISODateTime const& iso_date_time, Utf16String calendar, GC::Ptr<FunctionObject> new_target)
 {
     auto& realm = *vm.current_realm();
 
@@ -238,7 +238,7 @@ ThrowCompletionOr<GC::Ref<PlainDateTime>> create_temporal_date_time(VM& vm, ISOD
 }
 
 // 5.5.9 ISODateTimeToString ( isoDateTime, calendar, precision, showCalendar ), https://tc39.es/proposal-temporal/#sec-temporal-isodatetimetostring
-String iso_date_time_to_string(ISODateTime const& iso_date_time, String const& calendar, SecondsStringPrecision::Precision precision, ShowCalendar show_calendar)
+Utf16String iso_date_time_to_string(ISODateTime const& iso_date_time, Utf16View calendar, SecondsStringPrecision::Precision precision, ShowCalendar show_calendar)
 {
     // 1. Let yearString be PadISOYear(isoDateTime.[[ISODate]].[[Year]]).
     auto year_string = pad_iso_year(iso_date_time.iso_date.year);
@@ -260,7 +260,7 @@ String iso_date_time_to_string(ISODateTime const& iso_date_time, String const& c
 
     // 7. Return the string-concatenation of yearString, the code unit 0x002D (HYPHEN-MINUS), monthString, the code unit 0x002D (HYPHEN-MINUS),
     //    dayString, 0x0054 (LATIN CAPITAL LETTER T), timeString, and calendarString.
-    return MUST(String::formatted("{}-{:02}-{:02}T{}{}", year_string, month, day, time_string, calendar_string));
+    return Utf16String::formatted("{}-{:02}-{:02}T{}{}", year_string, month, day, time_string, calendar_string);
 }
 
 // 5.5.10 CompareISODateTime ( isoDateTime1, isoDateTime2 ), https://tc39.es/proposal-temporal/#sec-temporal-compareisodatetime
@@ -294,7 +294,7 @@ ISODateTime round_iso_date_time(ISODateTime const& iso_date_time, u64 increment,
 }
 
 // 5.5.12 DifferenceISODateTime ( isoDateTime1, isoDateTime2, calendar, largestUnit ), https://tc39.es/proposal-temporal/#sec-temporal-differenceisodatetime
-InternalDuration difference_iso_date_time(VM& vm, ISODateTime const& iso_date_time1, ISODateTime const& iso_date_time2, String const& calendar, Unit largest_unit)
+InternalDuration difference_iso_date_time(VM& vm, ISODateTime const& iso_date_time1, ISODateTime const& iso_date_time2, Utf16View calendar, Unit largest_unit)
 {
     // 1. Assert: ISODateTimeWithinLimits(isoDateTime1) is true.
     VERIFY(iso_date_time_within_limits(iso_date_time1));
@@ -343,7 +343,7 @@ InternalDuration difference_iso_date_time(VM& vm, ISODateTime const& iso_date_ti
 }
 
 // 5.5.13 DifferencePlainDateTimeWithRounding ( isoDateTime1, isoDateTime2, calendar, largestUnit, roundingIncrement, smallestUnit, roundingMode ), https://tc39.es/proposal-temporal/#sec-temporal-differenceplaindatetimewithrounding
-ThrowCompletionOr<InternalDuration> difference_plain_date_time_with_rounding(VM& vm, ISODateTime const& iso_date_time1, ISODateTime const& iso_date_time2, String const& calendar, Unit largest_unit, u64 rounding_increment, Unit smallest_unit, RoundingMode rounding_mode)
+ThrowCompletionOr<InternalDuration> difference_plain_date_time_with_rounding(VM& vm, ISODateTime const& iso_date_time1, ISODateTime const& iso_date_time2, Utf16View calendar, Unit largest_unit, u64 rounding_increment, Unit smallest_unit, RoundingMode rounding_mode)
 {
     // 1. If CompareISODateTime(isoDateTime1, isoDateTime2) = 0, return CombineDateAndTimeDuration(ZeroDateDuration(), 0).
     if (compare_iso_date_time(iso_date_time1, iso_date_time2) == 0)
@@ -372,7 +372,7 @@ ThrowCompletionOr<InternalDuration> difference_plain_date_time_with_rounding(VM&
 }
 
 // 5.5.14 DifferencePlainDateTimeWithTotal ( isoDateTime1, isoDateTime2, calendar, unit ), https://tc39.es/proposal-temporal/#sec-temporal-differenceplaindatetimewithtotal
-ThrowCompletionOr<Crypto::BigFraction> difference_plain_date_time_with_total(VM& vm, ISODateTime const& iso_date_time1, ISODateTime const& iso_date_time2, String const& calendar, Unit unit)
+ThrowCompletionOr<Crypto::BigFraction> difference_plain_date_time_with_total(VM& vm, ISODateTime const& iso_date_time1, ISODateTime const& iso_date_time2, Utf16View calendar, Unit unit)
 {
     // 1. If CompareISODateTime(isoDateTime1, isoDateTime2) = 0, return 0.
     if (compare_iso_date_time(iso_date_time1, iso_date_time2) == 0)
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainDateTime.h b/Libraries/LibJS/Runtime/Temporal/PlainDateTime.h
index cdeec2d6e1..0c17870d8e 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainDateTime.h
+++ b/Libraries/LibJS/Runtime/Temporal/PlainDateTime.h
@@ -8,6 +8,7 @@
 
 #pragma once
 
+#include <AK/Utf16String.h>
 #include <LibCrypto/BigFraction/BigFraction.h>
 #include <LibJS/Runtime/Object.h>
 #include <LibJS/Runtime/Temporal/AbstractOperations.h>
@@ -23,28 +24,28 @@ public:
     virtual ~PlainDateTime() override = default;
 
     [[nodiscard]] ISODateTime iso_date_time() const { return m_iso_date_time; }
-    [[nodiscard]] String const& calendar() const { return m_calendar; }
+    [[nodiscard]] Utf16String const& calendar() const { return m_calendar; }
 
 private:
-    PlainDateTime(ISODateTime const&, String calendar, Object& prototype);
+    PlainDateTime(ISODateTime const&, Utf16String calendar, Object& prototype);
 
     ISODateTime m_iso_date_time; // [[ISODateTime]]
-    String m_calendar;           // [[Calendar]]
+    Utf16String m_calendar;      // [[Calendar]]
 };
 
 ISODateTime time_value_to_iso_date_time_record(double time_value);
 ISODateTime combine_iso_date_and_time_record(ISODate, Time const&);
 bool iso_date_time_within_limits(ISODateTime const&);
-ThrowCompletionOr<ISODateTime> interpret_temporal_date_time_fields(VM&, String const& calendar, CalendarFields&, Overflow);
+ThrowCompletionOr<ISODateTime> interpret_temporal_date_time_fields(VM&, Utf16View calendar, CalendarFields&, Overflow);
 ThrowCompletionOr<GC::Ref<PlainDateTime>> to_temporal_date_time(VM&, Value item, Value options = js_undefined());
 ISODateTime balance_iso_date_time(double year, double month, double day, double hour, double minute, double second, double millisecond, double microsecond, double nanosecond);
-ThrowCompletionOr<GC::Ref<PlainDateTime>> create_temporal_date_time(VM&, ISODateTime const&, String calendar, GC::Ptr<FunctionObject> new_target = {});
-String iso_date_time_to_string(ISODateTime const&, String const& calendar, SecondsStringPrecision::Precision, ShowCalendar);
+ThrowCompletionOr<GC::Ref<PlainDateTime>> create_temporal_date_time(VM&, ISODateTime const&, Utf16String calendar, GC::Ptr<FunctionObject> new_target = {});
+Utf16String iso_date_time_to_string(ISODateTime const&, Utf16View calendar, SecondsStringPrecision::Precision, ShowCalendar);
 i8 compare_iso_date_time(ISODateTime const&, ISODateTime const&);
 ISODateTime round_iso_date_time(ISODateTime const&, u64 increment, Unit, RoundingMode);
-InternalDuration difference_iso_date_time(VM&, ISODateTime const&, ISODateTime const&, String const& calendar, Unit largest_unit);
-ThrowCompletionOr<InternalDuration> difference_plain_date_time_with_rounding(VM&, ISODateTime const&, ISODateTime const&, String const& calendar, Unit largest_unit, u64 rounding_increment, Unit smallest_unit, RoundingMode);
-ThrowCompletionOr<Crypto::BigFraction> difference_plain_date_time_with_total(VM&, ISODateTime const&, ISODateTime const&, String const& calendar, Unit);
+InternalDuration difference_iso_date_time(VM&, ISODateTime const&, ISODateTime const&, Utf16View calendar, Unit largest_unit);
+ThrowCompletionOr<InternalDuration> difference_plain_date_time_with_rounding(VM&, ISODateTime const&, ISODateTime const&, Utf16View calendar, Unit largest_unit, u64 rounding_increment, Unit smallest_unit, RoundingMode);
+ThrowCompletionOr<Crypto::BigFraction> difference_plain_date_time_with_total(VM&, ISODateTime const&, ISODateTime const&, Utf16View calendar, Unit);
 ThrowCompletionOr<GC::Ref<Duration>> difference_temporal_plain_date_time(VM&, DurationOperation, PlainDateTime const&, Value other, Value options);
 ThrowCompletionOr<GC::Ref<PlainDateTime>> add_duration_to_date_time(VM&, ArithmeticOperation, PlainDateTime const&, Value temporal_duration_like, Value options);
 
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainDateTimeConstructor.cpp b/Libraries/LibJS/Runtime/Temporal/PlainDateTimeConstructor.cpp
index 7918c93904..12a6f7bb8c 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainDateTimeConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainDateTimeConstructor.cpp
@@ -94,7 +94,7 @@ ThrowCompletionOr<GC::Ref<Object>> PlainDateTimeConstructor::construct(FunctionO
 
     // 11. If calendar is undefined, set calendar to "iso8601".
     if (calendar_value.is_undefined())
-        calendar_value = PrimitiveString::create(vm, "iso8601"_string);
+        calendar_value = PrimitiveString::create(vm, "iso8601"_utf16_fly_string);
 
     // 12. If calendar is not a String, throw a TypeError exception.
     if (!calendar_value.is_string())
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainDateTimePrototype.cpp b/Libraries/LibJS/Runtime/Temporal/PlainDateTimePrototype.cpp
index 2f7cddbd3d..013b63e1d4 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainDateTimePrototype.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainDateTimePrototype.cpp
@@ -34,7 +34,7 @@ void PlainDateTimePrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 5.3.2 Temporal.PlainDateTime.prototype[ %Symbol.toStringTag% ], https://tc39.es/proposal-temporal/#sec-temporal.plaindatetime.prototype-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.PlainDateTime"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.PlainDateTime"_utf16_fly_string), Attribute::Configurable);
 
     define_native_accessor(realm, vm.names.calendarId, calendar_id_getter, {}, Attribute::Configurable);
     define_native_accessor(realm, vm.names.era, era_getter, {}, Attribute::Configurable);
@@ -166,8 +166,7 @@ JS_DEFINE_NATIVE_FUNCTION(PlainDateTimePrototype::month_code_getter)
     auto plain_date_time = TRY(typed_this_object(vm));
 
     // 3. Return CalendarISOToDate(plainDateTime.[[Calendar]], plainDateTime.[[ISODateTime]].[[ISODate]]).[[MonthCode]].
-    auto month_code = calendar_iso_to_date(plain_date_time->calendar(), plain_date_time->iso_date_time().iso_date).month_code;
-    return PrimitiveString::create(vm, move(month_code));
+    return PrimitiveString::create(vm, calendar_iso_to_date(plain_date_time->calendar(), plain_date_time->iso_date_time().iso_date).month_code);
 }
 
 // 5.3.10 get Temporal.PlainDateTime.prototype.hour, https://tc39.es/proposal-temporal/#sec-get-temporal.plaindatetime.prototype.hour
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainMonthDay.cpp b/Libraries/LibJS/Runtime/Temporal/PlainMonthDay.cpp
index 0349b07c35..fca6560742 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainMonthDay.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainMonthDay.cpp
@@ -19,7 +19,7 @@ namespace JS::Temporal {
 GC_DEFINE_ALLOCATOR(PlainMonthDay);
 
 // 10 Temporal.PlainMonthDay Objects, https://tc39.es/proposal-temporal/#sec-temporal-plainmonthday-objects
-PlainMonthDay::PlainMonthDay(ISODate iso_date, String calendar, Object& prototype)
+PlainMonthDay::PlainMonthDay(ISODate iso_date, Utf16String calendar, Object& prototype)
     : Object(ConstructWithPrototypeTag::Tag, prototype)
     , m_iso_date(iso_date)
     , m_calendar(move(calendar))
@@ -75,7 +75,7 @@ ThrowCompletionOr<GC::Ref<PlainMonthDay>> to_temporal_month_day(VM& vm, Value it
     // 6. If calendar is empty, set calendar to "iso8601".
     auto calendar = parse_result.calendar.has_value()
         ? TRY(canonicalize_calendar(vm, *parse_result.calendar))
-        : TRY(canonicalize_calendar(vm, "iso8601"sv));
+        : TRY(canonicalize_calendar(vm, ISO8601_CALENDAR));
 
     // 8. Let resolvedOptions be ? GetOptionsObject(options).
     auto resolved_options = TRY(get_options_object(vm, options));
@@ -115,7 +115,7 @@ ThrowCompletionOr<GC::Ref<PlainMonthDay>> to_temporal_month_day(VM& vm, Value it
 }
 
 // 10.5.2 CreateTemporalMonthDay ( isoDate, calendar [ , newTarget ] ), https://tc39.es/proposal-temporal/#sec-temporal-createtemporalmonthday
-ThrowCompletionOr<GC::Ref<PlainMonthDay>> create_temporal_month_day(VM& vm, ISODate iso_date, String calendar, GC::Ptr<FunctionObject> new_target)
+ThrowCompletionOr<GC::Ref<PlainMonthDay>> create_temporal_month_day(VM& vm, ISODate iso_date, Utf16String calendar, GC::Ptr<FunctionObject> new_target)
 {
     auto& realm = *vm.current_realm();
 
@@ -137,12 +137,12 @@ ThrowCompletionOr<GC::Ref<PlainMonthDay>> create_temporal_month_day(VM& vm, ISOD
 }
 
 // 10.5.3 TemporalMonthDayToString ( monthDay, showCalendar ), https://tc39.es/proposal-temporal/#sec-temporal-temporalmonthdaytostring
-String temporal_month_day_to_string(PlainMonthDay const& month_day, ShowCalendar show_calendar)
+Utf16String temporal_month_day_to_string(PlainMonthDay const& month_day, ShowCalendar show_calendar)
 {
     // 1. Let month be ToZeroPaddedDecimalString(monthDay.[[ISODate]].[[Month]], 2).
     // 2. Let day be ToZeroPaddedDecimalString(monthDay.[[ISODate]].[[Day]], 2).
     // 3. Let result be the string-concatenation of month, the code unit 0x002D (HYPHEN-MINUS), and day.
-    auto result = MUST(String::formatted("{:02}-{:02}", month_day.iso_date().month, month_day.iso_date().day));
+    auto result = Utf16String::formatted("{:02}-{:02}", month_day.iso_date().month, month_day.iso_date().day);
 
     // 4. If showCalendar is one of ALWAYS or CRITICAL, or monthDay.[[Calendar]] is not "iso8601", then
     if (show_calendar == ShowCalendar::Always || show_calendar == ShowCalendar::Critical || month_day.calendar() != ISO8601_CALENDAR) {
@@ -150,14 +150,14 @@ String temporal_month_day_to_string(PlainMonthDay const& month_day, ShowCalendar
         auto year = pad_iso_year(month_day.iso_date().year);
 
         // b. Set result to the string-concatenation of year, the code unit 0x002D (HYPHEN-MINUS), and result.
-        result = MUST(String::formatted("{}-{}", year, result));
+        result = Utf16String::formatted("{}-{}", year, result);
     }
 
     // 5. Let calendarString be FormatCalendarAnnotation(monthDay.[[Calendar]], showCalendar).
     auto calendar_string = format_calendar_annotation(month_day.calendar(), show_calendar);
 
     // 6. Set result to the string-concatenation of result and calendarString.
-    result = MUST(String::formatted("{}{}", result, calendar_string));
+    result = Utf16String::formatted("{}{}", result, calendar_string);
 
     // 7. Return result.
     return result;
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainMonthDay.h b/Libraries/LibJS/Runtime/Temporal/PlainMonthDay.h
index 0f2592240b..c19250880d 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainMonthDay.h
+++ b/Libraries/LibJS/Runtime/Temporal/PlainMonthDay.h
@@ -8,6 +8,7 @@
 #pragma once
 
 #include <AK/String.h>
+#include <AK/Utf16String.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/Object.h>
 #include <LibJS/Runtime/Temporal/AbstractOperations.h>
@@ -23,17 +24,17 @@ public:
     virtual ~PlainMonthDay() override = default;
 
     [[nodiscard]] ISODate iso_date() const { return m_iso_date; }
-    [[nodiscard]] String const& calendar() const { return m_calendar; }
+    [[nodiscard]] Utf16String const& calendar() const { return m_calendar; }
 
 private:
-    PlainMonthDay(ISODate, String calendar, Object& prototype);
+    PlainMonthDay(ISODate, Utf16String calendar, Object& prototype);
 
-    ISODate m_iso_date; // [[ISODate]]
-    String m_calendar;  // [[Calendar]]
+    ISODate m_iso_date;     // [[ISODate]]
+    Utf16String m_calendar; // [[Calendar]]
 };
 
 ThrowCompletionOr<GC::Ref<PlainMonthDay>> to_temporal_month_day(VM&, Value item, Value options = js_undefined());
-ThrowCompletionOr<GC::Ref<PlainMonthDay>> create_temporal_month_day(VM&, ISODate, String calendar, GC::Ptr<FunctionObject> new_target = {});
-String temporal_month_day_to_string(PlainMonthDay const&, ShowCalendar);
+ThrowCompletionOr<GC::Ref<PlainMonthDay>> create_temporal_month_day(VM&, ISODate, Utf16String calendar, GC::Ptr<FunctionObject> new_target = {});
+Utf16String temporal_month_day_to_string(PlainMonthDay const&, ShowCalendar);
 
 }
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainMonthDayConstructor.cpp b/Libraries/LibJS/Runtime/Temporal/PlainMonthDayConstructor.cpp
index 90f07add81..b090984829 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainMonthDayConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainMonthDayConstructor.cpp
@@ -69,7 +69,7 @@ ThrowCompletionOr<GC::Ref<Object>> PlainMonthDayConstructor::construct(FunctionO
 
     // 5. If calendar is undefined, set calendar to "iso8601".
     if (calendar_value.is_undefined())
-        calendar_value = PrimitiveString::create(vm, "iso8601"_string);
+        calendar_value = PrimitiveString::create(vm, "iso8601"_utf16_fly_string);
 
     // 6. If calendar is not a String, throw a TypeError exception.
     if (!calendar_value.is_string())
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainMonthDayPrototype.cpp b/Libraries/LibJS/Runtime/Temporal/PlainMonthDayPrototype.cpp
index 6e05ac1332..d40811ad0b 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainMonthDayPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainMonthDayPrototype.cpp
@@ -30,7 +30,7 @@ void PlainMonthDayPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 10.3.2 Temporal.PlainMonthDay.prototype[ %Symbol.toStringTag% ], https://tc39.es/proposal-temporal/#sec-temporal.plainmonthday.prototype-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.PlainMonthDay"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.PlainMonthDay"_utf16_fly_string), Attribute::Configurable);
 
     define_native_accessor(realm, vm.names.calendarId, calendar_id_getter, {}, Attribute::Configurable);
     define_native_accessor(realm, vm.names.monthCode, month_code_getter, {}, Attribute::Configurable);
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainTime.h b/Libraries/LibJS/Runtime/Temporal/PlainTime.h
index e5e36d8927..735fb6c294 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainTime.h
+++ b/Libraries/LibJS/Runtime/Temporal/PlainTime.h
@@ -8,6 +8,7 @@
 
 #pragma once
 
+#include <AK/Utf16String.h>
 #include <LibJS/Runtime/Temporal/AbstractOperations.h>
 #include <LibJS/Runtime/Temporal/ISORecords.h>
 
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainTimePrototype.cpp b/Libraries/LibJS/Runtime/Temporal/PlainTimePrototype.cpp
index 0aa953fc3c..7b5fcdf183 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainTimePrototype.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainTimePrototype.cpp
@@ -28,7 +28,7 @@ void PlainTimePrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 4.3.2 Temporal.PlainTime.prototype[ %Symbol.toStringTag% ], https://tc39.es/proposal-temporal/#sec-temporal.plaintime.prototype-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.PlainTime"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.PlainTime"_utf16_fly_string), Attribute::Configurable);
 
     define_native_accessor(realm, vm.names.hour, hour_getter, {}, Attribute::Configurable);
     define_native_accessor(realm, vm.names.minute, minute_getter, {}, Attribute::Configurable);
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.cpp b/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.cpp
index fc97e57fd7..e662e08ae4 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.cpp
@@ -22,7 +22,7 @@ namespace JS::Temporal {
 GC_DEFINE_ALLOCATOR(PlainYearMonth);
 
 // 9 Temporal.PlainYearMonth Objects, https://tc39.es/proposal-temporal/#sec-temporal-plainyearmonth-objects
-PlainYearMonth::PlainYearMonth(ISODate iso_date, String calendar, Object& prototype)
+PlainYearMonth::PlainYearMonth(ISODate iso_date, Utf16String calendar, Object& prototype)
     : Object(ConstructWithPrototypeTag::Tag, prototype)
     , m_iso_date(iso_date)
     , m_calendar(move(calendar))
@@ -78,7 +78,7 @@ ThrowCompletionOr<GC::Ref<PlainYearMonth>> to_temporal_year_month(VM& vm, Value
     // 6. If calendar is empty, set calendar to "iso8601".
     auto calendar = parse_result.calendar.has_value()
         ? TRY(canonicalize_calendar(vm, *parse_result.calendar))
-        : TRY(canonicalize_calendar(vm, "iso8601"sv));
+        : TRY(canonicalize_calendar(vm, ISO8601_CALENDAR));
 
     // 8. Let resolvedOptions be ? GetOptionsObject(options).
     auto resolved_options = TRY(get_options_object(vm, options));
@@ -138,7 +138,7 @@ ISOYearMonth balance_iso_year_month(double year, double month)
 }
 
 // 9.5.5 CreateTemporalYearMonth ( isoDate, calendar [ , newTarget ] ), https://tc39.es/proposal-temporal/#sec-temporal-createtemporalyearmonth
-ThrowCompletionOr<GC::Ref<PlainYearMonth>> create_temporal_year_month(VM& vm, ISODate iso_date, String calendar, GC::Ptr<FunctionObject> new_target)
+ThrowCompletionOr<GC::Ref<PlainYearMonth>> create_temporal_year_month(VM& vm, ISODate iso_date, Utf16String calendar, GC::Ptr<FunctionObject> new_target)
 {
     auto& realm = *vm.current_realm();
 
@@ -160,27 +160,27 @@ ThrowCompletionOr<GC::Ref<PlainYearMonth>> create_temporal_year_month(VM& vm, IS
 }
 
 // 9.5.6 TemporalYearMonthToString ( yearMonth, showCalendar ), https://tc39.es/proposal-temporal/#sec-temporal-temporalyearmonthtostring
-String temporal_year_month_to_string(PlainYearMonth const& year_month, ShowCalendar show_calendar)
+Utf16String temporal_year_month_to_string(PlainYearMonth const& year_month, ShowCalendar show_calendar)
 {
     // 1. Let year be PadISOYear(yearMonth.[[ISODate]].[[Year]]).
     auto year = pad_iso_year(year_month.iso_date().year);
 
     // 2. Let month be ToZeroPaddedDecimalString(yearMonth.[[ISODate]].[[Month]], 2).
     // 3. Let result be the string-concatenation of year, the code unit 0x002D (HYPHEN-MINUS), and month.
-    auto result = MUST(String::formatted("{}-{:02}", year, year_month.iso_date().month));
+    auto result = Utf16String::formatted("{}-{:02}", year, year_month.iso_date().month);
 
     // 4. If showCalendar is one of always or critical, or yearMonth.[[Calendar]] is not "iso8601", then
     if (show_calendar == ShowCalendar::Always || show_calendar == ShowCalendar::Critical || year_month.calendar() != ISO8601_CALENDAR) {
         // a. Let day be ToZeroPaddedDecimalString(yearMonth.[[ISODate]].[[Day]], 2).
         // b. Set result to the string-concatenation of result, the code unit 0x002D (HYPHEN-MINUS), and day.
-        result = MUST(String::formatted("{}-{:02}", result, year_month.iso_date().day));
+        result = Utf16String::formatted("{}-{:02}", result, year_month.iso_date().day);
     }
 
     // 5. Let calendarString be FormatCalendarAnnotation(yearMonth.[[Calendar]], showCalendar).
     auto calendar_string = format_calendar_annotation(year_month.calendar(), show_calendar);
 
     // 6. Set result to the string-concatenation of result and calendarString.
-    result = MUST(String::formatted("{}{}", result, calendar_string));
+    result = Utf16String::formatted("{}{}", result, calendar_string);
 
     // 7. Return result.
     return result;
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.h b/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.h
index fe54d60b66..226e1ed293 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.h
+++ b/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.h
@@ -8,6 +8,7 @@
 #pragma once
 
 #include <AK/String.h>
+#include <AK/Utf16String.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/Object.h>
 #include <LibJS/Runtime/Temporal/AbstractOperations.h>
@@ -24,20 +25,20 @@ public:
     virtual ~PlainYearMonth() override = default;
 
     [[nodiscard]] ISODate iso_date() const { return m_iso_date; }
-    [[nodiscard]] String const& calendar() const { return m_calendar; }
+    [[nodiscard]] Utf16String const& calendar() const { return m_calendar; }
 
 private:
-    PlainYearMonth(ISODate, String calendar, Object& prototype);
+    PlainYearMonth(ISODate, Utf16String calendar, Object& prototype);
 
-    ISODate m_iso_date; // [[ISODate]]
-    String m_calendar;  // [[Calendar]]
+    ISODate m_iso_date;     // [[ISODate]]
+    Utf16String m_calendar; // [[Calendar]]
 };
 
 ThrowCompletionOr<GC::Ref<PlainYearMonth>> to_temporal_year_month(VM&, Value item, Value options = js_undefined());
 bool iso_year_month_within_limits(ISODate);
 ISOYearMonth balance_iso_year_month(double year, double month);
-ThrowCompletionOr<GC::Ref<PlainYearMonth>> create_temporal_year_month(VM&, ISODate, String calendar, GC::Ptr<FunctionObject> new_target = {});
-String temporal_year_month_to_string(PlainYearMonth const&, ShowCalendar);
+ThrowCompletionOr<GC::Ref<PlainYearMonth>> create_temporal_year_month(VM&, ISODate, Utf16String calendar, GC::Ptr<FunctionObject> new_target = {});
+Utf16String temporal_year_month_to_string(PlainYearMonth const&, ShowCalendar);
 ThrowCompletionOr<GC::Ref<Duration>> difference_temporal_plain_year_month(VM&, DurationOperation, PlainYearMonth const&, Value other, Value options);
 ThrowCompletionOr<GC::Ref<PlainYearMonth>> add_duration_to_year_month(VM&, ArithmeticOperation, PlainYearMonth const&, Value temporal_duration_like, Value options);
 
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainYearMonthConstructor.cpp b/Libraries/LibJS/Runtime/Temporal/PlainYearMonthConstructor.cpp
index 064301f0e3..10e6e1e60c 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainYearMonthConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainYearMonthConstructor.cpp
@@ -69,7 +69,7 @@ ThrowCompletionOr<GC::Ref<Object>> PlainYearMonthConstructor::construct(Function
 
     // 5. If calendar is undefined, set calendar to "iso8601".
     if (calendar_value.is_undefined())
-        calendar_value = PrimitiveString::create(vm, "iso8601"_string);
+        calendar_value = PrimitiveString::create(vm, "iso8601"_utf16_fly_string);
 
     // 6. If calendar is not a String, throw a TypeError exception.
     if (!calendar_value.is_string())
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.cpp b/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.cpp
index 3f414845ea..aaebd4b5b9 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.cpp
@@ -30,7 +30,7 @@ void PlainYearMonthPrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 9.3.2 Temporal.PlainYearMonth.prototype[ %Symbol.toStringTag% ], https://tc39.es/proposal-temporal/#sec-temporal.plainyearmonth.prototype-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.PlainYearMonth"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.PlainYearMonth"_utf16_fly_string), Attribute::Configurable);
 
     define_native_accessor(realm, vm.names.calendarId, calendar_id_getter, {}, Attribute::Configurable);
     define_native_accessor(realm, vm.names.era, era_getter, {}, Attribute::Configurable);
@@ -137,8 +137,7 @@ JS_DEFINE_NATIVE_FUNCTION(PlainYearMonthPrototype::month_code_getter)
     auto plain_year_month = TRY(typed_this_object(vm));
 
     // 3. Return CalendarISOToDate(plainYearMonth.[[Calendar]], plainYearMonth.[[ISODate]]).[[MonthCode]].
-    auto month_code = calendar_iso_to_date(plain_year_month->calendar(), plain_year_month->iso_date()).month_code;
-    return PrimitiveString::create(vm, move(month_code));
+    return PrimitiveString::create(vm, calendar_iso_to_date(plain_year_month->calendar(), plain_year_month->iso_date()).month_code);
 }
 
 // 9.3.13 Temporal.PlainYearMonth.prototype.with ( temporalYearMonthLike [ , options ] ), https://tc39.es/proposal-temporal/#sec-temporal.plainyearmonth.prototype.with
diff --git a/Libraries/LibJS/Runtime/Temporal/Temporal.cpp b/Libraries/LibJS/Runtime/Temporal/Temporal.cpp
index 85e93573ea..a371451429 100644
--- a/Libraries/LibJS/Runtime/Temporal/Temporal.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/Temporal.cpp
@@ -34,7 +34,7 @@ void Temporal::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 1.1.1 Temporal [ %Symbol.toStringTag% ], https://tc39.es/proposal-temporal/#sec-temporal-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal"_utf16_fly_string), Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_direct_property(vm.names.Now, realm.create<Now>(realm), attr);
diff --git a/Libraries/LibJS/Runtime/Temporal/TimeZone.cpp b/Libraries/LibJS/Runtime/Temporal/TimeZone.cpp
index ae3b8151c4..0bf637a09b 100644
--- a/Libraries/LibJS/Runtime/Temporal/TimeZone.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/TimeZone.cpp
@@ -26,7 +26,7 @@
 
 namespace JS::Temporal {
 
-String UTC_TIME_ZONE = "UTC"_string;
+Utf16String UTC_TIME_ZONE = "UTC"_utf16;
 
 // 11.1.2 GetISOPartsFromEpoch ( epochNanoseconds ), https://tc39.es/proposal-temporal/#sec-temporal-getisopartsfromepoch
 ISODateTime get_iso_parts_from_epoch(Crypto::SignedBigInteger const& epoch_nanoseconds)
@@ -82,7 +82,7 @@ ISODateTime get_iso_parts_from_epoch(Crypto::SignedBigInteger const& epoch_nanos
 }
 
 // 11.1.3 GetNamedTimeZoneNextTransition ( timeZoneIdentifier, epochNanoseconds ), https://tc39.es/proposal-temporal/#sec-temporal-getnamedtimezonenexttransition
-Optional<Crypto::SignedBigInteger> get_named_time_zone_next_transition(String const& time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds)
+Optional<Crypto::SignedBigInteger> get_named_time_zone_next_transition(Utf16View time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds)
 {
     auto epoch_milliseconds = big_floor(epoch_nanoseconds, NANOSECONDS_PER_MILLISECOND);
     auto time = UnixDateTime::from_milliseconds_since_epoch(clip_bigint_to_sane_time(epoch_milliseconds));
@@ -92,7 +92,7 @@ Optional<Crypto::SignedBigInteger> get_named_time_zone_next_transition(String co
         .include_given_time = Unicode::TimeZoneTransition::Options::IncludeGivenTime::No,
         .transition_rule = Unicode::TimeZoneTransition::Options::TransitionRule::TransitionWhereUTCOffsetChanges,
     };
-    auto time_zone_transition = Unicode::get_time_zone_transition(time_zone, time, options);
+    auto time_zone_transition = Unicode::get_time_zone_transition(time_zone.bytes(), time, options);
 
     if (!time_zone_transition.has_value())
         return {};
@@ -105,7 +105,7 @@ Optional<Crypto::SignedBigInteger> get_named_time_zone_next_transition(String co
 }
 
 // 11.1.4 GetNamedTimeZonePreviousTransition ( timeZoneIdentifier, epochNanoseconds ), https://tc39.es/proposal-temporal/#sec-temporal-getnamedtimezoneprevioustransition
-Optional<Crypto::SignedBigInteger> get_named_time_zone_previous_transition(String const& time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds)
+Optional<Crypto::SignedBigInteger> get_named_time_zone_previous_transition(Utf16View time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds)
 {
     auto epoch_milliseconds = big_floor(epoch_nanoseconds, NANOSECONDS_PER_MILLISECOND);
     auto time = UnixDateTime::from_milliseconds_since_epoch(clip_bigint_to_sane_time(epoch_milliseconds));
@@ -122,7 +122,7 @@ Optional<Crypto::SignedBigInteger> get_named_time_zone_previous_transition(Strin
         .include_given_time = has_sub_millisecond_precision ? Unicode::TimeZoneTransition::Options::IncludeGivenTime::Yes : Unicode::TimeZoneTransition::Options::IncludeGivenTime::No,
         .transition_rule = Unicode::TimeZoneTransition::Options::TransitionRule::TransitionWhereUTCOffsetChanges,
     };
-    auto time_zone_transition = Unicode::get_time_zone_transition(time_zone, time, options);
+    auto time_zone_transition = Unicode::get_time_zone_transition(time_zone.bytes(), time, options);
 
     if (!time_zone_transition.has_value())
         return {};
@@ -135,7 +135,7 @@ Optional<Crypto::SignedBigInteger> get_named_time_zone_previous_transition(Strin
 }
 
 // 11.1.5 FormatOffsetTimeZoneIdentifier ( offsetMinutes [ , style ] ), https://tc39.es/proposal-temporal/#sec-temporal-formatoffsettimezoneidentifier
-String format_offset_time_zone_identifier(i64 offset_minutes, Optional<TimeStyle> style)
+Utf16String format_offset_time_zone_identifier(i64 offset_minutes, Optional<TimeStyle> style)
 {
     // 1. If offsetMinutes ≥ 0, let sign be the code unit 0x002B (PLUS SIGN); else, let sign be the code unit 0x002D (HYPHEN-MINUS).
     auto sign = offset_minutes >= 0 ? '+' : '-';
@@ -153,11 +153,11 @@ String format_offset_time_zone_identifier(i64 offset_minutes, Optional<TimeStyle
     auto time_string = format_time_string(hour, minute, 0, 0, SecondsStringPrecision::Minute {}, style);
 
     // 6. Return the string-concatenation of sign and timeString.
-    return MUST(String::formatted("{}{}", sign, time_string));
+    return Utf16String::formatted("{}{}", sign, time_string);
 }
 
 // 11.1.6 FormatUTCOffsetNanoseconds ( offsetNanoseconds ), https://tc39.es/proposal-temporal/#sec-temporal-formatutcoffsetnanoseconds
-String format_utc_offset_nanoseconds(i64 offset_nanoseconds)
+Utf16String format_utc_offset_nanoseconds(i64 offset_nanoseconds)
 {
     // 1. If offsetNanoseconds ≥ 0, let sign be the code unit 0x002B (PLUS SIGN); else, let sign be the code unit 0x002D (HYPHEN-MINUS).
     auto sign = offset_nanoseconds >= 0 ? '+' : '-';
@@ -186,11 +186,11 @@ String format_utc_offset_nanoseconds(i64 offset_nanoseconds)
     auto time_string = format_time_string(hour, minute, second, sub_second_nanoseconds, precision);
 
     // 9. Return the string-concatenation of sign and timeString.
-    return MUST(String::formatted("{}{}", sign, time_string));
+    return Utf16String::formatted("{}{}", sign, time_string);
 }
 
 // 11.1.7 FormatDateTimeUTCOffsetRounded ( offsetNanoseconds ), https://tc39.es/proposal-temporal/#sec-temporal-formatdatetimeutcoffsetrounded
-String format_date_time_utc_offset_rounded(i64 offset_nanoseconds)
+Utf16String format_date_time_utc_offset_rounded(i64 offset_nanoseconds)
 {
     // 1. Set offsetNanoseconds to RoundNumberToIncrement(offsetNanoseconds, 60 × 10**9, HALF-EXPAND).
     auto offset_nanoseconds_value = round_number_to_increment(static_cast<double>(offset_nanoseconds), 60'000'000'000, RoundingMode::HalfExpand);
@@ -202,11 +202,11 @@ String format_date_time_utc_offset_rounded(i64 offset_nanoseconds)
     VERIFY(trunc(offset_minutes) == offset_minutes);
 
     // 4. Return FormatOffsetTimeZoneIdentifier(offsetMinutes).
-    return format_offset_time_zone_identifier(static_cast<i64>(offset_minutes));
+    return format_utc_offset_nanoseconds(static_cast<i64>(offset_minutes) * 60'000'000'000);
 }
 
 // 11.1.8 ToTemporalTimeZoneIdentifier ( temporalTimeZoneLike ), https://tc39.es/proposal-temporal/#sec-temporal-totemporaltimezoneidentifier
-ThrowCompletionOr<String> to_temporal_time_zone_identifier(VM& vm, Value temporal_time_zone_like)
+ThrowCompletionOr<Utf16String> to_temporal_time_zone_identifier(VM& vm, Value temporal_time_zone_like)
 {
     // 1. If temporalTimeZoneLike is an Object and temporalTimeZoneLike has an [[InitializedTemporalZonedDateTime]]
     //    internal slot, return temporalTimeZoneLike.[[TimeZone]].
@@ -221,7 +221,7 @@ ThrowCompletionOr<String> to_temporal_time_zone_identifier(VM& vm, Value tempora
 }
 
 // 11.1.8 ToTemporalTimeZoneIdentifier ( temporalTimeZoneLike ), https://tc39.es/proposal-temporal/#sec-temporal-totemporaltimezoneidentifier
-ThrowCompletionOr<String> to_temporal_time_zone_identifier(VM& vm, Utf16View temporal_time_zone_like)
+ThrowCompletionOr<Utf16String> to_temporal_time_zone_identifier(VM& vm, Utf16View temporal_time_zone_like)
 {
     // 3. Let parseResult be ? ParseTemporalTimeZoneString(temporalTimeZoneLike).
     auto parse_result = TRY(parse_temporal_time_zone_string(vm, temporal_time_zone_like));
@@ -244,7 +244,7 @@ ThrowCompletionOr<String> to_temporal_time_zone_identifier(VM& vm, Utf16View tem
 }
 
 // 11.1.9 GetOffsetNanosecondsFor ( timeZone, epochNs ), https://tc39.es/proposal-temporal/#sec-temporal-getoffsetnanosecondsfor
-i64 get_offset_nanoseconds_for(String const& time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds)
+i64 get_offset_nanoseconds_for(Utf16View time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds)
 {
     // 1. Let parseResult be ! ParseTimeZoneIdentifier(timeZone).
     auto const& parse_result = parse_time_zone_identifier(time_zone);
@@ -254,11 +254,11 @@ i64 get_offset_nanoseconds_for(String const& time_zone, Crypto::SignedBigInteger
         return *parse_result.offset_minutes * 60'000'000'000;
 
     // 3. Return GetNamedTimeZoneOffsetNanoseconds(parseResult.[[Name]], epochNs).
-    return get_named_time_zone_offset_nanoseconds(*parse_result.name, epoch_nanoseconds).offset.to_nanoseconds();
+    return get_named_time_zone_offset_nanoseconds(parse_result.name->utf16_view().bytes(), epoch_nanoseconds).offset.to_nanoseconds();
 }
 
 // 11.1.10 GetISODateTimeFor ( timeZone, epochNs ), https://tc39.es/proposal-temporal/#sec-temporal-getisodatetimefor
-ISODateTime get_iso_date_time_for(String const& time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds)
+ISODateTime get_iso_date_time_for(Utf16View time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds)
 {
     // 1. Let offsetNanoseconds be GetOffsetNanosecondsFor(timeZone, epochNs).
     auto offset_nanoseconds = get_offset_nanoseconds_for(time_zone, epoch_nanoseconds);
@@ -271,7 +271,7 @@ ISODateTime get_iso_date_time_for(String const& time_zone, Crypto::SignedBigInte
 }
 
 // 11.1.11 GetEpochNanosecondsFor ( timeZone, isoDateTime, disambiguation ), https://tc39.es/proposal-temporal/#sec-temporal-getepochnanosecondsfor
-ThrowCompletionOr<Crypto::SignedBigInteger> get_epoch_nanoseconds_for(VM& vm, String const& time_zone, ISODateTime const& iso_date_time, Disambiguation disambiguation)
+ThrowCompletionOr<Crypto::SignedBigInteger> get_epoch_nanoseconds_for(VM& vm, Utf16View time_zone, ISODateTime const& iso_date_time, Disambiguation disambiguation)
 {
     // 1. Let possibleEpochNs be ? GetPossibleEpochNanoseconds(timeZone, isoDateTime).
     auto possible_epoch_ns = TRY(get_possible_epoch_nanoseconds(vm, time_zone, iso_date_time));
@@ -281,7 +281,7 @@ ThrowCompletionOr<Crypto::SignedBigInteger> get_epoch_nanoseconds_for(VM& vm, St
 }
 
 // 11.1.12 DisambiguatePossibleEpochNanoseconds ( possibleEpochNs, timeZone, isoDateTime, disambiguation ), https://tc39.es/proposal-temporal/#sec-temporal-disambiguatepossibleepochnanoseconds
-ThrowCompletionOr<Crypto::SignedBigInteger> disambiguate_possible_epoch_nanoseconds(VM& vm, Vector<Crypto::SignedBigInteger> possible_epoch_ns, String const& time_zone, ISODateTime const& iso_date_time, Disambiguation disambiguation)
+ThrowCompletionOr<Crypto::SignedBigInteger> disambiguate_possible_epoch_nanoseconds(VM& vm, Vector<Crypto::SignedBigInteger> possible_epoch_ns, Utf16View time_zone, ISODateTime const& iso_date_time, Disambiguation disambiguation)
 {
     // 1. Let n be the number of elements in possibleEpochNs.
     auto n = possible_epoch_ns.size();
@@ -392,7 +392,7 @@ ThrowCompletionOr<Crypto::SignedBigInteger> disambiguate_possible_epoch_nanoseco
 }
 
 // 11.1.13 GetPossibleEpochNanoseconds ( timeZone, isoDateTime ), https://tc39.es/proposal-temporal/#sec-temporal-getpossibleepochnanoseconds
-ThrowCompletionOr<Vector<Crypto::SignedBigInteger>> get_possible_epoch_nanoseconds(VM& vm, String const& time_zone, ISODateTime const& iso_date_time)
+ThrowCompletionOr<Vector<Crypto::SignedBigInteger>> get_possible_epoch_nanoseconds(VM& vm, Utf16View time_zone, ISODateTime const& iso_date_time)
 {
     Vector<Crypto::SignedBigInteger> possible_epoch_nanoseconds;
 
@@ -425,7 +425,7 @@ ThrowCompletionOr<Vector<Crypto::SignedBigInteger>> get_possible_epoch_nanosecon
     // 3. Else,
     else {
         // a. Let possibleEpochNanoseconds be GetNamedTimeZoneEpochNanoseconds(parseResult.[[Name]], isoDateTime).
-        possible_epoch_nanoseconds = get_named_time_zone_epoch_nanoseconds(*parse_result.name, iso_date_time);
+        possible_epoch_nanoseconds = get_named_time_zone_epoch_nanoseconds(parse_result.name->utf16_view().bytes(), iso_date_time);
     }
 
     // 4. For each value epochNanoseconds in possibleEpochNanoseconds, do
@@ -440,7 +440,7 @@ ThrowCompletionOr<Vector<Crypto::SignedBigInteger>> get_possible_epoch_nanosecon
 }
 
 // 11.1.14 GetStartOfDay ( timeZone, isoDate ), https://tc39.es/proposal-temporal/#sec-temporal-getstartofday
-ThrowCompletionOr<Crypto::SignedBigInteger> get_start_of_day(VM& vm, String const& time_zone, ISODate iso_date)
+ThrowCompletionOr<Crypto::SignedBigInteger> get_start_of_day(VM& vm, Utf16View time_zone, ISODate iso_date)
 {
     // 1. Let isoDateTime be CombineISODateAndTimeRecord(isoDate, MidnightTimeRecord()).
     auto iso_date_time = combine_iso_date_and_time_record(iso_date, midnight_time_record());
@@ -453,8 +453,7 @@ ThrowCompletionOr<Crypto::SignedBigInteger> get_start_of_day(VM& vm, String cons
         return move(possible_epoch_nanoseconds[0]);
 
     // 4. Assert: IsOffsetTimeZoneIdentifier(timeZone) is false.
-    auto utf16_time_zone = Utf16String::from_utf8(time_zone);
-    VERIFY(!is_offset_time_zone_identifier(utf16_time_zone));
+    VERIFY(!is_offset_time_zone_identifier(time_zone));
 
     // 5. Let possibleEpochNsAfter be GetNamedTimeZoneEpochNanoseconds(timeZone, isoDateTimeAfter), where isoDateTimeAfter
     //    is the ISO Date-Time Record for which DifferenceISODateTime(isoDateTime, isoDateTimeAfter, "iso8601", hour).[[Time]]
@@ -474,7 +473,7 @@ ThrowCompletionOr<Crypto::SignedBigInteger> get_start_of_day(VM& vm, String cons
 }
 
 // 11.1.15 TimeZoneEquals ( one, two ), https://tc39.es/proposal-temporal/#sec-temporal-timezoneequals
-bool time_zone_equals(StringView one, StringView two)
+bool time_zone_equals(Utf16View one, Utf16View two)
 {
     // 1. If one is two, return true.
     if (one == two)
@@ -482,10 +481,8 @@ bool time_zone_equals(StringView one, StringView two)
 
     // NB: IsOffsetTimeZoneIdentifier simply invokes parse_utc_offset and returns whether it has a value. We do this
     //     manually here so that we can handle the offset minutes assertion below without any extra performance penalty.
-    auto utf16_one = Utf16String::from_utf8(one);
-    auto utf16_two = Utf16String::from_utf8(two);
-    auto time_zone_offset_one = parse_utc_offset(utf16_one, SubMinutePrecision::No);
-    auto time_zone_offset_two = parse_utc_offset(utf16_two, SubMinutePrecision::No);
+    auto time_zone_offset_one = parse_utc_offset(one, SubMinutePrecision::No);
+    auto time_zone_offset_two = parse_utc_offset(two, SubMinutePrecision::No);
 
     // 2. If IsOffsetTimeZoneIdentifier(one) is false and IsOffsetTimeZoneIdentifier(two) is false, then
     if (!time_zone_offset_one.has_value() && !time_zone_offset_two.has_value()) {
@@ -517,38 +514,15 @@ bool time_zone_equals(StringView one, StringView two)
 // OPTIMIZATION: The result of parsing a time zone identifier will not change, so we can cache the result.
 static auto& time_zone_id_cache()
 {
-    static NeverDestroyed<HashMap<String, ParsedTimeZoneIdentifier>> cache;
+    static NeverDestroyed<HashMap<Utf16String, ParsedTimeZoneIdentifier>> cache;
     return *cache;
 }
 
-// 11.1.16 ParseTimeZoneIdentifier ( identifier ), https://tc39.es/proposal-temporal/#sec-parsetimezoneidentifier
-ThrowCompletionOr<ParsedTimeZoneIdentifier> parse_time_zone_identifier(VM& vm, String const& identifier)
-{
-    if (auto result = time_zone_id_cache().get(identifier); result.has_value())
-        return *result;
-
-    // 1. Let parseResult be ParseText(StringToCodePoints(identifier), TimeZoneIdentifier).
-    auto utf16_identifier = Utf16String::from_utf8(identifier);
-    auto parse_result = parse_iso8601(Production::TimeZoneIdentifier, utf16_identifier);
-
-    // 2. If parseResult is a List of errors, throw a RangeError exception.
-    if (!parse_result.has_value())
-        return vm.throw_completion<RangeError>(ErrorType::TemporalInvalidTimeZoneString, identifier);
-
-    auto result = parse_time_zone_identifier(*parse_result);
-    time_zone_id_cache().set(identifier, result);
-
-    return result;
-}
-
 ThrowCompletionOr<ParsedTimeZoneIdentifier> parse_time_zone_identifier(VM& vm, Utf16View identifier)
 {
-    Optional<String> cache_key;
-    if (identifier.is_ascii()) {
-        cache_key = MUST(identifier.to_utf8());
-        if (auto result = time_zone_id_cache().get(*cache_key); result.has_value())
-            return *result;
-    }
+    auto cache_key = Utf16String::from_utf16(identifier);
+    if (auto result = time_zone_id_cache().get(cache_key); result.has_value())
+        return *result;
 
     // 1. Let parseResult be ParseText(StringToCodePoints(identifier), TimeZoneIdentifier).
     auto parse_result = parse_iso8601(Production::TimeZoneIdentifier, identifier);
@@ -558,20 +532,20 @@ ThrowCompletionOr<ParsedTimeZoneIdentifier> parse_time_zone_identifier(VM& vm, U
         return vm.throw_completion<RangeError>(ErrorType::TemporalInvalidTimeZoneString, identifier);
 
     auto result = parse_time_zone_identifier(*parse_result);
-    if (cache_key.has_value())
-        time_zone_id_cache().set(*cache_key, result);
+    time_zone_id_cache().set(move(cache_key), result);
 
     return result;
 }
 
 // 11.1.16 ParseTimeZoneIdentifier ( identifier ), https://tc39.es/proposal-temporal/#sec-parsetimezoneidentifier
-ParsedTimeZoneIdentifier const& parse_time_zone_identifier(String const& identifier)
+ParsedTimeZoneIdentifier const& parse_time_zone_identifier(Utf16View identifier)
 {
+    auto cache_key = Utf16String::from_utf16(identifier);
+
     // OPTIMIZATION: Some callers can assume that parsing will succeed.
-    return time_zone_id_cache().ensure(identifier, [&]() {
+    return time_zone_id_cache().ensure(move(cache_key), [&]() {
         // 1. Let parseResult be ParseText(StringToCodePoints(identifier), TimeZoneIdentifier).
-        auto utf16_identifier = Utf16String::from_utf8(identifier);
-        auto parse_result = parse_iso8601(Production::TimeZoneIdentifier, utf16_identifier);
+        auto parse_result = parse_iso8601(Production::TimeZoneIdentifier, identifier);
         VERIFY(parse_result.has_value());
 
         return parse_time_zone_identifier(*parse_result);
@@ -589,7 +563,7 @@ ParsedTimeZoneIdentifier parse_time_zone_identifier(ParseResult const& parse_res
         // b. NOTE: name is syntactically valid, but does not necessarily conform to IANA Time Zone Database naming
         //    guidelines or correspond with an available named time zone identifier.
         // c. Return Time Zone Identifier Parse Record { [[Name]]: CodePointsToString(name), [[OffsetMinutes]]: EMPTY }.
-        return ParsedTimeZoneIdentifier { .name = MUST(parse_result.time_zone_iana_name->to_utf8()), .offset_minutes = {} };
+        return ParsedTimeZoneIdentifier { .name = Utf16String::from_utf16(*parse_result.time_zone_iana_name), .offset_minutes = {} };
     }
 
     // 4. Assert: parseResult contains a UTCOffset[~SubMinutePrecision] Parse Node.
diff --git a/Libraries/LibJS/Runtime/Temporal/TimeZone.h b/Libraries/LibJS/Runtime/Temporal/TimeZone.h
index 23bc18430a..aef799488c 100644
--- a/Libraries/LibJS/Runtime/Temporal/TimeZone.h
+++ b/Libraries/LibJS/Runtime/Temporal/TimeZone.h
@@ -8,6 +8,7 @@
 #pragma once
 
 #include <AK/String.h>
+#include <AK/Utf16String.h>
 #include <AK/Vector.h>
 #include <LibCrypto/BigInt/SignedBigInteger.h>
 #include <LibJS/Runtime/Completion.h>
@@ -17,26 +18,25 @@
 
 namespace JS::Temporal {
 
-extern String UTC_TIME_ZONE;
+extern Utf16String UTC_TIME_ZONE;
 
 ISODateTime get_iso_parts_from_epoch(Crypto::SignedBigInteger const& epoch_nanoseconds);
-Optional<Crypto::SignedBigInteger> get_named_time_zone_next_transition(String const& time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds);
-Optional<Crypto::SignedBigInteger> get_named_time_zone_previous_transition(String const& time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds);
-String format_offset_time_zone_identifier(i64 offset_minutes, Optional<TimeStyle> = {});
-String format_utc_offset_nanoseconds(i64 offset_nanoseconds);
-String format_date_time_utc_offset_rounded(i64 offset_nanoseconds);
-ThrowCompletionOr<String> to_temporal_time_zone_identifier(VM&, Value temporal_time_zone_like);
-i64 get_offset_nanoseconds_for(String const& time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds);
-ISODateTime get_iso_date_time_for(String const& time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds);
-ThrowCompletionOr<String> to_temporal_time_zone_identifier(VM&, Utf16View temporal_time_zone_like);
-ThrowCompletionOr<Crypto::SignedBigInteger> get_epoch_nanoseconds_for(VM&, String const& time_zone, ISODateTime const&, Disambiguation);
-ThrowCompletionOr<Crypto::SignedBigInteger> disambiguate_possible_epoch_nanoseconds(VM&, Vector<Crypto::SignedBigInteger> possible_epoch_ns, String const& time_zone, ISODateTime const&, Disambiguation);
-ThrowCompletionOr<Vector<Crypto::SignedBigInteger>> get_possible_epoch_nanoseconds(VM&, String const& time_zone, ISODateTime const&);
-ThrowCompletionOr<Crypto::SignedBigInteger> get_start_of_day(VM&, String const& time_zone, ISODate);
-bool time_zone_equals(StringView one, StringView two);
-ThrowCompletionOr<ParsedTimeZoneIdentifier> parse_time_zone_identifier(VM&, String const& identifier);
+Optional<Crypto::SignedBigInteger> get_named_time_zone_next_transition(Utf16View time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds);
+Optional<Crypto::SignedBigInteger> get_named_time_zone_previous_transition(Utf16View time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds);
+Utf16String format_offset_time_zone_identifier(i64 offset_minutes, Optional<TimeStyle> = {});
+Utf16String format_utc_offset_nanoseconds(i64 offset_nanoseconds);
+Utf16String format_date_time_utc_offset_rounded(i64 offset_nanoseconds);
+ThrowCompletionOr<Utf16String> to_temporal_time_zone_identifier(VM&, Value temporal_time_zone_like);
+i64 get_offset_nanoseconds_for(Utf16View time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds);
+ISODateTime get_iso_date_time_for(Utf16View time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds);
+ThrowCompletionOr<Utf16String> to_temporal_time_zone_identifier(VM&, Utf16View temporal_time_zone_like);
+ThrowCompletionOr<Crypto::SignedBigInteger> get_epoch_nanoseconds_for(VM&, Utf16View time_zone, ISODateTime const&, Disambiguation);
+ThrowCompletionOr<Crypto::SignedBigInteger> disambiguate_possible_epoch_nanoseconds(VM&, Vector<Crypto::SignedBigInteger> possible_epoch_ns, Utf16View time_zone, ISODateTime const&, Disambiguation);
+ThrowCompletionOr<Vector<Crypto::SignedBigInteger>> get_possible_epoch_nanoseconds(VM&, Utf16View time_zone, ISODateTime const&);
+ThrowCompletionOr<Crypto::SignedBigInteger> get_start_of_day(VM&, Utf16View time_zone, ISODate);
+bool time_zone_equals(Utf16View one, Utf16View two);
 ThrowCompletionOr<ParsedTimeZoneIdentifier> parse_time_zone_identifier(VM&, Utf16View identifier);
-ParsedTimeZoneIdentifier const& parse_time_zone_identifier(String const& identifier);
+ParsedTimeZoneIdentifier const& parse_time_zone_identifier(Utf16View identifier);
 ParsedTimeZoneIdentifier parse_time_zone_identifier(ParseResult const&);
 
 }
diff --git a/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp b/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp
index bd80450416..f97ed2836b 100644
--- a/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp
@@ -24,7 +24,7 @@ namespace JS::Temporal {
 GC_DEFINE_ALLOCATOR(ZonedDateTime);
 
 // 6 Temporal.ZonedDateTime Objects, https://tc39.es/proposal-temporal/#sec-temporal-zoneddatetime-objects
-ZonedDateTime::ZonedDateTime(BigInt const& epoch_nanoseconds, String time_zone, String calendar, Object& prototype)
+ZonedDateTime::ZonedDateTime(BigInt const& epoch_nanoseconds, Utf16String time_zone, Utf16String calendar, Object& prototype)
     : Object(ConstructWithPrototypeTag::Tag, prototype)
     , m_epoch_nanoseconds(epoch_nanoseconds)
     , m_time_zone(move(time_zone))
@@ -39,7 +39,7 @@ void ZonedDateTime::visit_edges(Cell::Visitor& visitor)
 }
 
 // 6.5.1 InterpretISODateTimeOffset ( isoDate, time, offsetBehaviour, offsetNanoseconds, timeZone, disambiguation, offsetOption, matchBehaviour ), https://tc39.es/proposal-temporal/#sec-temporal-interpretisodatetimeoffset
-ThrowCompletionOr<Crypto::SignedBigInteger> interpret_iso_date_time_offset(VM& vm, ISODate iso_date, Variant<ParsedISODateTime::StartOfDay, Time> const& time_or_start_of_day, OffsetBehavior offset_behavior, double offset_nanoseconds, String const& time_zone, Disambiguation disambiguation, OffsetOption offset_option, MatchBehavior match_behavior)
+ThrowCompletionOr<Crypto::SignedBigInteger> interpret_iso_date_time_offset(VM& vm, ISODate iso_date, Variant<ParsedISODateTime::StartOfDay, Time> const& time_or_start_of_day, OffsetBehavior offset_behavior, double offset_nanoseconds, Utf16View time_zone, Disambiguation disambiguation, OffsetOption offset_option, MatchBehavior match_behavior)
 {
     // 1. If time is START-OF-DAY, then
     if (time_or_start_of_day.has<ParsedISODateTime::StartOfDay>()) {
@@ -137,8 +137,8 @@ ThrowCompletionOr<GC::Ref<ZonedDateTime>> to_temporal_zoned_date_time(VM& vm, Va
     // 3. Let matchBehaviour be MATCH-EXACTLY.
     auto match_behavior = MatchBehavior::MatchExactly;
 
-    String calendar;
-    String time_zone;
+    Utf16String calendar;
+    Utf16String time_zone;
     Optional<Utf16String> offset_string;
 
     Disambiguation disambiguation;
@@ -238,7 +238,7 @@ ThrowCompletionOr<GC::Ref<ZonedDateTime>> to_temporal_zoned_date_time(VM& vm, Va
         // i. If calendar is EMPTY, set calendar to "iso8601".
         calendar = result.calendar.has_value()
             ? TRY(canonicalize_calendar(vm, *result.calendar))
-            : TRY(canonicalize_calendar(vm, "iso8601"sv));
+            : TRY(canonicalize_calendar(vm, ISO8601_CALENDAR));
 
         // k. Set matchBehaviour to MATCH-MINUTES.
         match_behavior = MatchBehavior::MatchMinutes;
@@ -310,7 +310,7 @@ ThrowCompletionOr<GC::Ref<ZonedDateTime>> to_temporal_zoned_date_time(VM& vm, Va
 }
 
 // 6.5.3 CreateTemporalZonedDateTime ( epochNanoseconds, timeZone, calendar [ , newTarget ] ), https://tc39.es/proposal-temporal/#sec-temporal-createtemporalzoneddatetime
-ThrowCompletionOr<GC::Ref<ZonedDateTime>> create_temporal_zoned_date_time(VM& vm, BigInt const& epoch_nanoseconds, String time_zone, String calendar, GC::Ptr<FunctionObject> new_target)
+ThrowCompletionOr<GC::Ref<ZonedDateTime>> create_temporal_zoned_date_time(VM& vm, BigInt const& epoch_nanoseconds, Utf16String time_zone, Utf16String calendar, GC::Ptr<FunctionObject> new_target)
 {
     auto& realm = *vm.current_realm();
 
@@ -332,7 +332,7 @@ ThrowCompletionOr<GC::Ref<ZonedDateTime>> create_temporal_zoned_date_time(VM& vm
 }
 
 // 6.5.4 TemporalZonedDateTimeToString ( zonedDateTime, precision, showCalendar, showTimeZone, showOffset [ , increment [ , unit [ , roundingMode ] ] ] ), https://tc39.es/proposal-temporal/#sec-temporal-temporalzoneddatetimetostring
-String temporal_zoned_date_time_to_string(ZonedDateTime const& zoned_date_time, SecondsStringPrecision::Precision precision, ShowCalendar show_calendar, ShowTimeZoneName show_time_zone, ShowOffset show_offset, u64 increment, Unit unit, RoundingMode rounding_mode)
+Utf16String temporal_zoned_date_time_to_string(ZonedDateTime const& zoned_date_time, SecondsStringPrecision::Precision precision, ShowCalendar show_calendar, ShowTimeZoneName show_time_zone, ShowOffset show_offset, u64 increment, Unit unit, RoundingMode rounding_mode)
 {
     // 1. If increment is not present, set increment to 1.
     // 2. If unit is not present, set unit to NANOSECOND.
@@ -354,8 +354,8 @@ String temporal_zoned_date_time_to_string(ZonedDateTime const& zoned_date_time,
     // 9. Let dateTimeString be ISODateTimeToString(isoDateTime, "iso8601", precision, NEVER).
     auto date_time_string = iso_date_time_to_string(iso_date_time, ISO8601_CALENDAR, precision, ShowCalendar::Never);
 
-    String offset_string;
-    String time_zone_string;
+    Utf16String offset_string;
+    Utf16String time_zone_string;
 
     // 10. If showOffset is NEVER, then
     if (show_offset == ShowOffset::Never) {
@@ -378,18 +378,18 @@ String temporal_zoned_date_time_to_string(ZonedDateTime const& zoned_date_time,
 
         // b. Let timeZoneString be the string-concatenation of the code unit 0x005B (LEFT SQUARE BRACKET), flag,
         //    timeZone, and the code unit 0x005D (RIGHT SQUARE BRACKET).
-        time_zone_string = MUST(String::formatted("[{}{}]", flag, time_zone));
+        time_zone_string = Utf16String::formatted("[{}{}]", flag, time_zone);
     }
 
     // 14. Let calendarString be FormatCalendarAnnotation(zonedDateTime.[[Calendar]], showCalendar).
     auto calendar_string = format_calendar_annotation(zoned_date_time.calendar(), show_calendar);
 
     // 15. Return the string-concatenation of dateTimeString, offsetString, timeZoneString, and calendarString.
-    return MUST(String::formatted("{}{}{}{}", date_time_string, offset_string, time_zone_string, calendar_string));
+    return Utf16String::formatted("{}{}{}{}", date_time_string, offset_string, time_zone_string, calendar_string);
 }
 
 // 6.5.5 AddZonedDateTime ( epochNanoseconds, timeZone, calendar, duration, overflow ), https://tc39.es/proposal-temporal/#sec-temporal-addzoneddatetime
-ThrowCompletionOr<Crypto::SignedBigInteger> add_zoned_date_time(VM& vm, Crypto::SignedBigInteger const& epoch_nanoseconds, String const& time_zone, String const& calendar, InternalDuration const& duration, Overflow overflow)
+ThrowCompletionOr<Crypto::SignedBigInteger> add_zoned_date_time(VM& vm, Crypto::SignedBigInteger const& epoch_nanoseconds, Utf16View time_zone, Utf16View calendar, InternalDuration const& duration, Overflow overflow)
 {
     // 1. If DateDurationSign(duration.[[Date]]) = 0, return ? AddInstant(epochNanoseconds, duration.[[Time]]).
     if (date_duration_sign(duration.date) == 0)
@@ -416,7 +416,7 @@ ThrowCompletionOr<Crypto::SignedBigInteger> add_zoned_date_time(VM& vm, Crypto::
 }
 
 // 6.5.6 DifferenceZonedDateTime ( ns1, ns2, timeZone, calendar, largestUnit ), https://tc39.es/proposal-temporal/#sec-temporal-differencezoneddatetime
-ThrowCompletionOr<InternalDuration> difference_zoned_date_time(VM& vm, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, String const& time_zone, String const& calendar, Unit largest_unit)
+ThrowCompletionOr<InternalDuration> difference_zoned_date_time(VM& vm, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, Utf16View time_zone, Utf16View calendar, Unit largest_unit)
 {
     // 1. If ns1 = ns2, return CombineDateAndTimeDuration(ZeroDateDuration(), 0).
     if (nanoseconds1 == nanoseconds2)
@@ -499,7 +499,7 @@ ThrowCompletionOr<InternalDuration> difference_zoned_date_time(VM& vm, Crypto::S
 }
 
 // 6.5.7 DifferenceZonedDateTimeWithRounding ( ns1, ns2, timeZone, calendar, largestUnit, roundingIncrement, smallestUnit, roundingMode ), https://tc39.es/proposal-temporal/#sec-temporal-differencezoneddatetimewithrounding
-ThrowCompletionOr<InternalDuration> difference_zoned_date_time_with_rounding(VM& vm, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, String const& time_zone, String const& calendar, Unit largest_unit, u64 rounding_increment, Unit smallest_unit, RoundingMode rounding_mode)
+ThrowCompletionOr<InternalDuration> difference_zoned_date_time_with_rounding(VM& vm, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, Utf16View time_zone, Utf16View calendar, Unit largest_unit, u64 rounding_increment, Unit smallest_unit, RoundingMode rounding_mode)
 {
     // 1. If TemporalUnitCategory(largestUnit) is TIME, return DifferenceInstant(ns1, ns2, roundingIncrement, smallestUnit, roundingMode).
     if (temporal_unit_category(largest_unit) == UnitCategory::Time)
@@ -520,7 +520,7 @@ ThrowCompletionOr<InternalDuration> difference_zoned_date_time_with_rounding(VM&
 }
 
 // 6.5.8 DifferenceZonedDateTimeWithTotal ( ns1, ns2, timeZone, calendar, unit ), https://tc39.es/proposal-temporal/#sec-temporal-differencezoneddatetimewithtotal
-ThrowCompletionOr<Crypto::BigFraction> difference_zoned_date_time_with_total(VM& vm, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, String const& time_zone, String const& calendar, Unit unit)
+ThrowCompletionOr<Crypto::BigFraction> difference_zoned_date_time_with_total(VM& vm, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, Utf16View time_zone, Utf16View calendar, Unit unit)
 {
     // 1. If TemporalUnitCategory(unit) is TIME, then
     if (temporal_unit_category(unit) == UnitCategory::Time) {
diff --git a/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.h b/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.h
index d7b1d6be8f..3699b3fb70 100644
--- a/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.h
+++ b/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.h
@@ -7,6 +7,7 @@
 
 #pragma once
 
+#include <AK/Utf16String.h>
 #include <LibCrypto/BigFraction/BigFraction.h>
 #include <LibJS/Runtime/BigInt.h>
 #include <LibJS/Runtime/Completion.h>
@@ -24,17 +25,17 @@ public:
     virtual ~ZonedDateTime() override = default;
 
     [[nodiscard]] GC::Ref<BigInt const> epoch_nanoseconds() const { return m_epoch_nanoseconds; }
-    [[nodiscard]] String const& time_zone() const { return m_time_zone; }
-    [[nodiscard]] String const& calendar() const { return m_calendar; }
+    [[nodiscard]] Utf16String const& time_zone() const { return m_time_zone; }
+    [[nodiscard]] Utf16String const& calendar() const { return m_calendar; }
 
 private:
-    ZonedDateTime(BigInt const& nanoseconds, String time_zone, String calendar, Object& prototype);
+    ZonedDateTime(BigInt const& nanoseconds, Utf16String time_zone, Utf16String calendar, Object& prototype);
 
     virtual void visit_edges(Visitor&) override;
 
     GC::Ref<BigInt const> m_epoch_nanoseconds; // [[EpochNanoseconds]]
-    String m_time_zone;                        // [[TimeZone]]
-    String m_calendar;                         // [[Calendar]]
+    Utf16String m_time_zone;                   // [[TimeZone]]
+    Utf16String m_calendar;                    // [[Calendar]]
 };
 
 enum class OffsetBehavior {
@@ -48,14 +49,14 @@ enum class MatchBehavior {
     MatchMinutes,
 };
 
-ThrowCompletionOr<Crypto::SignedBigInteger> interpret_iso_date_time_offset(VM&, ISODate, Variant<ParsedISODateTime::StartOfDay, Time> const&, OffsetBehavior, double offset_nanoseconds, String const& time_zone, Disambiguation, OffsetOption, MatchBehavior);
+ThrowCompletionOr<Crypto::SignedBigInteger> interpret_iso_date_time_offset(VM&, ISODate, Variant<ParsedISODateTime::StartOfDay, Time> const&, OffsetBehavior, double offset_nanoseconds, Utf16View time_zone, Disambiguation, OffsetOption, MatchBehavior);
 ThrowCompletionOr<GC::Ref<ZonedDateTime>> to_temporal_zoned_date_time(VM&, Value item, Value options = js_undefined());
-ThrowCompletionOr<GC::Ref<ZonedDateTime>> create_temporal_zoned_date_time(VM&, BigInt const& epoch_nanoseconds, String time_zone, String calendar, GC::Ptr<FunctionObject> new_target = {});
-String temporal_zoned_date_time_to_string(ZonedDateTime const&, SecondsStringPrecision::Precision, ShowCalendar, ShowTimeZoneName, ShowOffset, u64 increment = 1, Unit = Unit::Nanosecond, RoundingMode = RoundingMode::Trunc);
-ThrowCompletionOr<Crypto::SignedBigInteger> add_zoned_date_time(VM&, Crypto::SignedBigInteger const& epoch_nanoseconds, String const& time_zone, String const& calendar, InternalDuration const&, Overflow);
-ThrowCompletionOr<InternalDuration> difference_zoned_date_time(VM&, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, String const& time_zone, String const& calendar, Unit largest_unit);
-ThrowCompletionOr<InternalDuration> difference_zoned_date_time_with_rounding(VM&, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, String const& time_zone, String const& calendar, Unit largest_unit, u64 rounding_increment, Unit smallest_unit, RoundingMode);
-ThrowCompletionOr<Crypto::BigFraction> difference_zoned_date_time_with_total(VM&, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, String const& time_zone, String const& calendar, Unit);
+ThrowCompletionOr<GC::Ref<ZonedDateTime>> create_temporal_zoned_date_time(VM&, BigInt const& epoch_nanoseconds, Utf16String time_zone, Utf16String calendar, GC::Ptr<FunctionObject> new_target = {});
+Utf16String temporal_zoned_date_time_to_string(ZonedDateTime const&, SecondsStringPrecision::Precision, ShowCalendar, ShowTimeZoneName, ShowOffset, u64 increment = 1, Unit = Unit::Nanosecond, RoundingMode = RoundingMode::Trunc);
+ThrowCompletionOr<Crypto::SignedBigInteger> add_zoned_date_time(VM&, Crypto::SignedBigInteger const& epoch_nanoseconds, Utf16View time_zone, Utf16View calendar, InternalDuration const&, Overflow);
+ThrowCompletionOr<InternalDuration> difference_zoned_date_time(VM&, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, Utf16View time_zone, Utf16View calendar, Unit largest_unit);
+ThrowCompletionOr<InternalDuration> difference_zoned_date_time_with_rounding(VM&, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, Utf16View time_zone, Utf16View calendar, Unit largest_unit, u64 rounding_increment, Unit smallest_unit, RoundingMode);
+ThrowCompletionOr<Crypto::BigFraction> difference_zoned_date_time_with_total(VM&, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, Utf16View time_zone, Utf16View calendar, Unit);
 ThrowCompletionOr<GC::Ref<Duration>> difference_temporal_zoned_date_time(VM&, DurationOperation, ZonedDateTime const&, Value other, Value options);
 ThrowCompletionOr<GC::Ref<ZonedDateTime>> add_duration_to_zoned_date_time(VM&, ArithmeticOperation, ZonedDateTime const&, Value temporal_duration_like, Value options);
 
diff --git a/Libraries/LibJS/Runtime/Temporal/ZonedDateTimeConstructor.cpp b/Libraries/LibJS/Runtime/Temporal/ZonedDateTimeConstructor.cpp
index 2232c8adc6..27d8c02bf3 100644
--- a/Libraries/LibJS/Runtime/Temporal/ZonedDateTimeConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/ZonedDateTimeConstructor.cpp
@@ -71,7 +71,7 @@ ThrowCompletionOr<GC::Ref<Object>> ZonedDateTimeConstructor::construct(FunctionO
     // 5. Let timeZoneParse be ? ParseTimeZoneIdentifier(timeZone).
     auto time_zone_parse = TRY(parse_time_zone_identifier(vm, time_zone_value.as_string().utf16_string_view()));
 
-    String time_zone;
+    Utf16String time_zone;
 
     // 6. If timeZoneParse.[[OffsetMinutes]] is EMPTY, then
     if (!time_zone_parse.offset_minutes.has_value()) {
@@ -80,7 +80,7 @@ ThrowCompletionOr<GC::Ref<Object>> ZonedDateTimeConstructor::construct(FunctionO
 
         // b. If identifierRecord is EMPTY, throw a RangeError exception.
         if (!identifier_record.has_value())
-            return vm.throw_completion<RangeError>(ErrorType::TemporalInvalidTimeZoneName, *time_zone_parse.name);
+            return vm.throw_completion<RangeError>(ErrorType::TemporalInvalidTimeZoneName, time_zone_parse.name->utf16_view());
 
         // c. Set timeZone to identifierRecord.[[Identifier]].
         time_zone = identifier_record->identifier;
@@ -93,7 +93,7 @@ ThrowCompletionOr<GC::Ref<Object>> ZonedDateTimeConstructor::construct(FunctionO
 
     // 8. If calendar is undefined, set calendar to "iso8601".
     if (calendar_value.is_undefined())
-        calendar_value = PrimitiveString::create(vm, "iso8601"_string);
+        calendar_value = PrimitiveString::create(vm, "iso8601"_utf16_fly_string);
 
     // 9. If calendar is not a String, throw a TypeError exception.
     if (!calendar_value.is_string())
diff --git a/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.cpp b/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.cpp
index 146d724271..2defe537be 100644
--- a/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.cpp
@@ -37,7 +37,7 @@ void ZonedDateTimePrototype::initialize(Realm& realm)
     auto& vm = this->vm();
 
     // 6.3.2 Temporal.ZonedDateTime.prototype[ %Symbol.toStringTag% ], https://tc39.es/proposal-temporal/#sec-temporal.zoneddatetime.prototype-%symbol.tostringtag%
-    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.ZonedDateTime"_string), Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.ZonedDateTime"_utf16_fly_string), Attribute::Configurable);
 
     define_native_accessor(realm, vm.names.calendarId, calendar_id_getter, {}, Attribute::Configurable);
     define_native_accessor(realm, vm.names.timeZoneId, time_zone_id_getter, {}, Attribute::Configurable);
@@ -204,8 +204,7 @@ JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::month_code_getter)
     auto iso_date_time = get_iso_date_time_for(zoned_date_time->time_zone(), zoned_date_time->epoch_nanoseconds()->big_integer());
 
     // 4. Return CalendarISOToDate(zonedDateTime.[[Calendar]], isoDateTime.[[ISODate]]).[[MonthCode]].
-    auto month_code = calendar_iso_to_date(zoned_date_time->calendar(), iso_date_time.iso_date).month_code;
-    return PrimitiveString::create(vm, move(month_code));
+    return PrimitiveString::create(vm, calendar_iso_to_date(zoned_date_time->calendar(), iso_date_time.iso_date).month_code);
 }
 
 // 6.3.11 get Temporal.ZonedDateTime.prototype.hour, https://tc39.es/proposal-temporal/#sec-get-temporal.zoneddatetime.prototype.hour
@@ -416,7 +415,7 @@ JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::with)
     fields.nanosecond = iso_date_time.time.nanosecond;
 
     // 16. Set fields.[[OffsetString]] to FormatUTCOffsetNanoseconds(offsetNanoseconds).
-    fields.offset_string = Utf16String::from_utf8(format_utc_offset_nanoseconds(offset_nanoseconds));
+    fields.offset_string = format_utc_offset_nanoseconds(offset_nanoseconds);
 
     // 17. Let partialZonedDateTime be ? PrepareCalendarFields(calendar, temporalZonedDateTimeLike, « YEAR, MONTH, MONTH-CODE, DAY », « HOUR, MINUTE, SECOND, MILLISECOND, MICROSECOND, NANOSECOND, OFFSET », PARTIAL).
     static constexpr auto calendar_field_names = to_array({ CalendarField::Year, CalendarField::Month, CalendarField::MonthCode, CalendarField::Day });
@@ -806,7 +805,7 @@ JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::to_locale_string)
     auto zoned_date_time = TRY(typed_this_object(vm));
 
     // 3. Let dateTimeFormat be ? CreateDateTimeFormat(%Intl.DateTimeFormat%, locales, options, ANY, ALL, zonedDateTime.[[TimeZone]]).
-    auto date_time_format = TRY(Intl::create_date_time_format(vm, realm.intrinsics().intl_date_time_format_constructor(), locales, options, Intl::OptionRequired::Any, Intl::OptionDefaults::All, zoned_date_time->time_zone()));
+    auto date_time_format = TRY(Intl::create_date_time_format(vm, realm.intrinsics().intl_date_time_format_constructor(), locales, options, Intl::OptionRequired::Any, Intl::OptionDefaults::All, zoned_date_time->time_zone().utf16_view()));
 
     // 4. If zonedDateTime.[[Calendar]] is not "iso8601" and CalendarEquals(zonedDateTime.[[Calendar]], dateTimeFormat.[[Calendar]]) is false, throw a RangeError exception.
     if (zoned_date_time->calendar() != ISO8601_CALENDAR && !calendar_equals(zoned_date_time->calendar(), date_time_format->calendar()))
@@ -901,8 +900,7 @@ JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::get_time_zone_transition)
     auto direction = TRY(get_direction_option(vm, *direction_param));
 
     // 8. If IsOffsetTimeZoneIdentifier(timeZone) is true, return null.
-    auto utf16_time_zone = Utf16String::from_utf8(time_zone);
-    if (is_offset_time_zone_identifier(utf16_time_zone))
+    if (is_offset_time_zone_identifier(time_zone))
         return js_null();
 
     Optional<Crypto::SignedBigInteger> transition;
diff --git a/Libraries/LibJS/Runtime/Uint8Array.cpp b/Libraries/LibJS/Runtime/Uint8Array.cpp
index 9e86c2a133..6d4721f0f8 100644
--- a/Libraries/LibJS/Runtime/Uint8Array.cpp
+++ b/Libraries/LibJS/Runtime/Uint8Array.cpp
@@ -341,16 +341,16 @@ JS_DEFINE_NATIVE_FUNCTION(Uint8ArrayPrototypeHelpers::to_base64)
     }
 
     // 8. Let toEncode be ? GetUint8ArrayBytes(O).
-    String out_ascii;
+    Utf16String out_ascii;
 
     // OPTIMIZATION: If the ArrayBuffer is not shared, we can avoid copying the bytes.
     if (!typed_array->viewed_array_buffer()->is_shared_array_buffer()
         && !typed_array->viewed_array_buffer()->is_detached()) {
         auto to_encode = TRY(get_uint8_array_bytes_view(vm, typed_array));
         if (alphabet == Alphabet::Base64) {
-            out_ascii = MUST(encode_base64(to_encode, omit_padding));
+            out_ascii = MUST(encode_base64_to_utf16(to_encode, omit_padding));
         } else {
-            out_ascii = MUST(encode_base64url(to_encode, omit_padding));
+            out_ascii = MUST(encode_base64url_to_utf16(to_encode, omit_padding));
         }
     } else {
         auto to_encode = TRY(get_uint8_array_bytes(vm, typed_array));
@@ -359,14 +359,14 @@ JS_DEFINE_NATIVE_FUNCTION(Uint8ArrayPrototypeHelpers::to_base64)
         if (alphabet == Alphabet::Base64) {
             // a. Let outAscii be the sequence of code points which results from encoding toEncode according to the base64
             //    encoding specified in section 4 of RFC 4648. Padding is included if and only if omitPadding is false.
-            out_ascii = MUST(encode_base64(to_encode, omit_padding));
+            out_ascii = MUST(encode_base64_to_utf16(to_encode, omit_padding));
         }
         // 10. Else,
         else {
             // a. Assert: alphabet is "base64url".
             // b. Let outAscii be the sequence of code points which results from encoding toEncode according to the base64url
             //    encoding specified in section 5 of RFC 4648. Padding is included if and only if omitPadding is false.
-            out_ascii = MUST(encode_base64url(to_encode, omit_padding));
+            out_ascii = MUST(encode_base64url_to_utf16(to_encode, omit_padding));
         }
     }
 
diff --git a/Libraries/LibJS/Runtime/VM.cpp b/Libraries/LibJS/Runtime/VM.cpp
index 5c78b22a26..118891bc8e 100644
--- a/Libraries/LibJS/Runtime/VM.cpp
+++ b/Libraries/LibJS/Runtime/VM.cpp
@@ -50,7 +50,7 @@ NonnullRefPtr<VM> VM::create()
     ++s_vm_count;
 
     ErrorMessages error_messages {};
-    error_messages[to_underlying(ErrorMessage::OutOfMemory)] = ErrorType::OutOfMemory.message();
+    error_messages[to_underlying(ErrorMessage::OutOfMemory)] = Utf16String::from_utf16(ErrorType::OutOfMemory.message());
 
     auto vm = adopt_ref(*new VM(move(error_messages)));
 
@@ -828,7 +828,7 @@ void VM::load_imported_module(ImportedModuleReferrer referrer, ModuleRequest con
 
         if (module_or_errors.is_error()) {
             VERIFY(module_or_errors.error().size() > 0);
-            return throw_completion<SyntaxError>(module_or_errors.error().first().to_byte_string());
+            return throw_completion<SyntaxError>(module_or_errors.error().first().to_utf16_string());
         }
 
         return module_or_errors.release_value();
diff --git a/Libraries/LibJS/Runtime/VM.h b/Libraries/LibJS/Runtime/VM.h
index 797e9a6868..dfe2023305 100644
--- a/Libraries/LibJS/Runtime/VM.h
+++ b/Libraries/LibJS/Runtime/VM.h
@@ -363,7 +363,11 @@ public:
     template<typename T>
     COLD Completion throw_completion(ErrorType const& type)
     {
-        return throw_completion<T>(type.message());
+        auto& realm = *current_realm();
+        if constexpr (requires { T::create(realm, type.message()); })
+            return throw_completion<T>(type.message());
+        else
+            return throw_completion<T>(Utf16String::from_utf16(type.message()));
     }
 
     template<typename T, typename... Args>
diff --git a/Libraries/LibJS/Runtime/Value.cpp b/Libraries/LibJS/Runtime/Value.cpp
index bd282d5556..492596e5bd 100644
--- a/Libraries/LibJS/Runtime/Value.cpp
+++ b/Libraries/LibJS/Runtime/Value.cpp
@@ -9,7 +9,6 @@
 #include <AK/AllOf.h>
 #include <AK/Array.h>
 #include <AK/Assertions.h>
-#include <AK/ByteString.h>
 #include <AK/CharacterTypes.h>
 #include <AK/NeverDestroyed.h>
 #include <AK/StringBuilder.h>
@@ -255,13 +254,6 @@ void number_to_string(StringBuilder& builder, double d, NumberToStringMode mode)
     number_to_string_impl(builder, d, mode);
 }
 
-String number_to_string(double d, NumberToStringMode mode)
-{
-    StringBuilder builder;
-    number_to_string(builder, d, mode);
-    return MUST(builder.to_string());
-}
-
 Utf16String number_to_utf16_string(double d, NumberToStringMode mode)
 {
     Utf16StringBuilder builder;
@@ -269,13 +261,6 @@ Utf16String number_to_utf16_string(double d, NumberToStringMode mode)
     return builder.to_string();
 }
 
-ByteString number_to_byte_string(double d, NumberToStringMode mode)
-{
-    StringBuilder builder;
-    number_to_string(builder, d, mode);
-    return builder.to_byte_string();
-}
-
 // 7.2.2 IsArray ( argument ), https://tc39.es/ecma262/#sec-isarray
 ThrowCompletionOr<bool> Value::is_array(VM& vm) const
 {
@@ -455,12 +440,6 @@ ThrowCompletionOr<GC::Ref<PrimitiveString>> Value::to_primitive_string(VM& vm)
     return PrimitiveString::create(vm, move(string));
 }
 
-// 7.1.17 ToString ( argument ), https://tc39.es/ecma262/#sec-tostring
-ThrowCompletionOr<ByteString> Value::to_byte_string(VM& vm) const
-{
-    return TRY(to_utf16_string(vm)).to_utf8_but_should_be_ported_to_utf16().to_byte_string();
-}
-
 // 7.1.17 ToString ( argument ), https://tc39.es/ecma262/#sec-tostring
 ThrowCompletionOr<Utf16String> Value::to_utf16_string(VM& vm) const
 {
@@ -489,7 +468,7 @@ ThrowCompletionOr<Utf16String> Value::to_utf16_string(VM& vm) const
         return Utf16String::number(as_i32());
         // 8. If argument is a BigInt, return BigInt::toString(argument, 10).
     case BIGINT_TAG:
-        return Utf16String::from_utf8(MUST(as_bigint().big_integer().to_base(10)));
+        return MUST(as_bigint().big_integer().to_base_utf16(10));
         // 9. Assert: argument is an Object.
     case OBJECT_TAG: {
         // 10. Let primValue be ? ToPrimitive(argument, string).
@@ -554,19 +533,19 @@ ThrowCompletionOr<Value> Value::to_primitive_slow_case(VM& vm, PreferredType pre
 
         // b. If exoticToPrim is not undefined, then
         if (exotic_to_primitive) {
-            auto hint = [&]() -> ByteString {
+            auto hint = [&]() -> Utf16FlyString {
                 switch (preferred_type) {
                 // i. If preferredType is not present, let hint be "default".
                 case PreferredType::Default:
-                    return "default";
+                    return "default"_utf16_fly_string;
                 // ii. Else if preferredType is string, let hint be "string".
                 case PreferredType::String:
-                    return "string";
+                    return "string"_utf16_fly_string;
                 // iii. Else,
                 // 1. Assert: preferredType is number.
                 // 2. Let hint be "number".
                 case PreferredType::Number:
-                    return "number";
+                    return "number"_utf16_fly_string;
                 default:
                     VERIFY_NOT_REACHED();
                 }
diff --git a/Libraries/LibJS/Runtime/Value.h b/Libraries/LibJS/Runtime/Value.h
index 3841b34d93..34212021ff 100644
--- a/Libraries/LibJS/Runtime/Value.h
+++ b/Libraries/LibJS/Runtime/Value.h
@@ -403,7 +403,6 @@ public:
 
     u64 encoded() const { return m_value.encoded; }
 
-    ThrowCompletionOr<ByteString> to_byte_string(VM&) const;
     ThrowCompletionOr<Utf16String> to_utf16_string(VM&) const;
     ThrowCompletionOr<GC::Ref<PrimitiveString>> to_primitive_string(VM&);
     ThrowCompletionOr<Value> to_primitive(VM&, PreferredType preferred_type = PreferredType::Default) const;
@@ -594,9 +593,7 @@ enum class NumberToStringMode {
     WithoutExponent,
 };
 JS_API void number_to_string(StringBuilder&, double, NumberToStringMode = NumberToStringMode::WithExponent);
-[[nodiscard]] JS_API String number_to_string(double, NumberToStringMode = NumberToStringMode::WithExponent);
 [[nodiscard]] JS_API Utf16String number_to_utf16_string(double, NumberToStringMode = NumberToStringMode::WithExponent);
-[[nodiscard]] ByteString number_to_byte_string(double, NumberToStringMode = NumberToStringMode::WithExponent);
 double string_to_number(Utf16View);
 
 inline bool Value::operator==(Value const& value) const { return same_value(*this, value); }
diff --git a/Libraries/LibJS/Runtime/WeakMapConstructor.cpp b/Libraries/LibJS/Runtime/WeakMapConstructor.cpp
index 0449f963d9..413cc1b9ee 100644
--- a/Libraries/LibJS/Runtime/WeakMapConstructor.cpp
+++ b/Libraries/LibJS/Runtime/WeakMapConstructor.cpp
@@ -70,7 +70,7 @@ ThrowCompletionOr<GC::Ref<Object>> WeakMapConstructor::construct(FunctionObject&
             return {};
         }
 
-        return vm.throw_completion<TypeError>(ErrorType::NotAnObject, ByteString::formatted("Iterator value {}", iterator_value));
+        return vm.throw_completion<TypeError>(ErrorType::NotAnObject, Utf16String::formatted("Iterator value {}", iterator_value));
     }));
 
     return map;
diff --git a/Libraries/LibJS/RustIntegration.cpp b/Libraries/LibJS/RustIntegration.cpp
index 9530ee9bb9..f8562ede34 100644
--- a/Libraries/LibJS/RustIntegration.cpp
+++ b/Libraries/LibJS/RustIntegration.cpp
@@ -89,17 +89,17 @@ static void collect_parse_errors(void* ctx, uint8_t const* message, size_t messa
 {
     auto& errors = *static_cast<Vector<ParserError>*>(ctx);
     errors.append({
-        MUST(String::from_utf8({ message, message_len })),
+        Utf16String::from_utf8({ message, message_len }),
         Position { line, column },
     });
 }
 
-// Collects a single parse error as a formatted String (for eval/dynamic function compilation).
+// Collects a single parse error as a formatted Utf16String (for eval/dynamic function compilation).
 static void collect_single_parse_error(void* ctx, uint8_t const* message, size_t message_len, uint32_t line, uint32_t column)
 {
-    auto& error_message = *static_cast<String*>(ctx);
+    auto& error_message = *static_cast<Utf16String*>(ctx);
     if (error_message.is_empty())
-        error_message = MUST(String::formatted("{} (line: {}, column: {})", MUST(String::from_utf8({ message, message_len })), line, column));
+        error_message = Utf16String::formatted("{} (line: {}, column: {})", Utf16String::from_utf8({ message, message_len }), line, column);
 }
 
 // --- Script GDI builder and callbacks ---
@@ -176,7 +176,7 @@ static void bytecode_dump_append_value_bigint(void* ctx, uint64_t encoded)
 {
     auto& builder = *static_cast<JS::RustIntegration::BytecodeDumpBuilder*>(ctx);
     auto value = bit_cast<Value>(encoded);
-    builder.output.append(MUST(value.as_bigint().to_string()));
+    builder.output.append(value.as_bigint().to_utf16_string());
 }
 
 static void bytecode_dump_append_value_fallback(void* ctx, uint64_t encoded)
@@ -697,7 +697,7 @@ Optional<Result<ScriptResult, Vector<ParserError>>> materialize_bytecode_cache_s
     void* exec_ptr = rust_materialize_bytecode_cache_script(blob, &realm.vm(), source_code.ptr(), source_code->length_in_code_units(), &builder.shared_function_data, &builder);
 
     if (!exec_ptr)
-        return Vector<ParserError> { ParserError { "Failed to materialize bytecode cache"_string, {} } };
+        return Vector<ParserError> { ParserError { "Failed to materialize bytecode cache"_utf16, {} } };
 
     builder.collect_shared_function_data();
     builder.result.executable = static_cast<Bytecode::Executable*>(exec_ptr);
@@ -718,7 +718,7 @@ Optional<Result<ScriptResult, Vector<ParserError>>> compile_script(Utf16View sou
     return compile_parsed_script(parsed, source_code, realm);
 }
 
-Optional<Result<EvalResult, String>> compile_eval(
+Optional<Result<EvalResult, Utf16String>> compile_eval(
     PrimitiveString& code_string, VM& vm,
     CallerMode strict_caller, bool in_function, bool in_method,
     bool in_derived_constructor, bool in_class_field_initializer)
@@ -729,7 +729,7 @@ Optional<Result<EvalResult, String>> compile_eval(
 
     GC::DeferGC defer_gc(vm.heap());
     EvalGdiBuilder builder;
-    String parse_error;
+    Utf16String parse_error;
 
     auto const* source_ptr = source_code->utf16_data();
 
@@ -889,7 +889,7 @@ Optional<Result<ModuleResult, Vector<ParserError>>> materialize_bytecode_cache_m
         &builder, &callbacks, &tla_executable);
 
     if (!exec_ptr && !tla_executable)
-        return Vector<ParserError> { ParserError { "Failed to materialize bytecode cache"_string, {} } };
+        return Vector<ParserError> { ParserError { "Failed to materialize bytecode cache"_utf16, {} } };
 
     builder.collect_shared_function_data();
     if (tla_executable) {
@@ -1000,7 +1000,7 @@ Optional<Result<ModuleResult, Vector<ParserError>>> compile_module(StringView so
     return compile_parsed_module(parsed, source_code, realm);
 }
 
-Optional<Result<GC::Ref<SharedFunctionInstanceData>, String>> compile_dynamic_function(
+Optional<Result<GC::Ref<SharedFunctionInstanceData>, Utf16String>> compile_dynamic_function(
     VM& vm, Utf16View source_text, Utf16View parameters_string, Utf16View body_parse_string,
     FunctionKind kind)
 {
@@ -1025,7 +1025,7 @@ Optional<Result<GC::Ref<SharedFunctionInstanceData>, String>> compile_dynamic_fu
     auto const* body_data = prepare_utf16(body_parse_string, body_buf);
 
     GC::DeferGC defer_gc(vm.heap());
-    String parse_error;
+    Utf16String parse_error;
 
     void* sfd_ptr = rust_compile_dynamic_function(
         full_data, full_length,
@@ -1843,10 +1843,10 @@ extern "C" void* rust_compile_regex(
 
     auto parsed_pattern = JS::parse_regex_pattern(pattern, is_unicode, is_unicode_sets);
     if (parsed_pattern.is_error()) {
-        auto msg = MUST(String::formatted("RegExp compile error: {}", parsed_pattern.release_error().error));
-        auto* buf = static_cast<char*>(kmalloc(msg.byte_count() + 1));
-        memcpy(buf, msg.bytes().data(), msg.byte_count());
-        buf[msg.byte_count()] = '\0';
+        auto msg = Utf16String::formatted("RegExp compile error: {}", parsed_pattern.release_error().error).to_byte_string();
+        auto* buf = static_cast<char*>(kmalloc(msg.length() + 1));
+        memcpy(buf, msg.bytes().data(), msg.length());
+        buf[msg.length()] = '\0';
         *error_out = buf;
         return nullptr;
     }
diff --git a/Libraries/LibJS/RustIntegration.h b/Libraries/LibJS/RustIntegration.h
index f830d9a9d3..379e88e144 100644
--- a/Libraries/LibJS/RustIntegration.h
+++ b/Libraries/LibJS/RustIntegration.h
@@ -162,7 +162,7 @@ Optional<Result<ScriptResult, Vector<ParserError>>> compile_script(Utf16View sou
 
 // Compile eval code. Returns nullopt if Rust is not available.
 // On success, the executable's name is set to "eval".
-Optional<Result<EvalResult, String>> compile_eval(
+Optional<Result<EvalResult, Utf16String>> compile_eval(
     PrimitiveString& code_string, VM& vm,
     CallerMode strict_caller, bool in_function, bool in_method,
     bool in_derived_constructor, bool in_class_field_initializer);
@@ -181,7 +181,7 @@ Optional<Result<ModuleResult, Vector<ParserError>>> compile_module(StringView so
 
 // Compile a dynamic function (new Function()).
 // On success, returns a SharedFunctionInstanceData with source_text set.
-JS_API Optional<Result<GC::Ref<SharedFunctionInstanceData>, String>> compile_dynamic_function(
+JS_API Optional<Result<GC::Ref<SharedFunctionInstanceData>, Utf16String>> compile_dynamic_function(
     VM& vm, Utf16View source_text, Utf16View parameters_string, Utf16View body_parse_string,
     FunctionKind kind);
 
diff --git a/Libraries/LibUnicode/Calendar.cpp b/Libraries/LibUnicode/Calendar.cpp
index bf30f31867..37be99f615 100644
--- a/Libraries/LibUnicode/Calendar.cpp
+++ b/Libraries/LibUnicode/Calendar.cpp
@@ -9,32 +9,6 @@
 
 namespace Unicode {
 
-// https://tc39.es/proposal-temporal/#prod-MonthCode
-static constexpr bool is_valid_month_code_string(StringView month_code)
-{
-    // MonthCode :::
-    //     M00L
-    //     M0 NonZeroDigit L[opt]
-    //     M NonZeroDigit DecimalDigit L[opt]
-    auto length = month_code.length();
-
-    if (length != 3 && length != 4)
-        return false;
-
-    if (month_code[0] != 'M')
-        return false;
-
-    if (!is_ascii_digit(month_code[1]) || !is_ascii_digit(month_code[2]))
-        return false;
-
-    if (length == 3 && month_code[1] == '0' && month_code[2] == '0')
-        return false;
-    if (length == 4 && month_code[3] != 'L')
-        return false;
-
-    return true;
-}
-
 static constexpr bool is_valid_month_code_string(Utf16View month_code)
 {
     // MonthCode :::
@@ -60,35 +34,6 @@ static constexpr bool is_valid_month_code_string(Utf16View month_code)
     return true;
 }
 
-// 12.2.1 ParseMonthCode ( argument ), https://tc39.es/proposal-temporal/#sec-temporal-parsemonthcode
-Optional<MonthCode> parse_month_code(StringView month_code)
-{
-    // 3. If ParseText(StringToCodePoints(monthCode), MonthCode) is a List of errors, throw a RangeError exception.
-    if (!is_valid_month_code_string(month_code))
-        return {};
-
-    // 4. Let isLeapMonth be false.
-    auto is_leap_month = false;
-
-    // 5. If the length of monthCode = 4, then
-    if (month_code.length() == 4) {
-        // a. Assert: The fourth code unit of monthCode is 0x004C (LATIN CAPITAL LETTER L).
-        VERIFY(month_code[3] == 'L');
-
-        // b. Set isLeapMonth to true.
-        is_leap_month = true;
-    }
-
-    // 6. Let monthCodeDigits be the substring of monthCode from 1 to 3.
-    auto month_code_digits = month_code.substring_view(1, 2);
-
-    // 7. Let monthNumber be ℝ(StringToNumber(monthCodeDigits)).
-    auto month_number = month_code_digits.to_number<u8>().value();
-
-    // 8. Return the Record { [[MonthNumber]]: monthNumber, [[IsLeapMonth]]: isLeapMonth }.
-    return MonthCode { month_number, is_leap_month };
-}
-
 // 12.2.1 ParseMonthCode ( argument ), https://tc39.es/proposal-temporal/#sec-temporal-parsemonthcode
 Optional<MonthCode> parse_month_code(Utf16View month_code)
 {
@@ -118,7 +63,7 @@ Optional<MonthCode> parse_month_code(Utf16View month_code)
 }
 
 // 12.2.2 CreateMonthCode ( monthNumber, isLeapMonth ), https://tc39.es/proposal-temporal/#sec-temporal-createmonthcode
-String create_month_code(u8 month_number, bool is_leap_month)
+Utf16String create_month_code(u8 month_number, bool is_leap_month)
 {
     // 1. Assert: If isLeapMonth is false, monthNumber > 0.
     if (!is_leap_month)
@@ -130,14 +75,29 @@ String create_month_code(u8 month_number, bool is_leap_month)
     if (is_leap_month) {
         // a. Return the string-concatenation of the code unit 0x004D (LATIN CAPITAL LETTER M), numberPart, and the
         //    code unit 0x004C (LATIN CAPITAL LETTER L).
-        return MUST(String::formatted("M{:02}L", month_number));
+        u8 month_code[] = { 'M', static_cast<u8>('0' + (month_number / 10)), static_cast<u8>('0' + (month_number % 10)), 'L' };
+        return Utf16String::from_ascii_without_validation(month_code);
     }
 
     // 4. Return the string-concatenation of the code unit 0x004D (LATIN CAPITAL LETTER M) and numberPart.
-    return MUST(String::formatted("M{:02}", month_number));
+    u8 month_code[] = { 'M', static_cast<u8>('0' + (month_number / 10)), static_cast<u8>('0' + (month_number % 10)) };
+    return Utf16String::from_ascii_without_validation(month_code);
 }
 
-CalendarDate iso_date_to_calendar_date(String const& calendar, ISODate iso_date)
+static ReadonlyBytes month_code_as_ascii_bytes(Utf16View month_code, Bytes buffer)
+{
+    VERIFY(month_code.length_in_code_units() <= buffer.size());
+
+    for (size_t i = 0; i < month_code.length_in_code_units(); ++i) {
+        auto code_unit = month_code.code_unit_at(i);
+        VERIFY(is_ascii(code_unit));
+        buffer[i] = static_cast<u8>(code_unit);
+    }
+
+    return { buffer.data(), month_code.length_in_code_units() };
+}
+
+CalendarDate iso_date_to_calendar_date(StringView calendar, ISODate iso_date)
 {
     auto result = FFI::icu_iso_date_to_calendar_date(calendar.bytes().data(), calendar.bytes().size(), iso_date.year, iso_date.month, iso_date.day);
 
@@ -146,7 +106,7 @@ CalendarDate iso_date_to_calendar_date(String const& calendar, ISODate iso_date)
         .era_year = {},
         .year = result.year,
         .month = result.month,
-        .month_code = String::from_utf8_without_validation({ result.month_code, result.month_code_length }),
+        .month_code = Utf16String::from_ascii_without_validation({ result.month_code, result.month_code_length }),
         .day = result.day,
         .day_of_week = result.day_of_week,
         .day_of_year = result.day_of_year,
@@ -159,7 +119,7 @@ CalendarDate iso_date_to_calendar_date(String const& calendar, ISODate iso_date)
     };
 }
 
-Optional<ISODate> calendar_date_to_iso_date(String const& calendar, i32 year, u8 month, u8 day)
+Optional<ISODate> calendar_date_to_iso_date(StringView calendar, i32 year, u8 month, u8 day)
 {
     auto result = FFI::icu_calendar_date_to_iso_date(calendar.bytes().data(), calendar.bytes().size(), year, month, day);
     if (!result.has_value)
@@ -168,42 +128,50 @@ Optional<ISODate> calendar_date_to_iso_date(String const& calendar, i32 year, u8
     return ISODate { result.iso_date.year, result.iso_date.month, result.iso_date.day };
 }
 
-Optional<ISODate> iso_year_and_month_code_to_iso_date(String const& calendar, i32 year, StringView month_code, u8 day)
+Optional<ISODate> iso_year_and_month_code_to_iso_date(StringView calendar, i32 year, Utf16View month_code, u8 day)
 {
-    auto result = FFI::icu_iso_year_and_month_code_to_iso_date(calendar.bytes().data(), calendar.bytes().size(), year, month_code.bytes().data(), month_code.length(), day);
+    u8 month_code_buffer[4];
+    auto month_code_bytes = month_code_as_ascii_bytes(month_code, month_code_buffer);
+    auto result = FFI::icu_iso_year_and_month_code_to_iso_date(calendar.bytes().data(), calendar.bytes().size(), year, month_code_bytes.data(), month_code_bytes.size(), day);
     if (!result.has_value)
         return {};
 
     return ISODate { result.iso_date.year, result.iso_date.month, result.iso_date.day };
 }
 
-Optional<ISODate> calendar_year_and_month_code_to_iso_date(String const& calendar, i32 arithmetic_year, StringView month_code, u8 day)
+Optional<ISODate> calendar_year_and_month_code_to_iso_date(StringView calendar, i32 arithmetic_year, Utf16View month_code, u8 day)
 {
-    auto result = FFI::icu_calendar_year_and_month_code_to_iso_date(calendar.bytes().data(), calendar.bytes().size(), arithmetic_year, month_code.bytes().data(), month_code.length(), day);
+    u8 month_code_buffer[4];
+    auto month_code_bytes = month_code_as_ascii_bytes(month_code, month_code_buffer);
+    auto result = FFI::icu_calendar_year_and_month_code_to_iso_date(calendar.bytes().data(), calendar.bytes().size(), arithmetic_year, month_code_bytes.data(), month_code_bytes.size(), day);
     if (!result.has_value)
         return {};
 
     return ISODate { result.iso_date.year, result.iso_date.month, result.iso_date.day };
 }
 
-u8 calendar_months_in_year(String const& calendar, i32 arithmetic_year)
+u8 calendar_months_in_year(StringView calendar, i32 arithmetic_year)
 {
     return FFI::icu_calendar_months_in_year(calendar.bytes().data(), calendar.bytes().size(), arithmetic_year);
 }
 
-u8 calendar_days_in_month(String const& calendar, i32 arithmetic_year, u8 ordinal_month)
+u8 calendar_days_in_month(StringView calendar, i32 arithmetic_year, u8 ordinal_month)
 {
     return FFI::icu_calendar_days_in_month(calendar.bytes().data(), calendar.bytes().size(), arithmetic_year, ordinal_month);
 }
 
-u8 calendar_max_days_in_month_code(String const& calendar, StringView month_code)
+u8 calendar_max_days_in_month_code(StringView calendar, Utf16View month_code)
 {
-    return FFI::icu_calendar_max_days_in_month_code(calendar.bytes().data(), calendar.bytes().size(), month_code.bytes().data(), month_code.length());
+    u8 month_code_buffer[4];
+    auto month_code_bytes = month_code_as_ascii_bytes(month_code, month_code_buffer);
+    return FFI::icu_calendar_max_days_in_month_code(calendar.bytes().data(), calendar.bytes().size(), month_code_bytes.data(), month_code_bytes.size());
 }
 
-bool calendar_year_contains_month_code(String const& calendar, i32 arithmetic_year, StringView month_code)
+bool calendar_year_contains_month_code(StringView calendar, i32 arithmetic_year, Utf16View month_code)
 {
-    return FFI::icu_year_contains_month_code(calendar.bytes().data(), calendar.bytes().size(), arithmetic_year, month_code.bytes().data(), month_code.length());
+    u8 month_code_buffer[4];
+    auto month_code_bytes = month_code_as_ascii_bytes(month_code, month_code_buffer);
+    return FFI::icu_year_contains_month_code(calendar.bytes().data(), calendar.bytes().size(), arithmetic_year, month_code_bytes.data(), month_code_bytes.size());
 }
 
 }
diff --git a/Libraries/LibUnicode/Calendar.h b/Libraries/LibUnicode/Calendar.h
index 6cce86f1c1..22a6ea73c2 100644
--- a/Libraries/LibUnicode/Calendar.h
+++ b/Libraries/LibUnicode/Calendar.h
@@ -8,7 +8,9 @@
 
 #include <AK/Optional.h>
 #include <AK/String.h>
+#include <AK/StringView.h>
 #include <AK/Types.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 
 namespace Unicode {
@@ -34,11 +36,11 @@ struct YearWeek {
 
 // 12.3.1 Calendar Date Records, https://tc39.es/proposal-temporal/#sec-temporal-calendar-date-records
 struct CalendarDate {
-    Optional<String> era;
+    Optional<Utf16String> era;
     Optional<i32> era_year;
     i32 year { 0 };
     u8 month { 0 };
-    String month_code;
+    Utf16String month_code;
     u8 day { 0 };
     u8 day_of_week { 0 };
     u16 day_of_year { 0 };
@@ -50,19 +52,18 @@ struct CalendarDate {
     bool in_leap_year { false };
 };
 
-Optional<MonthCode> parse_month_code(StringView month_code);
 Optional<MonthCode> parse_month_code(Utf16View month_code);
-String create_month_code(u8 month_number, bool is_leap_month);
+Utf16String create_month_code(u8 month_number, bool is_leap_month);
 
-CalendarDate iso_date_to_calendar_date(String const& calendar, ISODate);
-Optional<ISODate> calendar_date_to_iso_date(String const& calendar, i32 year, u8 month, u8 day);
+CalendarDate iso_date_to_calendar_date(StringView calendar, ISODate);
+Optional<ISODate> calendar_date_to_iso_date(StringView calendar, i32 year, u8 month, u8 day);
 
-Optional<ISODate> iso_year_and_month_code_to_iso_date(String const& calendar, i32 year, StringView month_code, u8 day);
-Optional<ISODate> calendar_year_and_month_code_to_iso_date(String const& calendar, i32 arithmetic_year, StringView month_code, u8 day);
+Optional<ISODate> iso_year_and_month_code_to_iso_date(StringView calendar, i32 year, Utf16View month_code, u8 day);
+Optional<ISODate> calendar_year_and_month_code_to_iso_date(StringView calendar, i32 arithmetic_year, Utf16View month_code, u8 day);
 
-u8 calendar_months_in_year(String const& calendar, i32 arithmetic_year);
-u8 calendar_days_in_month(String const& calendar, i32 arithmetic_year, u8 ordinal_month);
-u8 calendar_max_days_in_month_code(String const& calendar, StringView month_code);
-bool calendar_year_contains_month_code(String const& calendar, i32 arithmetic_year, StringView month_code);
+u8 calendar_months_in_year(StringView calendar, i32 arithmetic_year);
+u8 calendar_days_in_month(StringView calendar, i32 arithmetic_year, u8 ordinal_month);
+u8 calendar_max_days_in_month_code(StringView calendar, Utf16View month_code);
+bool calendar_year_contains_month_code(StringView calendar, i32 arithmetic_year, Utf16View month_code);
 
 }
diff --git a/Libraries/LibUnicode/Collator.cpp b/Libraries/LibUnicode/Collator.cpp
index 55e08a0a1c..9f137f0dac 100644
--- a/Libraries/LibUnicode/Collator.cpp
+++ b/Libraries/LibUnicode/Collator.cpp
@@ -20,13 +20,13 @@ Usage usage_from_string(Utf16View usage)
     VERIFY_NOT_REACHED();
 }
 
-StringView usage_to_string(Usage usage)
+Utf16String usage_to_string(Usage usage)
 {
     switch (usage) {
     case Usage::Sort:
-        return "sort"sv;
+        return "sort"_utf16;
     case Usage::Search:
-        return "search"sv;
+        return "search"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -62,17 +62,17 @@ Sensitivity sensitivity_from_string(Utf16View sensitivity)
     VERIFY_NOT_REACHED();
 }
 
-StringView sensitivity_to_string(Sensitivity sensitivity)
+Utf16String sensitivity_to_string(Sensitivity sensitivity)
 {
     switch (sensitivity) {
     case Sensitivity::Base:
-        return "base"sv;
+        return "base"_utf16;
     case Sensitivity::Accent:
-        return "accent"sv;
+        return "accent"_utf16;
     case Sensitivity::Case:
-        return "case"sv;
+        return "case"_utf16;
     case Sensitivity::Variant:
-        return "variant"sv;
+        return "variant"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -114,7 +114,7 @@ static Sensitivity sensitivity_for_collator(icu::Collator const& collator)
     }
 }
 
-CaseFirst case_first_from_string(StringView case_first)
+CaseFirst case_first_from_string(Utf16View case_first)
 {
     if (case_first == "upper"sv)
         return CaseFirst::Upper;
@@ -125,15 +125,15 @@ CaseFirst case_first_from_string(StringView case_first)
     VERIFY_NOT_REACHED();
 }
 
-StringView case_first_to_string(CaseFirst case_first)
+Utf16String case_first_to_string(CaseFirst case_first)
 {
     switch (case_first) {
     case CaseFirst::Upper:
-        return "upper"sv;
+        return "upper"_utf16;
     case CaseFirst::Lower:
-        return "lower"sv;
+        return "lower"_utf16;
     case CaseFirst::False:
-        return "false"sv;
+        return "false"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
diff --git a/Libraries/LibUnicode/Collator.h b/Libraries/LibUnicode/Collator.h
index c683af3047..1b7e9e0c9d 100644
--- a/Libraries/LibUnicode/Collator.h
+++ b/Libraries/LibUnicode/Collator.h
@@ -8,6 +8,7 @@
 
 #include <AK/NonnullOwnPtr.h>
 #include <AK/StringView.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 
 namespace Unicode {
@@ -17,7 +18,7 @@ enum class Usage {
     Search,
 };
 Usage usage_from_string(Utf16View);
-StringView usage_to_string(Usage);
+Utf16String usage_to_string(Usage);
 
 enum class Sensitivity {
     Base,
@@ -26,15 +27,15 @@ enum class Sensitivity {
     Variant,
 };
 Sensitivity sensitivity_from_string(Utf16View);
-StringView sensitivity_to_string(Sensitivity);
+Utf16String sensitivity_to_string(Sensitivity);
 
 enum class CaseFirst {
     Upper,
     Lower,
     False,
 };
-CaseFirst case_first_from_string(StringView);
-StringView case_first_to_string(CaseFirst);
+CaseFirst case_first_from_string(Utf16View);
+Utf16String case_first_to_string(CaseFirst);
 
 class Collator {
 public:
diff --git a/Libraries/LibUnicode/DateTimeFormat.cpp b/Libraries/LibUnicode/DateTimeFormat.cpp
index 8adaacb43a..72444c118f 100644
--- a/Libraries/LibUnicode/DateTimeFormat.cpp
+++ b/Libraries/LibUnicode/DateTimeFormat.cpp
@@ -43,17 +43,17 @@ DateTimeStyle date_time_style_from_string(Utf16View style)
     VERIFY_NOT_REACHED();
 }
 
-StringView date_time_style_to_string(DateTimeStyle style)
+Utf16String date_time_style_to_string(DateTimeStyle style)
 {
     switch (style) {
     case DateTimeStyle::Full:
-        return "full"sv;
+        return "full"_utf16;
     case DateTimeStyle::Long:
-        return "long"sv;
+        return "long"_utf16;
     case DateTimeStyle::Medium:
-        return "medium"sv;
+        return "medium"_utf16;
     case DateTimeStyle::Short:
-        return "short"sv;
+        return "short"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -73,7 +73,7 @@ static constexpr icu::DateFormat::EStyle icu_date_time_style(DateTimeStyle style
     VERIFY_NOT_REACHED();
 }
 
-HourCycle hour_cycle_from_string(StringView hour_cycle)
+HourCycle hour_cycle_from_string(Utf16View hour_cycle)
 {
     if (hour_cycle == "h11"sv)
         return HourCycle::H11;
@@ -86,26 +86,26 @@ HourCycle hour_cycle_from_string(StringView hour_cycle)
     VERIFY_NOT_REACHED();
 }
 
-StringView hour_cycle_to_string(HourCycle hour_cycle)
+Utf16String hour_cycle_to_string(HourCycle hour_cycle)
 {
     switch (hour_cycle) {
     case HourCycle::H11:
-        return "h11"sv;
+        return "h11"_utf16;
     case HourCycle::H12:
-        return "h12"sv;
+        return "h12"_utf16;
     case HourCycle::H23:
-        return "h23"sv;
+        return "h23"_utf16;
     case HourCycle::H24:
-        return "h24"sv;
+        return "h24"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
 
-Optional<HourCycle> default_hour_cycle(StringView locale)
+Optional<HourCycle> default_hour_cycle(Utf16View locale)
 {
     UErrorCode status = U_ZERO_ERROR;
 
-    auto locale_data = LocaleData::for_locale(locale);
+    auto locale_data = LocaleData::for_locale(locale.bytes());
     if (!locale_data.has_value())
         return {};
 
@@ -169,27 +169,27 @@ CalendarPatternStyle calendar_pattern_style_from_string(Utf16View style)
     VERIFY_NOT_REACHED();
 }
 
-StringView calendar_pattern_style_to_string(CalendarPatternStyle style)
+Utf16String calendar_pattern_style_to_string(CalendarPatternStyle style)
 {
     switch (style) {
     case CalendarPatternStyle::Narrow:
-        return "narrow"sv;
+        return "narrow"_utf16;
     case CalendarPatternStyle::Short:
-        return "short"sv;
+        return "short"_utf16;
     case CalendarPatternStyle::Long:
-        return "long"sv;
+        return "long"_utf16;
     case CalendarPatternStyle::Numeric:
-        return "numeric"sv;
+        return "numeric"_utf16;
     case CalendarPatternStyle::TwoDigit:
-        return "2-digit"sv;
+        return "2-digit"_utf16;
     case CalendarPatternStyle::ShortOffset:
-        return "shortOffset"sv;
+        return "shortOffset"_utf16;
     case CalendarPatternStyle::LongOffset:
-        return "longOffset"sv;
+        return "longOffset"_utf16;
     case CalendarPatternStyle::ShortGeneric:
-        return "shortGeneric"sv;
+        return "shortGeneric"_utf16;
     case CalendarPatternStyle::LongGeneric:
-        return "longGeneric"sv;
+        return "longGeneric"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -522,7 +522,7 @@ static T find_regional_values_for_locale(StringView locale, GetRegionalValues&&
 
     if (!language->region.has_value()) {
         if (auto maximized = add_likely_subtags(language->to_string()); maximized.has_value())
-            language = parse_unicode_language_id(*maximized);
+            language = parse_unicode_language_id(maximized->utf16_view().bytes());
     }
 
     if (!language.has_value() || !language->region.has_value())
@@ -538,44 +538,44 @@ static T find_regional_values_for_locale(StringView locale, GetRegionalValues&&
 // type for those partitions.
 static constexpr i32 LITERAL_FIELD = -1;
 
-static constexpr StringView icu_date_time_format_field_to_string(i32 field)
+static Utf16String icu_date_time_format_field_to_string(i32 field)
 {
     switch (field) {
     case LITERAL_FIELD:
-        return "literal"sv;
+        return "literal"_utf16;
     case UDAT_ERA_FIELD:
-        return "era"sv;
+        return "era"_utf16;
     case UDAT_YEAR_FIELD:
     case UDAT_EXTENDED_YEAR_FIELD:
-        return "year"sv;
+        return "year"_utf16;
     case UDAT_YEAR_NAME_FIELD:
-        return "yearName"sv;
+        return "yearName"_utf16;
     case UDAT_RELATED_YEAR_FIELD:
-        return "relatedYear"sv;
+        return "relatedYear"_utf16;
     case UDAT_MONTH_FIELD:
     case UDAT_STANDALONE_MONTH_FIELD:
-        return "month"sv;
+        return "month"_utf16;
     case UDAT_DAY_OF_WEEK_FIELD:
     case UDAT_DOW_LOCAL_FIELD:
     case UDAT_STANDALONE_DAY_FIELD:
-        return "weekday"sv;
+        return "weekday"_utf16;
     case UDAT_DATE_FIELD:
-        return "day"sv;
+        return "day"_utf16;
     case UDAT_AM_PM_FIELD:
     case UDAT_AM_PM_MIDNIGHT_NOON_FIELD:
     case UDAT_FLEXIBLE_DAY_PERIOD_FIELD:
-        return "dayPeriod"sv;
+        return "dayPeriod"_utf16;
     case UDAT_HOUR_OF_DAY1_FIELD:
     case UDAT_HOUR_OF_DAY0_FIELD:
     case UDAT_HOUR1_FIELD:
     case UDAT_HOUR0_FIELD:
-        return "hour"sv;
+        return "hour"_utf16;
     case UDAT_MINUTE_FIELD:
-        return "minute"sv;
+        return "minute"_utf16;
     case UDAT_SECOND_FIELD:
-        return "second"sv;
+        return "second"_utf16;
     case UDAT_FRACTIONAL_SECOND_FIELD:
-        return "fractionalSecond"sv;
+        return "fractionalSecond"_utf16;
     case UDAT_TIMEZONE_FIELD:
     case UDAT_TIMEZONE_RFC_FIELD:
     case UDAT_TIMEZONE_GENERIC_FIELD:
@@ -583,9 +583,9 @@ static constexpr StringView icu_date_time_format_field_to_string(i32 field)
     case UDAT_TIMEZONE_LOCALIZED_GMT_OFFSET_FIELD:
     case UDAT_TIMEZONE_ISO_FIELD:
     case UDAT_TIMEZONE_ISO_LOCAL_FIELD:
-        return "timeZoneName"sv;
+        return "timeZoneName"_utf16;
     default:
-        return "unknown"sv;
+        return "unknown"_utf16;
     }
 }
 
@@ -707,7 +707,7 @@ public:
             Partition partition;
             partition.type = icu_date_time_format_field_to_string(field);
             partition.value = icu_string_to_utf16_string(formatted_time->tempSubStringBetween(begin, end));
-            partition.source = "shared"sv;
+            partition.source = "shared"_utf16;
             result.append(move(partition));
         };
 
@@ -778,11 +778,11 @@ public:
             partition.value = icu_string_to_utf16_string(formatted_time.tempSubStringBetween(begin, end));
 
             if (start_range.has_value() && start_range->contains(begin))
-                partition.source = "startRange"sv;
+                partition.source = "startRange"_utf16;
             else if (end_range.has_value() && end_range->contains(begin))
-                partition.source = "endRange"sv;
+                partition.source = "endRange"_utf16;
             else
-                partition.source = "shared"sv;
+                partition.source = "shared"_utf16;
 
             result.append(move(partition));
         };
@@ -979,11 +979,11 @@ static constexpr Weekday icu_calendar_day_to_weekday(UCalendarDaysOfWeek day)
     VERIFY_NOT_REACHED();
 }
 
-WeekInfo week_info_of_locale(StringView locale)
+WeekInfo week_info_of_locale(Utf16View locale)
 {
     UErrorCode status = U_ZERO_ERROR;
 
-    auto locale_data = LocaleData::for_locale(locale);
+    auto locale_data = LocaleData::for_locale(locale.bytes());
     if (!locale_data.has_value())
         return {};
 
diff --git a/Libraries/LibUnicode/DateTimeFormat.h b/Libraries/LibUnicode/DateTimeFormat.h
index 52d48ba2e9..49812929db 100644
--- a/Libraries/LibUnicode/DateTimeFormat.h
+++ b/Libraries/LibUnicode/DateTimeFormat.h
@@ -26,7 +26,7 @@ enum class DateTimeStyle {
     Short,
 };
 DateTimeStyle date_time_style_from_string(Utf16View);
-StringView date_time_style_to_string(DateTimeStyle);
+Utf16String date_time_style_to_string(DateTimeStyle);
 
 enum class Weekday {
     Sunday,
@@ -44,9 +44,9 @@ enum class HourCycle {
     H23,
     H24,
 };
-HourCycle hour_cycle_from_string(StringView hour_cycle);
-StringView hour_cycle_to_string(HourCycle hour_cycle);
-Optional<HourCycle> default_hour_cycle(StringView locale);
+HourCycle hour_cycle_from_string(Utf16View hour_cycle);
+Utf16String hour_cycle_to_string(HourCycle hour_cycle);
+Optional<HourCycle> default_hour_cycle(Utf16View locale);
 
 enum class CalendarPatternStyle {
     Narrow,
@@ -60,7 +60,7 @@ enum class CalendarPatternStyle {
     LongGeneric,
 };
 CalendarPatternStyle calendar_pattern_style_from_string(Utf16View style);
-StringView calendar_pattern_style_to_string(CalendarPatternStyle style);
+Utf16String calendar_pattern_style_to_string(CalendarPatternStyle style);
 
 struct CalendarPattern {
     enum class Field {
@@ -154,9 +154,9 @@ public:
     virtual ~DateTimeFormat() = default;
 
     struct Partition {
-        StringView type;
+        Utf16String type;
         Utf16String value;
-        StringView source;
+        Utf16String source;
     };
 
     virtual CalendarPattern const& chosen_pattern() const = 0;
@@ -176,6 +176,6 @@ struct WeekInfo {
     Optional<Weekday> first_day_of_week;
     Vector<Weekday> weekend_days;
 };
-WeekInfo week_info_of_locale(StringView locale);
+WeekInfo week_info_of_locale(Utf16View locale);
 
 }
diff --git a/Libraries/LibUnicode/DisplayNames.cpp b/Libraries/LibUnicode/DisplayNames.cpp
index 0f8a55ec48..673355cdc6 100644
--- a/Libraries/LibUnicode/DisplayNames.cpp
+++ b/Libraries/LibUnicode/DisplayNames.cpp
@@ -25,25 +25,31 @@ LanguageDisplay language_display_from_string(Utf16View language_display)
     VERIFY_NOT_REACHED();
 }
 
-StringView language_display_to_string(LanguageDisplay language_display)
+Utf16String language_display_to_string(LanguageDisplay language_display)
 {
     switch (language_display) {
     case LanguageDisplay::Standard:
-        return "standard"sv;
+        return "standard"_utf16;
     case LanguageDisplay::Dialect:
-        return "dialect"sv;
+        return "dialect"_utf16;
     default:
         VERIFY_NOT_REACHED();
     }
 }
 
-Optional<Utf16String> language_display_name(StringView locale, StringView language, LanguageDisplay display)
+static String string_from_ascii_view(Utf16View string)
+{
+    return MUST(string.to_utf8());
+}
+
+Optional<Utf16String> language_display_name(StringView locale, Utf16View language, LanguageDisplay display)
 {
     auto locale_data = LocaleData::for_locale(locale);
     if (!locale_data.has_value())
         return {};
 
-    auto language_data = LocaleData::for_locale(language);
+    auto language_string = string_from_ascii_view(language);
+    auto language_data = LocaleData::for_locale(language_string.bytes_as_string_view());
     if (!language_data.has_value())
         return {};
 
@@ -57,7 +63,7 @@ Optional<Utf16String> language_display_name(StringView locale, StringView langua
     return icu_string_to_utf16_string(result);
 }
 
-Optional<Utf16String> region_display_name(StringView locale, StringView region)
+Optional<Utf16String> region_display_name(StringView locale, Utf16View region)
 {
     UErrorCode status = U_ZERO_ERROR;
 
@@ -65,7 +71,8 @@ Optional<Utf16String> region_display_name(StringView locale, StringView region)
     if (!locale_data.has_value())
         return {};
 
-    auto icu_region = icu::LocaleBuilder().setRegion(icu_string_piece(region)).build(status);
+    auto region_string = string_from_ascii_view(region);
+    auto icu_region = icu::LocaleBuilder().setRegion(icu_string_piece(region_string.bytes_as_string_view())).build(status);
     if (icu_failure(status))
         return {};
 
@@ -75,7 +82,7 @@ Optional<Utf16String> region_display_name(StringView locale, StringView region)
     return icu_string_to_utf16_string(result);
 }
 
-Optional<Utf16String> script_display_name(StringView locale, StringView script)
+Optional<Utf16String> script_display_name(StringView locale, Utf16View script)
 {
     UErrorCode status = U_ZERO_ERROR;
 
@@ -83,7 +90,8 @@ Optional<Utf16String> script_display_name(StringView locale, StringView script)
     if (!locale_data.has_value())
         return {};
 
-    auto icu_script = icu::LocaleBuilder().setScript(icu_string_piece(script)).build(status);
+    auto script_string = string_from_ascii_view(script);
+    auto icu_script = icu::LocaleBuilder().setScript(icu_string_piece(script_string.bytes_as_string_view())).build(status);
     if (icu_failure(status))
         return {};
 
@@ -93,26 +101,27 @@ Optional<Utf16String> script_display_name(StringView locale, StringView script)
     return icu_string_to_utf16_string(result);
 }
 
-Optional<Utf16String> calendar_display_name(StringView locale, StringView calendar)
+Optional<Utf16String> calendar_display_name(StringView locale, Utf16View calendar)
 {
     auto locale_data = LocaleData::for_locale(locale);
     if (!locale_data.has_value())
         return {};
 
     if (calendar == "gregory"sv)
-        calendar = "gregorian"sv;
+        return calendar_display_name(locale, "gregorian"sv);
     if (calendar == "islamicc"sv)
-        calendar = "islamic-civil"sv;
+        return calendar_display_name(locale, "islamic-civil"sv);
     if (calendar == "ethioaa"sv)
-        calendar = "ethiopic-amete-alem"sv;
+        return calendar_display_name(locale, "ethiopic-amete-alem"sv);
 
     icu::UnicodeString result;
-    locale_data->standard_display_names().keyValueDisplayName("calendar", ByteString(calendar).characters(), result);
+    auto calendar_string = string_from_ascii_view(calendar);
+    locale_data->standard_display_names().keyValueDisplayName("calendar", calendar_string.to_byte_string().characters(), result);
 
     return icu_string_to_utf16_string(result);
 }
 
-static constexpr UDateTimePatternField icu_date_time_field(StringView field)
+static constexpr UDateTimePatternField icu_date_time_field(Utf16View field)
 {
     if (field == "day"sv)
         return UDATPG_DAY_FIELD;
@@ -155,7 +164,7 @@ static constexpr UDateTimePGDisplayWidth icu_date_time_style(Style style)
     VERIFY_NOT_REACHED();
 }
 
-Optional<Utf16String> date_time_field_display_name(StringView locale, StringView field, Style style)
+Optional<Utf16String> date_time_field_display_name(StringView locale, Utf16View field, Style style)
 {
     auto locale_data = LocaleData::for_locale(locale);
     if (!locale_data.has_value())
@@ -186,16 +195,29 @@ Optional<Utf16String> time_zone_display_name(StringView locale, StringView time_
     return icu_string_to_utf16_string(time_zone_name);
 }
 
-static constexpr Array<UChar, 4> icu_currency_code(StringView currency)
+template<typename ViewType>
+static Array<UChar, 4> icu_currency_code(ViewType currency)
 {
-    VERIFY(currency.length() == 3);
+    if constexpr (IsSame<ViewType, Utf16View>)
+        VERIFY(currency.length_in_code_units() == 3);
+    else
+        VERIFY(currency.length() == 3);
 
-    return to_array({
-        static_cast<UChar>(currency[0]),
-        static_cast<UChar>(currency[1]),
-        static_cast<UChar>(currency[2]),
-        u'\0',
-    });
+    if constexpr (IsSame<ViewType, Utf16View>) {
+        return to_array({
+            static_cast<UChar>(currency.code_unit_at(0)),
+            static_cast<UChar>(currency.code_unit_at(1)),
+            static_cast<UChar>(currency.code_unit_at(2)),
+            u'\0',
+        });
+    } else {
+        return to_array({
+            static_cast<UChar>(currency[0]),
+            static_cast<UChar>(currency[1]),
+            static_cast<UChar>(currency[2]),
+            u'\0',
+        });
+    }
 }
 
 static constexpr UCurrNameStyle icu_currency_style(Style style)
@@ -212,7 +234,7 @@ static constexpr UCurrNameStyle icu_currency_style(Style style)
     VERIFY_NOT_REACHED();
 }
 
-Optional<Utf16String> currency_display_name(StringView locale, StringView currency, Style style)
+Optional<Utf16String> currency_display_name(StringView locale, Utf16View currency, Style style)
 {
     UErrorCode status = U_ZERO_ERROR;
 
diff --git a/Libraries/LibUnicode/DisplayNames.h b/Libraries/LibUnicode/DisplayNames.h
index d337949b41..c21ee41a38 100644
--- a/Libraries/LibUnicode/DisplayNames.h
+++ b/Libraries/LibUnicode/DisplayNames.h
@@ -21,15 +21,15 @@ enum class LanguageDisplay {
 };
 
 LanguageDisplay language_display_from_string(Utf16View language_display);
-StringView language_display_to_string(LanguageDisplay language_display);
+Utf16String language_display_to_string(LanguageDisplay language_display);
 
-Optional<Utf16String> language_display_name(StringView locale, StringView language, LanguageDisplay);
-Optional<Utf16String> region_display_name(StringView locale, StringView region);
-Optional<Utf16String> script_display_name(StringView locale, StringView script);
-Optional<Utf16String> calendar_display_name(StringView locale, StringView calendar);
-Optional<Utf16String> date_time_field_display_name(StringView locale, StringView field, Style);
+Optional<Utf16String> language_display_name(StringView locale, Utf16View language, LanguageDisplay);
+Optional<Utf16String> region_display_name(StringView locale, Utf16View region);
+Optional<Utf16String> script_display_name(StringView locale, Utf16View script);
+Optional<Utf16String> calendar_display_name(StringView locale, Utf16View calendar);
+Optional<Utf16String> date_time_field_display_name(StringView locale, Utf16View field, Style);
 Optional<Utf16String> time_zone_display_name(StringView locale, StringView time_zone_identifier, TimeZoneOffset::InDST, double time);
-Optional<Utf16String> currency_display_name(StringView locale, StringView currency, Style);
+Optional<Utf16String> currency_display_name(StringView locale, Utf16View currency, Style);
 Optional<Utf16String> currency_numeric_display_name(StringView locale, StringView currency);
 
 }
diff --git a/Libraries/LibUnicode/DurationFormat.cpp b/Libraries/LibUnicode/DurationFormat.cpp
index 0644d82be2..cb2d4f40b5 100644
--- a/Libraries/LibUnicode/DurationFormat.cpp
+++ b/Libraries/LibUnicode/DurationFormat.cpp
@@ -22,11 +22,11 @@ static constexpr bool is_not_ascii_digit(u32 code_point)
     return !is_ascii_digit(code_point);
 }
 
-DigitalFormat digital_format(StringView locale)
+DigitalFormat digital_format(Utf16View locale)
 {
     UErrorCode status = U_ZERO_ERROR;
 
-    auto locale_data = LocaleData::for_locale(locale);
+    auto locale_data = LocaleData::for_locale(locale.bytes());
     if (!locale_data.has_value())
         return {};
 
@@ -38,7 +38,7 @@ DigitalFormat digital_format(StringView locale)
     rounding_options.min_significant_digits = 1;
     rounding_options.max_significant_digits = 2;
 
-    auto number_formatter = NumberFormat::create(locale, {}, rounding_options);
+    auto number_formatter = NumberFormat::create(locale.bytes(), {}, rounding_options);
 
     auto icu_locale = adopt_own(*locale_data->locale().clone());
     icu_locale->setUnicodeKeywordValue("nu", "latn", status);
diff --git a/Libraries/LibUnicode/DurationFormat.h b/Libraries/LibUnicode/DurationFormat.h
index c0d11e2e4c..88ccd9f19c 100644
--- a/Libraries/LibUnicode/DurationFormat.h
+++ b/Libraries/LibUnicode/DurationFormat.h
@@ -7,6 +7,7 @@
 #pragma once
 
 #include <AK/Utf16String.h>
+#include <AK/Utf16View.h>
 
 namespace Unicode {
 
@@ -16,6 +17,6 @@ struct DigitalFormat {
     bool uses_two_digit_hours { false };
 };
 
-DigitalFormat digital_format(StringView locale);
+DigitalFormat digital_format(Utf16View locale);
 
 }
diff --git a/Libraries/LibUnicode/ICU.cpp b/Libraries/LibUnicode/ICU.cpp
index b1f66bfed9..17a520fc99 100644
--- a/Libraries/LibUnicode/ICU.cpp
+++ b/Libraries/LibUnicode/ICU.cpp
@@ -26,7 +26,7 @@ static auto& locale_cache()
 
 static auto& time_zone_cache()
 {
-    static NeverDestroyed<HashMap<String, OwnPtr<TimeZoneData>>> cache;
+    static NeverDestroyed<HashMap<Utf16String, OwnPtr<TimeZoneData>>> cache;
     return *cache;
 }
 
@@ -56,7 +56,7 @@ LocaleData::LocaleData(icu::Locale locale)
 {
 }
 
-String LocaleData::canonicalize(StringView locale)
+Utf16String LocaleData::canonicalize(StringView locale)
 {
     auto locale_data = LocaleData::for_locale(locale);
     VERIFY(locale_data.has_value());
@@ -70,7 +70,7 @@ String LocaleData::canonicalize(StringView locale)
     //        for all keywords (and then remove "true" per UTS 35). Per CLDR BCP47 data, only specific keys define "yes"
     //        as an alias for "true" (kb, kc, kh, kk, kn). For other keys, "yes" must be preserved. See:
     //        https://unicode-org.atlassian.net/browse/ICU-21367
-    HashTable<ByteString> keywords_with_yes;
+    HashTable<Utf16String> keywords_with_yes;
 
     if (auto parsed = parse_unicode_locale_id(locale); parsed.has_value()) {
         parsed->for_each_extension_of_type<LocaleExtension>([&](auto const& extension) {
@@ -78,9 +78,10 @@ String LocaleData::canonicalize(StringView locale)
                 if (!keyword.value.equals_ignoring_ascii_case("yes"sv))
                     continue;
 
-                auto key = keyword.key.to_ascii_lowercase().to_byte_string();
+                auto key = keyword.key.to_ascii_lowercase();
 
-                if (auto const* legacy_key = uloc_toLegacyKey(key.characters())) {
+                auto key_bytes = MUST(key.utf16_view().to_byte_string());
+                if (auto const* legacy_key = uloc_toLegacyKey(key_bytes.characters())) {
                     if (auto const* value = uloc_toUnicodeLocaleType(legacy_key, "yes"); !value || value != "true"sv)
                         keywords_with_yes.set(move(key));
                 }
@@ -97,21 +98,21 @@ String LocaleData::canonicalize(StringView locale)
     verify_icu_success(status);
 
     if (keywords_with_yes.is_empty()) {
-        locale_data->m_canonical_locale_string = MUST(result.to_string());
+        locale_data->m_canonical_locale_string = Utf16String::from_ascii_without_validation(result.string_view().bytes());
     } else {
         auto parsed = parse_unicode_locale_id(result.string_view());
         VERIFY(parsed.has_value());
 
         parsed->for_each_extension_of_type<LocaleExtension>([&](auto& extension) {
             for (auto& keyword : extension.keywords) {
-                if (keyword.value.is_empty() && keywords_with_yes.contains(keyword.key.bytes_as_string_view()))
-                    keyword.value = "yes"_string;
+                if (keyword.value.is_empty() && keywords_with_yes.contains(keyword.key))
+                    keyword.value = "yes"_utf16;
             }
 
             return IterationDecision::Continue;
         });
 
-        locale_data->m_canonical_locale_string = parsed->to_string();
+        locale_data->m_canonical_locale_string = parsed->to_utf16_string();
     }
 
     return *locale_data->m_canonical_locale_string;
@@ -172,12 +173,13 @@ icu::TimeZoneNames& LocaleData::time_zone_names()
     return *m_time_zone_names;
 }
 
-Optional<TimeZoneData&> TimeZoneData::for_time_zone(StringView time_zone)
+Optional<TimeZoneData&> TimeZoneData::for_time_zone(Utf16View time_zone)
 {
     auto time_zone_data = time_zone_cache().get(time_zone);
 
     if (!time_zone_data.has_value()) {
-        time_zone_data = time_zone_cache().ensure(MUST(String::from_utf8(time_zone)), [&]() -> OwnPtr<TimeZoneData> {
+        auto time_zone_key = Utf16String::from_utf16(time_zone);
+        time_zone_data = time_zone_cache().ensure(move(time_zone_key), [&]() -> OwnPtr<TimeZoneData> {
             auto icu_time_zone = adopt_own_if_nonnull(icu::TimeZone::createTimeZone(icu_string(time_zone)));
             if (!icu_time_zone || *icu_time_zone == icu::TimeZone::getUnknown())
                 return nullptr;
diff --git a/Libraries/LibUnicode/ICU.h b/Libraries/LibUnicode/ICU.h
index cf44bd1742..ea37b76cff 100644
--- a/Libraries/LibUnicode/ICU.h
+++ b/Libraries/LibUnicode/ICU.h
@@ -12,6 +12,7 @@
 #include <AK/String.h>
 #include <AK/StringView.h>
 #include <AK/Utf16String.h>
+#include <AK/Utf16View.h>
 #include <AK/Vector.h>
 #include <LibUnicode/DurationFormat.h>
 
@@ -37,7 +38,7 @@ namespace Unicode {
 class LocaleData {
 public:
     static Optional<LocaleData&> for_locale(StringView locale);
-    static String canonicalize(StringView locale);
+    static Utf16String canonicalize(StringView locale);
 
     ALWAYS_INLINE icu::Locale& locale() { return m_locale; }
 
@@ -57,7 +58,7 @@ private:
     explicit LocaleData(icu::Locale locale);
 
     icu::Locale m_locale;
-    Optional<String> m_canonical_locale_string;
+    Optional<Utf16String> m_canonical_locale_string;
 
     OwnPtr<icu::LocaleDisplayNames> m_standard_display_names;
     OwnPtr<icu::LocaleDisplayNames> m_dialect_display_names;
@@ -69,7 +70,7 @@ private:
 
 class TimeZoneData {
 public:
-    static Optional<TimeZoneData&> for_time_zone(StringView time_zone);
+    static Optional<TimeZoneData&> for_time_zone(Utf16View time_zone);
 
     ALWAYS_INLINE icu::TimeZone& time_zone() { return *m_time_zone; }
 
diff --git a/Libraries/LibUnicode/ListFormat.cpp b/Libraries/LibUnicode/ListFormat.cpp
index e12d11b2bb..dd31f886a8 100644
--- a/Libraries/LibUnicode/ListFormat.cpp
+++ b/Libraries/LibUnicode/ListFormat.cpp
@@ -34,15 +34,15 @@ ListFormatType list_format_type_from_string(Utf16View list_format_type)
     VERIFY_NOT_REACHED();
 }
 
-StringView list_format_type_to_string(ListFormatType list_format_type)
+Utf16String list_format_type_to_string(ListFormatType list_format_type)
 {
     switch (list_format_type) {
     case ListFormatType::Conjunction:
-        return "conjunction"sv;
+        return "conjunction"_utf16;
     case ListFormatType::Disjunction:
-        return "disjunction"sv;
+        return "disjunction"_utf16;
     case ListFormatType::Unit:
-        return "unit"sv;
+        return "unit"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -73,13 +73,13 @@ static constexpr UListFormatterWidth icu_list_format_width(Style style)
     VERIFY_NOT_REACHED();
 }
 
-static constexpr StringView icu_list_format_field_to_string(i32 field)
+static Utf16String icu_list_format_field_to_string(i32 field)
 {
     switch (field) {
     case ULISTFMT_LITERAL_FIELD:
-        return "literal"sv;
+        return "literal"_utf16;
     case ULISTFMT_ELEMENT_FIELD:
-        return "element"sv;
+        return "element"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
diff --git a/Libraries/LibUnicode/ListFormat.h b/Libraries/LibUnicode/ListFormat.h
index 8a8a6172d9..c1309d6bc1 100644
--- a/Libraries/LibUnicode/ListFormat.h
+++ b/Libraries/LibUnicode/ListFormat.h
@@ -20,7 +20,7 @@ enum class ListFormatType {
 };
 ListFormatType list_format_type_from_string(StringView);
 ListFormatType list_format_type_from_string(Utf16View);
-StringView list_format_type_to_string(ListFormatType);
+Utf16String list_format_type_to_string(ListFormatType);
 
 class ListFormat {
 public:
@@ -28,7 +28,7 @@ public:
     virtual ~ListFormat() = default;
 
     struct Partition {
-        StringView type;
+        Utf16String type;
         Utf16String value;
     };
 
diff --git a/Libraries/LibUnicode/Locale.cpp b/Libraries/LibUnicode/Locale.cpp
index d92e3052bd..866d28e592 100644
--- a/Libraries/LibUnicode/Locale.cpp
+++ b/Libraries/LibUnicode/Locale.cpp
@@ -10,6 +10,7 @@
 #include <AK/NeverDestroyed.h>
 #include <AK/QuickSort.h>
 #include <AK/StringBuilder.h>
+#include <AK/Utf16StringBuilder.h>
 #include <LibUnicode/ICU.h>
 #include <LibUnicode/Locale.h>
 
@@ -36,14 +37,14 @@ static constexpr u32 view_code_unit_at(ViewType const& view, size_t index)
         return static_cast<u8>(view[index]);
 }
 
-static String string_from_ascii_view(StringView string)
+static Utf16String utf16_string_from_ascii_view(StringView string)
 {
-    return MUST(String::from_utf8(string));
+    return Utf16String::from_ascii_without_validation(string.bytes());
 }
 
-static String string_from_ascii_view(Utf16View string)
+static Utf16String utf16_string_from_ascii_view(Utf16View string)
 {
-    return MUST(string.to_utf8());
+    return Utf16String::from_utf16(string);
 }
 
 template<typename ViewType>
@@ -205,10 +206,10 @@ static Optional<LanguageID> parse_unicode_language_id_from_lexer(Lexer& lexer)
         case ParseState::ParsingLanguageOrScript:
             if (is_unicode_language_subtag(*segment)) {
                 state = ParseState::ParsingScript;
-                language_id.language = string_from_ascii_view(*segment);
+                language_id.language = utf16_string_from_ascii_view(*segment);
             } else if (is_unicode_script_subtag(*segment)) {
                 state = ParseState::ParsingRegion;
-                language_id.script = string_from_ascii_view(*segment);
+                language_id.script = utf16_string_from_ascii_view(*segment);
             } else {
                 return {};
             }
@@ -217,7 +218,7 @@ static Optional<LanguageID> parse_unicode_language_id_from_lexer(Lexer& lexer)
         case ParseState::ParsingScript:
             if (is_unicode_script_subtag(*segment)) {
                 state = ParseState::ParsingRegion;
-                language_id.script = string_from_ascii_view(*segment);
+                language_id.script = utf16_string_from_ascii_view(*segment);
                 break;
             }
 
@@ -227,7 +228,7 @@ static Optional<LanguageID> parse_unicode_language_id_from_lexer(Lexer& lexer)
         case ParseState::ParsingRegion:
             if (is_unicode_region_subtag(*segment)) {
                 state = ParseState::ParsingVariant;
-                language_id.region = string_from_ascii_view(*segment);
+                language_id.region = utf16_string_from_ascii_view(*segment);
                 break;
             }
 
@@ -236,7 +237,7 @@ static Optional<LanguageID> parse_unicode_language_id_from_lexer(Lexer& lexer)
 
         case ParseState::ParsingVariant:
             if (is_unicode_variant_subtag(*segment)) {
-                language_id.variants.append(string_from_ascii_view(*segment));
+                language_id.variants.append(utf16_string_from_ascii_view(*segment));
             } else {
                 lexer.retreat(view_length(*segment) + 1);
                 state = ParseState::Done;
@@ -279,7 +280,7 @@ static Optional<LocaleExtension> parse_unicode_locale_extension(Lexer& lexer)
         switch (state) {
         case ParseState::ParsingAttribute:
             if (is_attribute(*segment)) {
-                locale_extension.attributes.append(string_from_ascii_view(*segment));
+                locale_extension.attributes.append(utf16_string_from_ascii_view(*segment));
                 break;
             }
 
@@ -288,8 +289,8 @@ static Optional<LocaleExtension> parse_unicode_locale_extension(Lexer& lexer)
 
         case ParseState::ParsingKeyword: {
             // keyword = key (sep type)?
-            Keyword keyword { .key = string_from_ascii_view(*segment) };
-            Vector<String> keyword_values;
+            Keyword keyword { .key = utf16_string_from_ascii_view(*segment) };
+            Vector<Utf16String> keyword_values;
 
             if (!is_key(*segment)) {
                 lexer.retreat(view_length(*segment) + 1);
@@ -306,12 +307,10 @@ static Optional<LocaleExtension> parse_unicode_locale_extension(Lexer& lexer)
                     break;
                 }
 
-                keyword_values.append(string_from_ascii_view(*type));
+                keyword_values.append(utf16_string_from_ascii_view(*type));
             }
 
-            StringBuilder builder;
-            builder.join('-', keyword_values);
-            keyword.value = MUST(builder.to_string());
+            keyword.value = Utf16String::join("-"sv, keyword_values);
 
             locale_extension.keywords.append(move(keyword));
             break;
@@ -366,8 +365,8 @@ static Optional<TransformedExtension> parse_transformed_extension(Lexer& lexer)
 
         case ParseState::ParsingField: {
             // tfield = tkey tvalue;
-            TransformedField field { .key = string_from_ascii_view(*segment) };
-            Vector<String> field_values;
+            TransformedField field { .key = utf16_string_from_ascii_view(*segment) };
+            Vector<Utf16String> field_values;
 
             if (!is_transformed_key(*segment)) {
                 lexer.retreat(view_length(*segment) + 1);
@@ -384,15 +383,13 @@ static Optional<TransformedExtension> parse_transformed_extension(Lexer& lexer)
                     break;
                 }
 
-                field_values.append(string_from_ascii_view(*value));
+                field_values.append(utf16_string_from_ascii_view(*value));
             }
 
             if (field_values.is_empty())
                 return {};
 
-            StringBuilder builder;
-            builder.join('-', field_values);
-            field.value = MUST(builder.to_string());
+            field.value = Utf16String::join("-"sv, field_values);
 
             transformed_extension.fields.append(move(field));
             break;
@@ -414,7 +411,7 @@ static Optional<OtherExtension> parse_other_extension(u32 key, Lexer& lexer)
     // https://unicode.org/reports/tr35/#other_extensions
     //
     // other_extensions = sep [alphanum-[tTuUxX]] (sep alphanum{2,8})+ ;
-    Vector<String> other_values;
+    Vector<Utf16String> other_values;
 
     if (!is_ascii_alphanumeric(key) || (key == 'x') || (key == 'X'))
         return {};
@@ -431,15 +428,13 @@ static Optional<OtherExtension> parse_other_extension(u32 key, Lexer& lexer)
             break;
         }
 
-        other_values.append(string_from_ascii_view(*segment));
+        other_values.append(utf16_string_from_ascii_view(*segment));
     }
 
     if (other_values.is_empty())
         return {};
 
-    StringBuilder builder;
-    builder.join('-', other_values);
-    other_extension.value = MUST(builder.to_string());
+    other_extension.value = Utf16String::join("-"sv, other_values);
 
     return other_extension;
 }
@@ -478,7 +473,7 @@ static Optional<Extension> parse_extension(Lexer& lexer)
 }
 
 template<typename Lexer>
-static Vector<String> parse_private_use_extensions(Lexer& lexer)
+static Vector<Utf16String> parse_private_use_extensions(Lexer& lexer)
 {
     // https://unicode.org/reports/tr35/#pu_extensions
     //
@@ -490,7 +485,7 @@ static Vector<String> parse_private_use_extensions(Lexer& lexer)
         return {};
 
     auto parse_values = [&]() {
-        Vector<String> extensions;
+        Vector<Utf16String> extensions;
 
         while (true) {
             auto segment = consume_next_segment(lexer);
@@ -502,7 +497,7 @@ static Vector<String> parse_private_use_extensions(Lexer& lexer)
                 break;
             }
 
-            extensions.append(string_from_ascii_view(*segment));
+            extensions.append(utf16_string_from_ascii_view(*segment));
         }
 
         return extensions;
@@ -582,22 +577,24 @@ Optional<LocaleID> parse_unicode_locale_id(Utf16View locale)
     return parse_unicode_locale_id_from_lexer(lexer);
 }
 
-String canonicalize_unicode_locale_id(StringView locale)
+Utf16String canonicalize_unicode_locale_id(StringView locale)
 {
     return LocaleData::canonicalize(locale);
 }
 
-String canonicalize_unicode_locale_id(Utf16View locale)
+Utf16String canonicalize_unicode_locale_id(Utf16View locale)
 {
-    return LocaleData::canonicalize(string_from_ascii_view(locale));
+    return LocaleData::canonicalize(locale.bytes());
 }
 
-String canonicalize_unicode_extension_values(StringView key, StringView value)
+Utf16String canonicalize_unicode_extension_values(StringView key, Utf16View value)
 {
+    VERIFY(value.has_ascii_storage());
+
     UErrorCode status = U_ZERO_ERROR;
 
     icu::LocaleBuilder builder;
-    builder.setUnicodeLocaleKeyword(icu_string_piece(key), icu_string_piece(value));
+    builder.setUnicodeLocaleKeyword(icu_string_piece(key), icu_string_piece(value.bytes()));
 
     auto locale = builder.build(status);
     verify_icu_success(status);
@@ -605,12 +602,12 @@ String canonicalize_unicode_extension_values(StringView key, StringView value)
     auto result = locale.getUnicodeKeywordValue<StringBuilder>(icu_string_piece(key), status);
     verify_icu_success(status);
 
-    return MUST(result.to_string());
+    return Utf16String::from_ascii_without_validation(result.string_view().bytes());
 }
 
-StringView default_locale()
+Utf16View default_locale()
 {
-    return "en"sv;
+    return Utf16View { "en"sv };
 }
 
 static void define_locales_without_scripts(HashTable<String>& locales)
@@ -687,15 +684,15 @@ Style style_from_string(Utf16View style)
     VERIFY_NOT_REACHED();
 }
 
-StringView style_to_string(Style style)
+Utf16String style_to_string(Style style)
 {
     switch (style) {
     case Style::Narrow:
-        return "narrow"sv;
+        return "narrow"_utf16;
     case Style::Short:
-        return "short"sv;
+        return "short"_utf16;
     case Style::Long:
-        return "long"sv;
+        return "long"_utf16;
     default:
         VERIFY_NOT_REACHED();
     }
@@ -716,7 +713,7 @@ static void apply_extensions_to_locale(icu::Locale& locale, icu::Locale const& l
     verify_icu_success(status);
 }
 
-Optional<String> add_likely_subtags(StringView locale)
+Optional<Utf16String> add_likely_subtags(StringView locale)
 {
     UErrorCode status = U_ZERO_ERROR;
 
@@ -740,10 +737,10 @@ Optional<String> add_likely_subtags(StringView locale)
     if (icu_failure(status))
         return {};
 
-    return MUST(result.to_string());
+    return Utf16String::from_ascii_without_validation(result.string_view().bytes());
 }
 
-Optional<String> remove_likely_subtags(StringView locale)
+Optional<Utf16String> remove_likely_subtags(StringView locale)
 {
     UErrorCode status = U_ZERO_ERROR;
 
@@ -767,57 +764,93 @@ Optional<String> remove_likely_subtags(StringView locale)
     if (icu_failure(status))
         return {};
 
-    return MUST(result.to_string());
+    return Utf16String::from_ascii_without_validation(result.string_view().bytes());
 }
 
-bool is_locale_character_ordering_right_to_left(StringView locale)
+bool is_locale_character_ordering_right_to_left(Utf16View locale)
 {
-    auto locale_data = LocaleData::for_locale(locale);
+    auto locale_data = LocaleData::for_locale(locale.bytes());
     if (!locale_data.has_value())
         return false; // Default to left-to-right
 
     return static_cast<bool>(locale_data->locale().isRightToLeft());
 }
 
+static void append_to_builder(StringBuilder& builder, StringView string)
+{
+    builder.append(string);
+}
+
+static void append_to_builder(Utf16StringBuilder& builder, StringView string)
+{
+    builder.append_ascii(string);
+}
+
+static void append_to_builder(StringBuilder& builder, Utf16String const& string)
+{
+    builder.append(string.utf16_view());
+}
+
+static void append_to_builder(Utf16StringBuilder& builder, Utf16String const& string)
+{
+    builder.append(string.utf16_view());
+}
+
+template<typename Builder>
+static void append_language_id_to_builder(Builder& builder, LanguageID const& language_id)
+{
+    auto append_segment = [&](Utf16String const& segment) {
+        if (!builder.is_empty())
+            append_to_builder(builder, "-"sv);
+        append_to_builder(builder, segment);
+    };
+
+    auto append_optional_segment = [&](Optional<Utf16String> const& segment) {
+        if (!segment.has_value())
+            return;
+        append_segment(*segment);
+    };
+
+    append_optional_segment(language_id.language);
+    append_optional_segment(language_id.script);
+    append_optional_segment(language_id.region);
+    for (auto const& variant : language_id.variants)
+        append_segment(variant);
+}
+
 String LanguageID::to_string() const
 {
     StringBuilder builder;
-
-    auto append_segment = [&](Optional<String> const& segment) {
-        if (!segment.has_value())
-            return;
-        if (!builder.is_empty())
-            builder.append('-');
-        builder.append(*segment);
-    };
-
-    append_segment(language);
-    append_segment(script);
-    append_segment(region);
-    for (auto const& variant : variants)
-        append_segment(variant);
+    append_language_id_to_builder(builder, *this);
 
     return MUST(builder.to_string());
 }
 
-String LocaleID::to_string() const
+Utf16String LanguageID::to_utf16_string() const
 {
-    StringBuilder builder;
+    Utf16StringBuilder builder;
+    append_language_id_to_builder(builder, *this);
 
+    return builder.to_string();
+}
+
+template<typename Builder>
+static void append_locale_id_to_builder(Builder& builder, LocaleID const& locale_id)
+{
     auto append_segment = [&](auto const& segment) {
         if (segment.is_empty())
             return;
         if (!builder.is_empty())
-            builder.append('-');
-        builder.append(segment);
+            append_to_builder(builder, "-"sv);
+        append_to_builder(builder, segment);
     };
 
-    append_segment(language_id.to_string());
+    append_language_id_to_builder(builder, locale_id.language_id);
 
-    for (auto const& extension : extensions) {
+    for (auto const& extension : locale_id.extensions) {
         extension.visit(
             [&](LocaleExtension const& ext) {
-                builder.append("-u"sv);
+                append_to_builder(builder, "-u"sv);
                 for (auto const& attribute : ext.attributes)
                     append_segment(attribute);
                 for (auto const& keyword : ext.keywords) {
@@ -826,27 +859,42 @@ String LocaleID::to_string() const
                 }
             },
             [&](TransformedExtension const& ext) {
-                builder.append("-t"sv);
+                append_to_builder(builder, "-t"sv);
                 if (ext.language.has_value())
-                    append_segment(ext.language->to_string());
+                    append_language_id_to_builder(builder, *ext.language);
                 for (auto const& field : ext.fields) {
                     append_segment(field.key);
                     append_segment(field.value);
                 }
             },
             [&](OtherExtension const& ext) {
-                builder.appendff("-{}", ext.key);
+                append_to_builder(builder, "-"sv);
+                builder.append_code_unit(ext.key);
                 append_segment(ext.value);
             });
     }
 
-    if (!private_use_extensions.is_empty()) {
-        builder.append("-x"sv);
-        for (auto const& extension : private_use_extensions)
+    if (!locale_id.private_use_extensions.is_empty()) {
+        append_to_builder(builder, "-x"sv);
+        for (auto const& extension : locale_id.private_use_extensions)
             append_segment(extension);
     }
+}
+
+String LocaleID::to_string() const
+{
+    StringBuilder builder;
+    append_locale_id_to_builder(builder, *this);
 
     return MUST(builder.to_string());
 }
 
+Utf16String LocaleID::to_utf16_string() const
+{
+    Utf16StringBuilder builder;
+    append_locale_id_to_builder(builder, *this);
+
+    return builder.to_string();
+}
+
 }
diff --git a/Libraries/LibUnicode/Locale.h b/Libraries/LibUnicode/Locale.h
index 0ba404a1e3..47d24c4a54 100644
--- a/Libraries/LibUnicode/Locale.h
+++ b/Libraries/LibUnicode/Locale.h
@@ -11,6 +11,7 @@
 #include <AK/Optional.h>
 #include <AK/String.h>
 #include <AK/StringView.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 #include <AK/Variant.h>
 #include <AK/Vector.h>
@@ -20,28 +21,29 @@ namespace Unicode {
 
 struct LanguageID {
     String to_string() const;
+    Utf16String to_utf16_string() const;
     bool operator==(LanguageID const&) const = default;
 
     bool is_root { false };
-    Optional<String> language {};
-    Optional<String> script {};
-    Optional<String> region {};
-    Vector<String> variants {};
+    Optional<Utf16String> language {};
+    Optional<Utf16String> script {};
+    Optional<Utf16String> region {};
+    Vector<Utf16String> variants {};
 };
 
 struct Keyword {
-    String key {};
-    String value {};
+    Utf16String key {};
+    Utf16String value {};
 };
 
 struct LocaleExtension {
-    Vector<String> attributes {};
+    Vector<Utf16String> attributes {};
     Vector<Keyword> keywords {};
 };
 
 struct TransformedField {
-    String key {};
-    String value {};
+    Utf16String key {};
+    Utf16String value {};
 };
 
 struct TransformedExtension {
@@ -51,13 +53,14 @@ struct TransformedExtension {
 
 struct OtherExtension {
     char key {};
-    String value {};
+    Utf16String value {};
 };
 
 using Extension = AK::Variant<LocaleExtension, TransformedExtension, OtherExtension>;
 
 struct LocaleID {
     String to_string() const;
+    Utf16String to_utf16_string() const;
 
     template<typename ExtensionType>
     Vector<Extension> remove_extension_type()
@@ -88,7 +91,7 @@ struct LocaleID {
 
     LanguageID language_id {};
     Vector<Extension> extensions {};
-    Vector<String> private_use_extensions {};
+    Vector<Utf16String> private_use_extensions {};
 };
 
 enum class Style {
@@ -179,20 +182,20 @@ Optional<LanguageID> parse_unicode_language_id(Utf16View);
 Optional<LocaleID> parse_unicode_locale_id(StringView);
 Optional<LocaleID> parse_unicode_locale_id(Utf16View);
 
-String canonicalize_unicode_locale_id(StringView);
-String canonicalize_unicode_locale_id(Utf16View);
-String canonicalize_unicode_extension_values(StringView key, StringView value);
+Utf16String canonicalize_unicode_locale_id(StringView);
+Utf16String canonicalize_unicode_locale_id(Utf16View);
+Utf16String canonicalize_unicode_extension_values(StringView key, Utf16View value);
 
-StringView default_locale();
+Utf16View default_locale();
 bool is_locale_available(StringView locale);
 
 Style style_from_string(StringView style);
 Style style_from_string(Utf16View style);
-StringView style_to_string(Style style);
+Utf16String style_to_string(Style style);
 
-Optional<String> add_likely_subtags(StringView);
-Optional<String> remove_likely_subtags(StringView);
+Optional<Utf16String> add_likely_subtags(StringView);
+Optional<Utf16String> remove_likely_subtags(StringView);
 
-bool is_locale_character_ordering_right_to_left(StringView locale);
+bool is_locale_character_ordering_right_to_left(Utf16View locale);
 
 }
diff --git a/Libraries/LibUnicode/Normalize.cpp b/Libraries/LibUnicode/Normalize.cpp
index 4bf943abd7..d290d23abb 100644
--- a/Libraries/LibUnicode/Normalize.cpp
+++ b/Libraries/LibUnicode/Normalize.cpp
@@ -39,21 +39,6 @@ NormalizationForm normalization_form_from_string(Utf16View form)
     VERIFY_NOT_REACHED();
 }
 
-StringView normalization_form_to_string(NormalizationForm form)
-{
-    switch (form) {
-    case NormalizationForm::NFD:
-        return "NFD"sv;
-    case NormalizationForm::NFC:
-        return "NFC"sv;
-    case NormalizationForm::NFKD:
-        return "NFKD"sv;
-    case NormalizationForm::NFKC:
-        return "NFKC"sv;
-    }
-    VERIFY_NOT_REACHED();
-}
-
 static icu::Normalizer2 const* normalizer_for_form(NormalizationForm form, UErrorCode& status)
 {
     switch (form) {
diff --git a/Libraries/LibUnicode/Normalize.h b/Libraries/LibUnicode/Normalize.h
index b9c33885a0..5951414441 100644
--- a/Libraries/LibUnicode/Normalize.h
+++ b/Libraries/LibUnicode/Normalize.h
@@ -22,7 +22,6 @@ enum class NormalizationForm {
 };
 NormalizationForm normalization_form_from_string(StringView);
 NormalizationForm normalization_form_from_string(Utf16View);
-StringView normalization_form_to_string(NormalizationForm);
 
 String normalize(StringView string, NormalizationForm form);
 Utf16String normalize(Utf16View string, NormalizationForm form);
diff --git a/Libraries/LibUnicode/NumberFormat.cpp b/Libraries/LibUnicode/NumberFormat.cpp
index d8b48d9ebd..b84157c153 100644
--- a/Libraries/LibUnicode/NumberFormat.cpp
+++ b/Libraries/LibUnicode/NumberFormat.cpp
@@ -44,17 +44,17 @@ NumberFormatStyle number_format_style_from_string(Utf16View number_format_style)
     VERIFY_NOT_REACHED();
 }
 
-StringView number_format_style_to_string(NumberFormatStyle number_format_style)
+Utf16String number_format_style_to_string(NumberFormatStyle number_format_style)
 {
     switch (number_format_style) {
     case NumberFormatStyle::Decimal:
-        return "decimal"sv;
+        return "decimal"_utf16;
     case NumberFormatStyle::Percent:
-        return "percent"sv;
+        return "percent"_utf16;
     case NumberFormatStyle::Currency:
-        return "currency"sv;
+        return "currency"_utf16;
     case NumberFormatStyle::Unit:
-        return "unit"sv;
+        return "unit"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -89,19 +89,19 @@ SignDisplay sign_display_from_string(Utf16View sign_display)
     VERIFY_NOT_REACHED();
 }
 
-StringView sign_display_to_string(SignDisplay sign_display)
+Utf16String sign_display_to_string(SignDisplay sign_display)
 {
     switch (sign_display) {
     case SignDisplay::Auto:
-        return "auto"sv;
+        return "auto"_utf16;
     case SignDisplay::Never:
-        return "never"sv;
+        return "never"_utf16;
     case SignDisplay::Always:
-        return "always"sv;
+        return "always"_utf16;
     case SignDisplay::ExceptZero:
-        return "exceptZero"sv;
+        return "exceptZero"_utf16;
     case SignDisplay::Negative:
-        return "negative"sv;
+        return "negative"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -149,17 +149,17 @@ Notation notation_from_string(Utf16View notation)
     VERIFY_NOT_REACHED();
 }
 
-StringView notation_to_string(Notation notation)
+Utf16String notation_to_string(Notation notation)
 {
     switch (notation) {
     case Notation::Standard:
-        return "standard"sv;
+        return "standard"_utf16;
     case Notation::Scientific:
-        return "scientific"sv;
+        return "scientific"_utf16;
     case Notation::Engineering:
-        return "engineering"sv;
+        return "engineering"_utf16;
     case Notation::Compact:
-        return "compact"sv;
+        return "compact"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -202,13 +202,13 @@ CompactDisplay compact_display_from_string(Utf16View compact_display)
     VERIFY_NOT_REACHED();
 }
 
-StringView compact_display_to_string(CompactDisplay compact_display)
+Utf16String compact_display_to_string(CompactDisplay compact_display)
 {
     switch (compact_display) {
     case CompactDisplay::Short:
-        return "short"sv;
+        return "short"_utf16;
     case CompactDisplay::Long:
-        return "long"sv;
+        return "long"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -226,17 +226,17 @@ Grouping grouping_from_string(StringView grouping)
     VERIFY_NOT_REACHED();
 }
 
-StringView grouping_to_string(Grouping grouping)
+Utf16String grouping_to_string(Grouping grouping)
 {
     switch (grouping) {
     case Grouping::Always:
-        return "always"sv;
+        return "always"_utf16;
     case Grouping::Auto:
-        return "auto"sv;
+        return "auto"_utf16;
     case Grouping::Min2:
-        return "min2"sv;
+        return "min2"_utf16;
     case Grouping::False:
-        return "false"sv;
+        return "false"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -282,17 +282,17 @@ CurrencyDisplay currency_display_from_string(Utf16View currency_display)
     VERIFY_NOT_REACHED();
 }
 
-StringView currency_display_to_string(CurrencyDisplay currency_display)
+Utf16String currency_display_to_string(CurrencyDisplay currency_display)
 {
     switch (currency_display) {
     case CurrencyDisplay::Code:
-        return "code"sv;
+        return "code"_utf16;
     case CurrencyDisplay::Symbol:
-        return "symbol"sv;
+        return "symbol"_utf16;
     case CurrencyDisplay::NarrowSymbol:
-        return "narrowSymbol"sv;
+        return "narrowSymbol"_utf16;
     case CurrencyDisplay::Name:
-        return "name"sv;
+        return "name"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -330,13 +330,13 @@ CurrencySign currency_sign_from_string(Utf16View currency_sign)
     VERIFY_NOT_REACHED();
 }
 
-StringView currency_sign_to_string(CurrencySign currency_sign)
+Utf16String currency_sign_to_string(CurrencySign currency_sign)
 {
     switch (currency_sign) {
     case CurrencySign::Standard:
-        return "standard"sv;
+        return "standard"_utf16;
     case CurrencySign::Accounting:
-        return "accounting"sv;
+        return "accounting"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -354,17 +354,17 @@ RoundingType rounding_type_from_string(StringView rounding_type)
     VERIFY_NOT_REACHED();
 }
 
-StringView rounding_type_to_string(RoundingType rounding_type)
+Utf16String rounding_type_to_string(RoundingType rounding_type)
 {
     switch (rounding_type) {
     case RoundingType::SignificantDigits:
-        return "significantDigits"sv;
+        return "significantDigits"_utf16;
     case RoundingType::FractionDigits:
-        return "fractionDigits"sv;
+        return "fractionDigits"_utf16;
     case RoundingType::MorePrecision:
-        return "morePrecision"sv;
+        return "morePrecision"_utf16;
     case RoundingType::LessPrecision:
-        return "lessPrecision"sv;
+        return "lessPrecision"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -415,27 +415,27 @@ RoundingMode rounding_mode_from_string(Utf16View rounding_mode)
     VERIFY_NOT_REACHED();
 }
 
-StringView rounding_mode_to_string(RoundingMode rounding_mode)
+Utf16String rounding_mode_to_string(RoundingMode rounding_mode)
 {
     switch (rounding_mode) {
     case RoundingMode::Ceil:
-        return "ceil"sv;
+        return "ceil"_utf16;
     case RoundingMode::Expand:
-        return "expand"sv;
+        return "expand"_utf16;
     case RoundingMode::Floor:
-        return "floor"sv;
+        return "floor"_utf16;
     case RoundingMode::HalfCeil:
-        return "halfCeil"sv;
+        return "halfCeil"_utf16;
     case RoundingMode::HalfEven:
-        return "halfEven"sv;
+        return "halfEven"_utf16;
     case RoundingMode::HalfExpand:
-        return "halfExpand"sv;
+        return "halfExpand"_utf16;
     case RoundingMode::HalfFloor:
-        return "halfFloor"sv;
+        return "halfFloor"_utf16;
     case RoundingMode::HalfTrunc:
-        return "halfTrunc"sv;
+        return "halfTrunc"_utf16;
     case RoundingMode::Trunc:
-        return "trunc"sv;
+        return "trunc"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -483,13 +483,13 @@ TrailingZeroDisplay trailing_zero_display_from_string(Utf16View trailing_zero_di
     VERIFY_NOT_REACHED();
 }
 
-StringView trailing_zero_display_to_string(TrailingZeroDisplay trailing_zero_display)
+Utf16String trailing_zero_display_to_string(TrailingZeroDisplay trailing_zero_display)
 {
     switch (trailing_zero_display) {
     case TrailingZeroDisplay::Auto:
-        return "auto"sv;
+        return "auto"_utf16;
     case TrailingZeroDisplay::StripIfInteger:
-        return "stripIfInteger"sv;
+        return "stripIfInteger"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -541,14 +541,23 @@ static void apply_display_options(icu::number::LocalizedNumberFormatter& formatt
         formatter = formatter.unit(icu::MeasureUnit::getPercent()).scale(icu::number::Scale::byDouble(100));
         break;
 
-    case NumberFormatStyle::Currency:
-        formatter = formatter.unit(icu::CurrencyUnit(icu_string_piece(*display_options.currency), status));
+    case NumberFormatStyle::Currency: {
+        VERIFY(display_options.currency->length_in_code_units() == 3);
+        UChar currency_code[4] {
+            display_options.currency->code_unit_at(0),
+            display_options.currency->code_unit_at(1),
+            display_options.currency->code_unit_at(2),
+            0,
+        };
+        formatter = formatter.unit(icu::CurrencyUnit(currency_code, status));
         formatter = formatter.unitWidth(icu_currency_display(*display_options.currency_display));
         verify_icu_success(status);
         break;
+    }
 
     case NumberFormatStyle::Unit:
-        formatter = formatter.unit(icu::MeasureUnit::forIdentifier(icu_string_piece(*display_options.unit), status));
+        auto unit = display_options.unit->to_utf8();
+        formatter = formatter.unit(icu::MeasureUnit::forIdentifier(icu_string_piece(unit.bytes_as_string_view()), status));
         formatter = formatter.unitWidth(icu_unit_width(*display_options.unit_display));
         verify_icu_success(status);
         break;
@@ -593,47 +602,47 @@ static void apply_rounding_options(icu::number::LocalizedNumberFormatter& format
     formatter = formatter.roundingMode(icu_rounding_mode(rounding_options.mode));
 }
 
-static constexpr StringView icu_number_format_field_to_string(i32 field, NumberFormat::Value const& value, bool is_unit)
+static Utf16String icu_number_format_field_to_string(i32 field, NumberFormat::Value const& value, bool is_unit)
 {
     switch (field) {
     case PartitionRange::LITERAL_FIELD:
-        return "literal"sv;
+        return "literal"_utf16;
     case UNUM_INTEGER_FIELD:
         if (auto const* number = value.get_pointer<double>()) {
             if (isnan(*number))
-                return "nan"sv;
+                return "nan"_utf16;
             if (isinf(*number))
-                return "infinity"sv;
+                return "infinity"_utf16;
         }
-        return "integer"sv;
+        return "integer"_utf16;
     case UNUM_FRACTION_FIELD:
-        return "fraction"sv;
+        return "fraction"_utf16;
     case UNUM_DECIMAL_SEPARATOR_FIELD:
-        return "decimal"sv;
+        return "decimal"_utf16;
     case UNUM_EXPONENT_SYMBOL_FIELD:
-        return "exponentSeparator"sv;
+        return "exponentSeparator"_utf16;
     case UNUM_EXPONENT_SIGN_FIELD:
-        return "exponentMinusSign"sv;
+        return "exponentMinusSign"_utf16;
     case UNUM_EXPONENT_FIELD:
-        return "exponentInteger"sv;
+        return "exponentInteger"_utf16;
     case UNUM_GROUPING_SEPARATOR_FIELD:
-        return "group"sv;
+        return "group"_utf16;
     case UNUM_CURRENCY_FIELD:
-        return "currency"sv;
+        return "currency"_utf16;
     case UNUM_PERCENT_FIELD:
-        return is_unit ? "unit"sv : "percentSign"sv;
+        return is_unit ? "unit"_utf16 : "percentSign"_utf16;
     case UNUM_SIGN_FIELD: {
         auto is_negative = value.visit(
             [&](double number) { return signbit(number); },
             [&](Utf16String const& number) { return number.starts_with('-'); });
-        return is_negative ? "minusSign"sv : "plusSign"sv;
+        return is_negative ? "minusSign"_utf16 : "plusSign"_utf16;
     }
     case UNUM_MEASURE_UNIT_FIELD:
-        return "unit"sv;
+        return "unit"_utf16;
     case UNUM_COMPACT_FIELD:
-        return "compact"sv;
+        return "compact"_utf16;
     case UNUM_APPROXIMATELY_SIGN_FIELD:
-        return "approximatelySign"sv;
+        return "approximatelySign"_utf16;
     }
 
     VERIFY_NOT_REACHED();
@@ -936,18 +945,18 @@ private:
         auto apply_to_partition = [&](Partition& partition, auto field, auto index) {
             if (start_range.has_value() && start_range->contains(index)) {
                 partition.type = icu_number_format_field_to_string(field, start, m_is_unit);
-                partition.source = "startRange"sv;
+                partition.source = "startRange"_utf16;
                 return;
             }
 
             if (end_range.has_value() && end_range->contains(index)) {
                 partition.type = icu_number_format_field_to_string(field, end, m_is_unit);
-                partition.source = "endRange"sv;
+                partition.source = "endRange"_utf16;
                 return;
             }
 
             partition.type = icu_number_format_field_to_string(field, end, m_is_unit);
-            partition.source = "shared"sv;
+            partition.source = "shared"_utf16;
         };
 
         Vector<Partition> result;
diff --git a/Libraries/LibUnicode/NumberFormat.h b/Libraries/LibUnicode/NumberFormat.h
index fff34b7629..7b1b6e1471 100644
--- a/Libraries/LibUnicode/NumberFormat.h
+++ b/Libraries/LibUnicode/NumberFormat.h
@@ -26,7 +26,7 @@ enum class NumberFormatStyle {
 };
 NumberFormatStyle number_format_style_from_string(StringView);
 NumberFormatStyle number_format_style_from_string(Utf16View);
-StringView number_format_style_to_string(NumberFormatStyle);
+Utf16String number_format_style_to_string(NumberFormatStyle);
 
 enum class SignDisplay {
     Auto,
@@ -37,7 +37,7 @@ enum class SignDisplay {
 };
 SignDisplay sign_display_from_string(StringView);
 SignDisplay sign_display_from_string(Utf16View);
-StringView sign_display_to_string(SignDisplay);
+Utf16String sign_display_to_string(SignDisplay);
 
 enum class Notation {
     Standard,
@@ -47,7 +47,7 @@ enum class Notation {
 };
 Notation notation_from_string(StringView);
 Notation notation_from_string(Utf16View);
-StringView notation_to_string(Notation);
+Utf16String notation_to_string(Notation);
 
 enum class CompactDisplay {
     Short,
@@ -55,7 +55,7 @@ enum class CompactDisplay {
 };
 CompactDisplay compact_display_from_string(StringView);
 CompactDisplay compact_display_from_string(Utf16View);
-StringView compact_display_to_string(CompactDisplay);
+Utf16String compact_display_to_string(CompactDisplay);
 
 enum class Grouping {
     Always,
@@ -64,7 +64,7 @@ enum class Grouping {
     False,
 };
 Grouping grouping_from_string(StringView);
-StringView grouping_to_string(Grouping);
+Utf16String grouping_to_string(Grouping);
 
 enum class CurrencyDisplay {
     Code,
@@ -74,7 +74,7 @@ enum class CurrencyDisplay {
 };
 CurrencyDisplay currency_display_from_string(StringView);
 CurrencyDisplay currency_display_from_string(Utf16View);
-StringView currency_display_to_string(CurrencyDisplay);
+Utf16String currency_display_to_string(CurrencyDisplay);
 
 enum class CurrencySign {
     Standard,
@@ -82,7 +82,7 @@ enum class CurrencySign {
 };
 CurrencySign currency_sign_from_string(StringView);
 CurrencySign currency_sign_from_string(Utf16View);
-StringView currency_sign_to_string(CurrencySign);
+Utf16String currency_sign_to_string(CurrencySign);
 
 struct DisplayOptions {
     NumberFormatStyle style { NumberFormatStyle::Decimal };
@@ -93,11 +93,11 @@ struct DisplayOptions {
 
     Grouping grouping { Grouping::Always };
 
-    Optional<String> currency;
+    Optional<Utf16String> currency;
     Optional<CurrencyDisplay> currency_display;
     Optional<CurrencySign> currency_sign;
 
-    Optional<String> unit;
+    Optional<Utf16String> unit;
     Optional<Style> unit_display;
 };
 
@@ -108,7 +108,7 @@ enum class RoundingType {
     LessPrecision,
 };
 RoundingType rounding_type_from_string(StringView);
-StringView rounding_type_to_string(RoundingType);
+Utf16String rounding_type_to_string(RoundingType);
 
 enum class RoundingMode {
     Ceil,
@@ -123,7 +123,7 @@ enum class RoundingMode {
 };
 RoundingMode rounding_mode_from_string(StringView);
 RoundingMode rounding_mode_from_string(Utf16View);
-StringView rounding_mode_to_string(RoundingMode);
+Utf16String rounding_mode_to_string(RoundingMode);
 
 enum class TrailingZeroDisplay {
     Auto,
@@ -131,7 +131,7 @@ enum class TrailingZeroDisplay {
 };
 TrailingZeroDisplay trailing_zero_display_from_string(StringView);
 TrailingZeroDisplay trailing_zero_display_from_string(Utf16View);
-StringView trailing_zero_display_to_string(TrailingZeroDisplay);
+Utf16String trailing_zero_display_to_string(TrailingZeroDisplay);
 
 struct RoundingOptions {
     RoundingType type { RoundingType::MorePrecision };
@@ -158,9 +158,9 @@ public:
     virtual ~NumberFormat() = default;
 
     struct Partition {
-        StringView type;
+        Utf16String type;
         Utf16String value;
-        StringView source;
+        Utf16String source;
     };
 
     using Value = Variant<double, Utf16String>;
diff --git a/Libraries/LibUnicode/PluralRules.cpp b/Libraries/LibUnicode/PluralRules.cpp
index 444d30dc70..bc11226637 100644
--- a/Libraries/LibUnicode/PluralRules.cpp
+++ b/Libraries/LibUnicode/PluralRules.cpp
@@ -26,13 +26,13 @@ PluralForm plural_form_from_string(Utf16View plural_form)
     VERIFY_NOT_REACHED();
 }
 
-StringView plural_form_to_string(PluralForm plural_form)
+Utf16String plural_form_to_string(PluralForm plural_form)
 {
     switch (plural_form) {
     case PluralForm::Cardinal:
-        return "cardinal"sv;
+        return "cardinal"_utf16;
     case PluralForm::Ordinal:
-        return "ordinal"sv;
+        return "ordinal"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
diff --git a/Libraries/LibUnicode/PluralRules.h b/Libraries/LibUnicode/PluralRules.h
index ba1ef24a1a..49027802d3 100644
--- a/Libraries/LibUnicode/PluralRules.h
+++ b/Libraries/LibUnicode/PluralRules.h
@@ -7,6 +7,7 @@
 #pragma once
 
 #include <AK/StringView.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 
 namespace Unicode {
@@ -17,7 +18,7 @@ enum class PluralForm {
 };
 PluralForm plural_form_from_string(StringView);
 PluralForm plural_form_from_string(Utf16View);
-StringView plural_form_to_string(PluralForm);
+Utf16String plural_form_to_string(PluralForm);
 
 enum class PluralCategory {
     // NOTE: These are sorted in preferred order for Intl.PluralRules.prototype.resolvedOptions.
diff --git a/Libraries/LibUnicode/RelativeTimeFormat.cpp b/Libraries/LibUnicode/RelativeTimeFormat.cpp
index 51bb0f9b6c..1e192aeb92 100644
--- a/Libraries/LibUnicode/RelativeTimeFormat.cpp
+++ b/Libraries/LibUnicode/RelativeTimeFormat.cpp
@@ -58,25 +58,25 @@ Optional<TimeUnit> time_unit_from_string(Utf16View time_unit)
     return {};
 }
 
-StringView time_unit_to_string(TimeUnit time_unit)
+Utf16String time_unit_to_string(TimeUnit time_unit)
 {
     switch (time_unit) {
     case TimeUnit::Second:
-        return "second"sv;
+        return "second"_utf16;
     case TimeUnit::Minute:
-        return "minute"sv;
+        return "minute"_utf16;
     case TimeUnit::Hour:
-        return "hour"sv;
+        return "hour"_utf16;
     case TimeUnit::Day:
-        return "day"sv;
+        return "day"_utf16;
     case TimeUnit::Week:
-        return "week"sv;
+        return "week"_utf16;
     case TimeUnit::Month:
-        return "month"sv;
+        return "month"_utf16;
     case TimeUnit::Quarter:
-        return "quarter"sv;
+        return "quarter"_utf16;
     case TimeUnit::Year:
-        return "year"sv;
+        return "year"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -122,13 +122,13 @@ NumericDisplay numeric_display_from_string(Utf16View numeric_display)
     VERIFY_NOT_REACHED();
 }
 
-StringView numeric_display_to_string(NumericDisplay numeric_display)
+Utf16String numeric_display_to_string(NumericDisplay numeric_display)
 {
     switch (numeric_display) {
     case NumericDisplay::Always:
-        return "always"sv;
+        return "always"_utf16;
     case NumericDisplay::Auto:
-        return "auto"sv;
+        return "auto"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -146,19 +146,19 @@ static constexpr UDateRelativeDateTimeFormatterStyle icu_relative_date_time_styl
     VERIFY_NOT_REACHED();
 }
 
-static constexpr StringView icu_relative_time_format_field_to_string(i32 field)
+static Utf16String icu_relative_time_format_field_to_string(i32 field)
 {
     switch (field) {
     case PartitionRange::LITERAL_FIELD:
-        return "literal"sv;
+        return "literal"_utf16;
     case UNUM_INTEGER_FIELD:
-        return "integer"sv;
+        return "integer"_utf16;
     case UNUM_FRACTION_FIELD:
-        return "fraction"sv;
+        return "fraction"_utf16;
     case UNUM_DECIMAL_SEPARATOR_FIELD:
-        return "decimal"sv;
+        return "decimal"_utf16;
     case UNUM_GROUPING_SEPARATOR_FIELD:
-        return "group"sv;
+        return "group"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
diff --git a/Libraries/LibUnicode/RelativeTimeFormat.h b/Libraries/LibUnicode/RelativeTimeFormat.h
index f538ca8e0c..490a1622e9 100644
--- a/Libraries/LibUnicode/RelativeTimeFormat.h
+++ b/Libraries/LibUnicode/RelativeTimeFormat.h
@@ -30,7 +30,7 @@ enum class TimeUnit {
 };
 Optional<TimeUnit> time_unit_from_string(StringView);
 Optional<TimeUnit> time_unit_from_string(Utf16View);
-StringView time_unit_to_string(TimeUnit);
+Utf16String time_unit_to_string(TimeUnit);
 
 enum class NumericDisplay {
     Always,
@@ -38,7 +38,7 @@ enum class NumericDisplay {
 };
 NumericDisplay numeric_display_from_string(StringView);
 NumericDisplay numeric_display_from_string(Utf16View);
-StringView numeric_display_to_string(NumericDisplay);
+Utf16String numeric_display_to_string(NumericDisplay);
 
 class RelativeTimeFormat {
 public:
@@ -46,9 +46,9 @@ public:
     virtual ~RelativeTimeFormat() = default;
 
     struct Partition {
-        StringView type;
+        Utf16String type;
         Utf16String value;
-        StringView unit;
+        Utf16String unit;
     };
 
     virtual Utf16String format(double, TimeUnit, NumericDisplay) const = 0;
diff --git a/Libraries/LibUnicode/Segmenter.cpp b/Libraries/LibUnicode/Segmenter.cpp
index 41829c20f8..71ab2cca45 100644
--- a/Libraries/LibUnicode/Segmenter.cpp
+++ b/Libraries/LibUnicode/Segmenter.cpp
@@ -45,17 +45,17 @@ SegmenterGranularity segmenter_granularity_from_string(Utf16View segmenter_granu
     VERIFY_NOT_REACHED();
 }
 
-StringView segmenter_granularity_to_string(SegmenterGranularity segmenter_granularity)
+Utf16String segmenter_granularity_to_string(SegmenterGranularity segmenter_granularity)
 {
     switch (segmenter_granularity) {
     case SegmenterGranularity::Grapheme:
-        return "grapheme"sv;
+        return "grapheme"_utf16;
     case SegmenterGranularity::Line:
-        return "line"sv;
+        return "line"_utf16;
     case SegmenterGranularity::Sentence:
-        return "sentence"sv;
+        return "sentence"_utf16;
     case SegmenterGranularity::Word:
-        return "word"sv;
+        return "word"_utf16;
     }
     VERIFY_NOT_REACHED();
 }
@@ -688,7 +688,7 @@ private:
 
 NonnullOwnPtr<Segmenter> Segmenter::create(SegmenterGranularity segmenter_granularity)
 {
-    return Segmenter::create(default_locale(), segmenter_granularity);
+    return Segmenter::create(default_locale().bytes(), segmenter_granularity);
 }
 
 NonnullOwnPtr<Segmenter> Segmenter::create(StringView locale, SegmenterGranularity segmenter_granularity)
diff --git a/Libraries/LibUnicode/Segmenter.h b/Libraries/LibUnicode/Segmenter.h
index d9b85f122b..69d2a52092 100644
--- a/Libraries/LibUnicode/Segmenter.h
+++ b/Libraries/LibUnicode/Segmenter.h
@@ -11,6 +11,7 @@
 #include <AK/Optional.h>
 #include <AK/OwnPtr.h>
 #include <AK/StringView.h>
+#include <AK/Utf16String.h>
 #include <AK/Utf16View.h>
 
 namespace Unicode {
@@ -23,7 +24,7 @@ enum class SegmenterGranularity {
 };
 SegmenterGranularity segmenter_granularity_from_string(StringView);
 SegmenterGranularity segmenter_granularity_from_string(Utf16View);
-StringView segmenter_granularity_to_string(SegmenterGranularity);
+Utf16String segmenter_granularity_to_string(SegmenterGranularity);
 
 class Segmenter {
 public:
diff --git a/Libraries/LibUnicode/TimeZone.cpp b/Libraries/LibUnicode/TimeZone.cpp
index e6c7f2c4a1..09cf314b32 100644
--- a/Libraries/LibUnicode/TimeZone.cpp
+++ b/Libraries/LibUnicode/TimeZone.cpp
@@ -19,16 +19,16 @@ namespace Unicode {
 
 static auto& cached_system_time_zone()
 {
-    static NeverDestroyed<Optional<String>> cached_system_time_zone;
+    static NeverDestroyed<Optional<Utf16String>> cached_system_time_zone;
     return *cached_system_time_zone;
 }
 
-static String current_time_zone_impl(OwnPtr<icu::TimeZone> time_zone)
+static Utf16String current_time_zone_impl(OwnPtr<icu::TimeZone> time_zone)
 {
     UErrorCode status = U_ZERO_ERROR;
 
     if (!time_zone || *time_zone == icu::TimeZone::getUnknown())
-        return "UTC"_string;
+        return "UTC"_utf16;
 
     icu::UnicodeString time_zone_id;
     time_zone->getID(time_zone_id);
@@ -37,22 +37,22 @@ static String current_time_zone_impl(OwnPtr<icu::TimeZone> time_zone)
     time_zone->getCanonicalID(time_zone_id, time_zone_name, status);
 
     if (icu_failure(status))
-        return "UTC"_string;
+        return "UTC"_utf16;
 
-    return icu_string_to_string(time_zone_name);
+    return icu_string_to_utf16_string(time_zone_name);
 }
 
-static String current_host_time_zone()
+static Utf16String current_host_time_zone()
 {
     return current_time_zone_impl(adopt_own_if_nonnull(icu::TimeZone::detectHostTimeZone()));
 }
 
-static String current_default_time_zone()
+static Utf16String current_default_time_zone()
 {
     return current_time_zone_impl(adopt_own_if_nonnull(icu::TimeZone::createDefault()));
 }
 
-String current_time_zone()
+Utf16String current_time_zone()
 {
     return cached_system_time_zone().ensure([] { return current_host_time_zone(); });
 }
@@ -62,7 +62,7 @@ void clear_system_time_zone_cache()
     cached_system_time_zone().clear();
 }
 
-ErrorOr<void> set_current_time_zone(StringView time_zone)
+ErrorOr<void> set_current_time_zone(Utf16View time_zone)
 {
     auto time_zone_data = TimeZoneData::for_time_zone(time_zone);
     if (!time_zone_data.has_value())
@@ -113,36 +113,58 @@ static constexpr bool is_legacy_non_iana_time_zone(StringView time_zone)
     return legacy_zones.contains_slow(time_zone);
 }
 
-static Vector<String> icu_available_time_zones(Optional<ByteString> const& region)
+static Vector<Utf16String> icu_available_time_zones(Optional<StringView> region)
 {
     UErrorCode status = U_ZERO_ERROR;
 
-    char const* icu_region = region.has_value() ? region->characters() : nullptr;
+    Array<u8, 4> region_buffer {};
+    char const* icu_region = nullptr;
+    if (region.has_value()) {
+        VERIFY(region->length() < region_buffer.size());
+        region->bytes().copy_to(region_buffer.span());
+        icu_region = reinterpret_cast<char const*>(region_buffer.data());
+    }
 
     auto time_zone_enumerator = adopt_own_if_nonnull(icu::TimeZone::createTimeZoneIDEnumeration(UCAL_ZONE_TYPE_ANY, icu_region, nullptr, status));
     if (icu_failure(status))
-        return { "UTC"_string };
+        return { Utf16String::from_ascii_without_validation("UTC"sv.bytes()) };
 
-    auto time_zones = icu_string_enumeration_to_list(move(time_zone_enumerator), nullptr, [](char const* zone, size_t zone_length) {
-        return !is_legacy_non_iana_time_zone({ zone, zone_length });
-    });
+    Vector<Utf16String> time_zones;
+    while (true) {
+        i32 length = 0;
+        auto const* time_zone = time_zone_enumerator->next(&length, status);
+
+        if (icu_failure(status) || time_zone == nullptr)
+            break;
+
+        StringView time_zone_view { time_zone, static_cast<size_t>(length) };
+        if (!is_legacy_non_iana_time_zone(time_zone_view))
+            time_zones.append(Utf16String::from_ascii_without_validation(time_zone_view.bytes()));
+    }
 
     quick_sort(time_zones);
     return time_zones;
 }
 
-Vector<String> const& available_time_zones()
+Vector<Utf16String> const& available_time_zones()
 {
-    static NeverDestroyed<Vector<String>> time_zones { icu_available_time_zones({}) };
+    static NeverDestroyed<Vector<Utf16String>> time_zones { icu_available_time_zones({}) };
     return *time_zones;
 }
 
-Vector<String> available_time_zones_in_region(StringView region)
+Vector<Utf16String> available_time_zones_in_region(Utf16View region)
 {
-    return icu_available_time_zones(region);
+    VERIFY(region.length_in_code_units() < 4);
+    Array<char, 4> region_buffer {};
+    for (auto i = 0uz; i < region.length_in_code_units(); ++i) {
+        auto code_unit = region.code_unit_at(i);
+        VERIFY(code_unit <= 0x7f);
+        region_buffer[i] = static_cast<char>(code_unit);
+    }
+    return icu_available_time_zones(StringView { region_buffer.data(), region.length_in_code_units() });
 }
 
-Optional<String> resolve_primary_time_zone(StringView time_zone)
+Optional<Utf16String> resolve_primary_time_zone(StringView time_zone)
 {
     UErrorCode status = U_ZERO_ERROR;
 
@@ -152,7 +174,7 @@ Optional<String> resolve_primary_time_zone(StringView time_zone)
     if (icu_failure(status))
         return {};
 
-    return icu_string_to_string(iana_id);
+    return icu_string_to_utf16_string(iana_id);
 }
 
 static UDate to_icu_time(UnixDateTime time)
diff --git a/Libraries/LibUnicode/TimeZone.h b/Libraries/LibUnicode/TimeZone.h
index 0ce2bb5a51..16486dd3a7 100644
--- a/Libraries/LibUnicode/TimeZone.h
+++ b/Libraries/LibUnicode/TimeZone.h
@@ -10,6 +10,8 @@
 #include <AK/Optional.h>
 #include <AK/String.h>
 #include <AK/Time.h>
+#include <AK/Utf16String.h>
+#include <AK/Utf16View.h>
 #include <AK/Vector.h>
 
 namespace Unicode {
@@ -49,12 +51,12 @@ struct TimeZoneTransition {
     AK::Duration transition;
 };
 
-String current_time_zone();
-ErrorOr<void> set_current_time_zone(StringView);
+Utf16String current_time_zone();
+ErrorOr<void> set_current_time_zone(Utf16View);
 void clear_system_time_zone_cache();
-Vector<String> const& available_time_zones();
-Vector<String> available_time_zones_in_region(StringView region);
-Optional<String> resolve_primary_time_zone(StringView time_zone);
+Vector<Utf16String> const& available_time_zones();
+Vector<Utf16String> available_time_zones_in_region(Utf16View region);
+Optional<Utf16String> resolve_primary_time_zone(StringView time_zone);
 Optional<TimeZoneOffset> time_zone_offset(StringView time_zone, UnixDateTime time);
 Vector<TimeZoneOffset> disambiguated_time_zone_offsets(StringView time_zone, UnixDateTime time);
 Optional<TimeZoneTransition> get_time_zone_transition(StringView time_zone, UnixDateTime time, TimeZoneTransition::Options options);
diff --git a/Libraries/LibUnicode/UnicodeKeywords.cpp b/Libraries/LibUnicode/UnicodeKeywords.cpp
index 5e69e827f8..e7437a7517 100644
--- a/Libraries/LibUnicode/UnicodeKeywords.cpp
+++ b/Libraries/LibUnicode/UnicodeKeywords.cpp
@@ -19,7 +19,7 @@
 
 namespace Unicode {
 
-Vector<String> available_keyword_values(StringView locale, StringView key)
+Vector<Utf16String> available_keyword_values(Utf16View locale, Utf16View key)
 {
     if (key == "ca"sv)
         return available_calendars(locale);
@@ -36,10 +36,17 @@ Vector<String> available_keyword_values(StringView locale, StringView key)
     TODO();
 }
 
-Vector<String> const& available_calendars()
+static bool is_available_calendar(char const* value, size_t value_length)
 {
-    static NeverDestroyed<Vector<String>> calendars { []() {
-        auto calendars = available_calendars("und"sv);
+    // "islamic" and "islamic-rgsa" are deprecated calendar types that DateTimeFormat resolves to other calendars,
+    // so they should not be advertised as available.
+    return !StringView { value, value_length }.is_one_of("islamic"sv, "islamic-rgsa"sv);
+}
+
+Vector<Utf16String> const& available_calendars()
+{
+    static NeverDestroyed<Vector<Utf16String>> calendars { []() -> Vector<Utf16String> {
+        auto calendars = available_calendars(Utf16View { "und"sv });
 
         quick_sort(calendars);
         return calendars;
@@ -48,11 +55,11 @@ Vector<String> const& available_calendars()
     return *calendars;
 }
 
-Vector<String> available_calendars(StringView locale)
+Vector<Utf16String> available_calendars(Utf16View locale)
 {
     UErrorCode status = U_ZERO_ERROR;
 
-    auto locale_data = LocaleData::for_locale(locale);
+    auto locale_data = LocaleData::for_locale(locale.bytes());
     if (!locale_data.has_value())
         return {};
 
@@ -60,16 +67,27 @@ Vector<String> available_calendars(StringView locale)
     if (icu_failure(status))
         return {};
 
-    return icu_string_enumeration_to_list(move(keywords), "ca", [](char const* value, size_t value_length) {
-        // "islamic" and "islamic-rgsa" are deprecated calendar types that DateTimeFormat resolves to other calendars,
-        // so they should not be advertised as available.
-        return !StringView { value, value_length }.is_one_of("islamic"sv, "islamic-rgsa"sv);
-    });
+    Vector<Utf16String> result;
+    while (true) {
+        i32 length = 0;
+        auto const* value = keywords->next(&length, status);
+
+        if (icu_failure(status) || value == nullptr)
+            break;
+
+        if (!is_available_calendar(value, static_cast<size_t>(length)))
+            continue;
+
+        if (auto const* bcp47_value = uloc_toUnicodeLocaleType("ca", value))
+            result.append(Utf16String::from_ascii_without_validation(StringView { bcp47_value, strlen(bcp47_value) }.bytes()));
+    }
+
+    return result;
 }
 
-Vector<String> const& available_currencies()
+Vector<Utf16String> const& available_currencies()
 {
-    static NeverDestroyed<Vector<String>> currencies { []() -> Vector<String> {
+    static NeverDestroyed<Vector<Utf16String>> currencies { []() -> Vector<Utf16String> {
         UErrorCode status = U_ZERO_ERROR;
 
         auto* currencies = ucurr_openISOCurrencies(UCURR_ALL, &status);
@@ -78,7 +96,7 @@ Vector<String> const& available_currencies()
         if (icu_failure(status))
             return {};
 
-        Vector<String> result;
+        Vector<Utf16String> result;
 
         while (true) {
             i32 length = 0;
@@ -91,7 +109,7 @@ Vector<String> const& available_currencies()
 
             // https://unicode-org.atlassian.net/browse/ICU-21687
             if (StringView currency { next, static_cast<size_t>(length) }; currency != "LSM"sv)
-                result.append(MUST(String::from_utf8(currency)));
+                result.append(Utf16String::from_utf8(currency));
         }
 
         quick_sort(result);
@@ -101,32 +119,54 @@ Vector<String> const& available_currencies()
     return *currencies;
 }
 
-Vector<String> const& available_collation_case_orderings()
+Vector<Utf16String> const& available_collation_case_orderings()
 {
-    static NeverDestroyed<Vector<String>> case_orderings { Vector<String> { "false"_string, "lower"_string, "upper"_string } };
+    static NeverDestroyed<Vector<Utf16String>> case_orderings { [] {
+        return Vector<Utf16String> {
+            Utf16String::from_ascii_without_validation("false"sv.bytes()),
+            Utf16String::from_ascii_without_validation("lower"sv.bytes()),
+            Utf16String::from_ascii_without_validation("upper"sv.bytes()),
+        };
+    }() };
     return *case_orderings;
 }
 
-Vector<String> const& available_collation_numeric_orderings()
+Vector<Utf16String> const& available_collation_numeric_orderings()
 {
-    static NeverDestroyed<Vector<String>> case_orderings { Vector<String> { "false"_string, "true"_string } };
-    return *case_orderings;
+    static NeverDestroyed<Vector<Utf16String>> numeric_orderings { [] {
+        return Vector<Utf16String> {
+            Utf16String::from_ascii_without_validation("false"sv.bytes()),
+            Utf16String::from_ascii_without_validation("true"sv.bytes()),
+        };
+    }() };
+    return *numeric_orderings;
 }
 
-Vector<String> const& available_collations()
+Vector<Utf16String> const& available_collations()
 {
-    static NeverDestroyed<Vector<String>> collations { []() -> Vector<String> {
+    static NeverDestroyed<Vector<Utf16String>> collations { []() -> Vector<Utf16String> {
         UErrorCode status = U_ZERO_ERROR;
 
         auto keywords = adopt_own_if_nonnull(icu::Collator::getKeywordValues("collation", status));
         if (icu_failure(status))
             return {};
 
-        auto collations = icu_string_enumeration_to_list(move(keywords), "co", [](char const* value, size_t value_length) {
+        Vector<Utf16String> collations;
+        while (true) {
+            i32 length = 0;
+            auto const* value = keywords->next(&length, status);
+
+            if (icu_failure(status) || value == nullptr)
+                break;
+
             // https://tc39.es/ecma402/#sec-properties-of-intl-collator-instances
             // the values "standard" and "search" are not allowed
-            return !StringView { value, value_length }.is_one_of("standard"sv, "search"sv);
-        });
+            if (StringView { value, static_cast<size_t>(length) }.is_one_of("standard"sv, "search"sv))
+                continue;
+
+            if (auto const* bcp47_value = uloc_toUnicodeLocaleType("co", value))
+                collations.append(Utf16String::from_ascii_without_validation(StringView { bcp47_value, strlen(bcp47_value) }.bytes()));
+        }
 
         quick_sort(collations);
         return collations;
@@ -135,11 +175,11 @@ Vector<String> const& available_collations()
     return *collations;
 }
 
-Vector<String> available_collations(StringView locale)
+Vector<Utf16String> available_collations(Utf16View locale)
 {
     UErrorCode status = U_ZERO_ERROR;
 
-    auto locale_data = LocaleData::for_locale(locale);
+    auto locale_data = LocaleData::for_locale(locale.bytes());
     if (!locale_data.has_value())
         return {};
 
@@ -147,32 +187,51 @@ Vector<String> available_collations(StringView locale)
     if (icu_failure(status))
         return {};
 
-    auto collations = icu_string_enumeration_to_list(move(keywords), "co", [](char const* value, size_t value_length) {
+    Vector<Utf16String> collations;
+    while (true) {
+        i32 length = 0;
+        auto const* value = keywords->next(&length, status);
+
+        if (icu_failure(status) || value == nullptr)
+            break;
+
         // https://tc39.es/ecma402/#sec-properties-of-intl-collator-instances
         // the values "standard" and "search" are not allowed
-        return !StringView { value, value_length }.is_one_of("standard"sv, "search"sv);
-    });
+        if (StringView { value, static_cast<size_t>(length) }.is_one_of("standard"sv, "search"sv))
+            continue;
 
-    if (!collations.contains_slow("default"sv))
-        collations.prepend("default"_string);
+        if (auto const* bcp47_value = uloc_toUnicodeLocaleType("co", value))
+            collations.append(Utf16String::from_ascii_without_validation(StringView { bcp47_value, strlen(bcp47_value) }.bytes()));
+    }
+
+    auto default_collation = Utf16String::from_ascii_without_validation("default"sv.bytes());
+    if (!collations.contains_slow(default_collation))
+        collations.prepend(default_collation);
 
     return collations;
 }
 
-Vector<String> const& available_hour_cycles()
+Vector<Utf16String> const& available_hour_cycles()
 {
-    static NeverDestroyed<Vector<String>> hour_cycles { Vector<String> { "h11"_string, "h12"_string, "h23"_string, "h24"_string } };
+    static NeverDestroyed<Vector<Utf16String>> hour_cycles { [] {
+        return Vector<Utf16String> {
+            Utf16String::from_ascii_without_validation("h11"sv.bytes()),
+            Utf16String::from_ascii_without_validation("h12"sv.bytes()),
+            Utf16String::from_ascii_without_validation("h23"sv.bytes()),
+            Utf16String::from_ascii_without_validation("h24"sv.bytes()),
+        };
+    }() };
     return *hour_cycles;
 }
 
-Vector<String> available_hour_cycles(StringView locale)
+Vector<Utf16String> available_hour_cycles(Utf16View locale)
 {
     auto preferred_hour_cycle = default_hour_cycle(locale);
     if (!preferred_hour_cycle.has_value())
         return available_hour_cycles();
 
-    Vector<String> hour_cycles;
-    hour_cycles.append(MUST(String::from_utf8(hour_cycle_to_string(*preferred_hour_cycle))));
+    Vector<Utf16String> hour_cycles;
+    hour_cycles.append(available_hour_cycles()[to_underlying(*preferred_hour_cycle)]);
 
     for (auto const& hour_cycle : available_hour_cycles()) {
         if (hour_cycle != hour_cycles[0])
@@ -182,22 +241,32 @@ Vector<String> available_hour_cycles(StringView locale)
     return hour_cycles;
 }
 
-Vector<String> const& available_number_systems()
+Vector<Utf16String> const& available_number_systems()
 {
-    static NeverDestroyed<Vector<String>> number_systems { []() -> Vector<String> {
+    static NeverDestroyed<Vector<Utf16String>> number_systems { []() -> Vector<Utf16String> {
         UErrorCode status = U_ZERO_ERROR;
 
         auto keywords = adopt_own_if_nonnull(icu::NumberingSystem::getAvailableNames(status));
         if (icu_failure(status))
             return {};
 
-        auto number_systems = icu_string_enumeration_to_list(move(keywords), "nu", [&](char const* keyword, size_t) {
+        Vector<Utf16String> number_systems;
+        while (true) {
+            i32 length = 0;
+            auto const* keyword = keywords->next(&length, status);
+
+            if (icu_failure(status) || keyword == nullptr)
+                break;
+
             auto system = adopt_own_if_nonnull(icu::NumberingSystem::createInstanceByName(keyword, status));
             if (icu_failure(status))
-                return false;
+                return {};
 
-            return !static_cast<bool>(system->isAlgorithmic());
-        });
+            if (!static_cast<bool>(system->isAlgorithmic())) {
+                if (auto const* bcp47_value = uloc_toUnicodeLocaleType("nu", keyword))
+                    number_systems.append(Utf16String::from_ascii_without_validation(StringView { bcp47_value, strlen(bcp47_value) }.bytes()));
+            }
+        }
 
         quick_sort(number_systems);
         return number_systems;
@@ -206,16 +275,16 @@ Vector<String> const& available_number_systems()
     return *number_systems;
 }
 
-Vector<String> available_number_systems(StringView locale)
+Vector<Utf16String> available_number_systems(Utf16View locale)
 {
-    auto locale_data = LocaleData::for_locale(locale);
+    auto locale_data = LocaleData::for_locale(locale.bytes());
     if (!locale_data.has_value())
         return {};
 
-    Vector<String> number_systems;
+    Vector<Utf16String> number_systems;
 
     auto const* preferred_number_system = locale_data->numbering_system().getName();
-    number_systems.append(MUST(String::from_utf8({ preferred_number_system, strlen(preferred_number_system) })));
+    number_systems.append(Utf16String::from_ascii_without_validation(StringView { preferred_number_system, strlen(preferred_number_system) }.bytes()));
 
     for (auto const& number_system : available_number_systems()) {
         if (number_system != number_systems[0])
diff --git a/Libraries/LibUnicode/UnicodeKeywords.h b/Libraries/LibUnicode/UnicodeKeywords.h
index e73afd2add..2fca0d6b6a 100644
--- a/Libraries/LibUnicode/UnicodeKeywords.h
+++ b/Libraries/LibUnicode/UnicodeKeywords.h
@@ -8,27 +8,29 @@
 
 #include <AK/String.h>
 #include <AK/StringView.h>
+#include <AK/Utf16String.h>
+#include <AK/Utf16View.h>
 #include <AK/Vector.h>
 
 namespace Unicode {
 
-Vector<String> available_keyword_values(StringView locale, StringView key);
+Vector<Utf16String> available_keyword_values(Utf16View locale, Utf16View key);
 
-Vector<String> const& available_calendars();
-Vector<String> available_calendars(StringView locale);
+Vector<Utf16String> const& available_calendars();
+Vector<Utf16String> available_calendars(Utf16View locale);
 
-Vector<String> const& available_currencies();
+Vector<Utf16String> const& available_currencies();
 
-Vector<String> const& available_collation_case_orderings();
-Vector<String> const& available_collation_numeric_orderings();
+Vector<Utf16String> const& available_collation_case_orderings();
+Vector<Utf16String> const& available_collation_numeric_orderings();
 
-Vector<String> const& available_collations();
-Vector<String> available_collations(StringView locale);
+Vector<Utf16String> const& available_collations();
+Vector<Utf16String> available_collations(Utf16View locale);
 
-Vector<String> const& available_hour_cycles();
-Vector<String> available_hour_cycles(StringView locale);
+Vector<Utf16String> const& available_hour_cycles();
+Vector<Utf16String> available_hour_cycles(Utf16View locale);
 
-Vector<String> const& available_number_systems();
-Vector<String> available_number_systems(StringView locale);
+Vector<Utf16String> const& available_number_systems();
+Vector<Utf16String> available_number_systems(Utf16View locale);
 
 }
diff --git a/Libraries/LibWeb/Animations/KeyframeEffect.cpp b/Libraries/LibWeb/Animations/KeyframeEffect.cpp
index 9244ff8a05..e398c63f25 100644
--- a/Libraries/LibWeb/Animations/KeyframeEffect.cpp
+++ b/Libraries/LibWeb/Animations/KeyframeEffect.cpp
@@ -109,10 +109,10 @@ static WebIDL::ExceptionOr<KeyframeType<AL>> process_a_keyframe_like_object(JS::
     auto& keyframe_object = keyframe_input.as_object();
     auto composite = TRY(keyframe_object.get("composite"_utf16_fly_string));
     if (composite.is_undefined())
-        composite = JS::PrimitiveString::create(vm, "auto"_string);
+        composite = JS::PrimitiveString::create(vm, "auto"_utf16_fly_string);
     auto easing = TRY(keyframe_object.get("easing"_utf16_fly_string));
     if (easing.is_undefined())
-        easing = JS::PrimitiveString::create(vm, "linear"_string);
+        easing = JS::PrimitiveString::create(vm, "linear"_utf16_fly_string);
     auto offset = TRY(keyframe_object.get("offset"_utf16_fly_string));
 
     if constexpr (AL == AllowLists::Yes) {
@@ -865,7 +865,7 @@ WebIDL::ExceptionOr<GC::RootVector<JS::Object*>> KeyframeEffect::get_keyframes()
             TRY(object->set(vm.names.offset, keyframe.offset.has_value() ? JS::Value(keyframe.offset.value()) : JS::js_null(), ShouldThrowExceptions::Yes));
             TRY(object->set(vm.names.computedOffset, JS::Value(keyframe.computed_offset.value()), ShouldThrowExceptions::Yes));
             auto easing_value = keyframe.easing.get<CSS::EasingFunction>();
-            TRY(object->set(vm.names.easing, JS::PrimitiveString::create(vm, easing_value.to_string()), ShouldThrowExceptions::Yes));
+            TRY(object->set(vm.names.easing, JS::PrimitiveString::create(vm, Utf16String::from_utf8(easing_value.to_string())), ShouldThrowExceptions::Yes));
 
             if (keyframe.composite == Bindings::CompositeOperationOrAuto::Replace) {
                 TRY(object->set(vm.names.composite, JS::PrimitiveString::create(vm, "replace"sv), ShouldThrowExceptions::Yes));
@@ -879,7 +879,7 @@ WebIDL::ExceptionOr<GC::RootVector<JS::Object*>> KeyframeEffect::get_keyframes()
 
             for (auto const& [id, value] : keyframe.parsed_properties()) {
                 auto key = Utf16FlyString::from_utf8(CSS::camel_case_string_from_property_id(id));
-                auto value_string = JS::PrimitiveString::create(vm, value->to_string(CSS::SerializationMode::Normal));
+                auto value_string = JS::PrimitiveString::create(vm, Utf16String::from_utf8(value->to_string(CSS::SerializationMode::Normal)));
                 TRY(object->set(JS::PropertyKey { move(key), JS::PropertyKey::StringMayBeNumber::No }, value_string, ShouldThrowExceptions::Yes));
             }
 
diff --git a/Libraries/LibWeb/Bindings/AudioConstructor.cpp b/Libraries/LibWeb/Bindings/AudioConstructor.cpp
index f61d00b54c..46d8693c1f 100644
--- a/Libraries/LibWeb/Bindings/AudioConstructor.cpp
+++ b/Libraries/LibWeb/Bindings/AudioConstructor.cpp
@@ -28,7 +28,7 @@ void AudioConstructor::initialize(JS::Realm& realm)
     Base::initialize(realm);
 
     define_direct_property(vm.names.length, JS::Value(0), JS::Attribute::Configurable);
-    define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, "Audio"_string), JS::Attribute::Configurable);
+    define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, "Audio"_utf16_fly_string), JS::Attribute::Configurable);
     define_direct_property(vm.names.prototype, &ensure_web_prototype<Bindings::HTMLAudioElementPrototype>(realm, "HTMLAudioElement"_fly_string), 0);
 }
 
diff --git a/Libraries/LibWeb/Bindings/ImageConstructor.cpp b/Libraries/LibWeb/Bindings/ImageConstructor.cpp
index 5f5adb25d0..18a052e489 100644
--- a/Libraries/LibWeb/Bindings/ImageConstructor.cpp
+++ b/Libraries/LibWeb/Bindings/ImageConstructor.cpp
@@ -29,7 +29,7 @@ void ImageConstructor::initialize(JS::Realm& realm)
     Base::initialize(realm);
 
     define_direct_property(vm.names.length, JS::Value(0), JS::Attribute::Configurable);
-    define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, "Image"_string), JS::Attribute::Configurable);
+    define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, "Image"_utf16_fly_string), JS::Attribute::Configurable);
     define_direct_property(vm.names.prototype, &ensure_web_prototype<Bindings::HTMLImageElementPrototype>(realm, "HTMLImageElement"_fly_string), 0);
 }
 
diff --git a/Libraries/LibWeb/Bindings/InterfaceObject.cpp b/Libraries/LibWeb/Bindings/InterfaceObject.cpp
index 905bccb840..0ee47d3efd 100644
--- a/Libraries/LibWeb/Bindings/InterfaceObject.cpp
+++ b/Libraries/LibWeb/Bindings/InterfaceObject.cpp
@@ -25,11 +25,6 @@ static Utf16FlyString utf16_fly_string_from_metadata_name(StringView name)
     return Utf16FlyString::from_utf8_without_validation(name);
 }
 
-static String string_from_metadata_name(StringView name)
-{
-    return MUST(String::from_utf8(name));
-}
-
 InterfacePrototypeObject::InterfacePrototypeObject(JS::Realm& realm, InterfaceObjectMetadata const& metadata)
     : Object(realm, metadata.ensure_parent_prototype ? nullptr : realm.intrinsics().object_prototype().ptr())
     , m_metadata(metadata)
@@ -44,10 +39,10 @@ void InterfacePrototypeObject::initialize(JS::Realm& realm)
         m_metadata.initialize_prototype(realm, *this);
     } else if (m_metadata.ensure_parent_prototype) {
         set_prototype(&m_metadata.ensure_parent_prototype(realm));
-        define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, string_from_metadata_name(m_metadata.namespaced_name)), JS::Attribute::Configurable);
+        define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, utf16_fly_string_from_metadata_name(m_metadata.namespaced_name)), JS::Attribute::Configurable);
     } else {
         set_prototype(realm.intrinsics().object_prototype());
-        define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, string_from_metadata_name(m_metadata.namespaced_name)), JS::Attribute::Configurable);
+        define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, utf16_fly_string_from_metadata_name(m_metadata.namespaced_name)), JS::Attribute::Configurable);
     }
 
     Base::initialize(realm);
@@ -98,7 +93,7 @@ void InterfaceConstructor::initialize(JS::Realm& realm)
     if (m_metadata.ensure_parent_constructor)
         set_prototype(&m_metadata.ensure_parent_constructor(realm));
     define_direct_property(vm.names.length, JS::Value(0), JS::Attribute::Configurable);
-    define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, string_from_metadata_name(m_metadata.name)), JS::Attribute::Configurable);
+    define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, utf16_fly_string_from_metadata_name(m_metadata.name)), JS::Attribute::Configurable);
     define_direct_property(vm.names.prototype, &host_defined_intrinsics(realm).existing_web_prototype(fly_string_from_metadata_name(m_metadata.namespaced_name)), 0);
 }
 
diff --git a/Libraries/LibWeb/Bindings/MainThreadVM.cpp b/Libraries/LibWeb/Bindings/MainThreadVM.cpp
index 5ef4a42391..0c72d7c69e 100644
--- a/Libraries/LibWeb/Bindings/MainThreadVM.cpp
+++ b/Libraries/LibWeb/Bindings/MainThreadVM.cpp
@@ -410,7 +410,7 @@ void initialize_main_thread_vm(AgentType type)
             }));
 
             // 3. Return the serialization of url.
-            return JS::PrimitiveString::create(vm, url.serialize());
+            return JS::PrimitiveString::create(vm, Utf16String::from_utf8(url.serialize()));
         };
 
         // 4. Let resolveFunction be ! CreateBuiltinFunction(steps, 1, "resolve", « »).
@@ -418,7 +418,7 @@ void initialize_main_thread_vm(AgentType type)
 
         // 5. Return « Record { [[Key]]: "url", [[Value]]: urlString }, Record { [[Key]]: "resolve", [[Value]]: resolveFunction } ».
         HashMap<JS::PropertyKey, JS::Value> meta;
-        meta.set("url"_utf16_fly_string, JS::PrimitiveString::create(vm, move(url_string)));
+        meta.set("url"_utf16_fly_string, JS::PrimitiveString::create(vm, Utf16String::from_utf8(url_string)));
         meta.set("resolve"_utf16_fly_string, resolve_function);
 
         return meta;
diff --git a/Libraries/LibWeb/Bindings/OptionConstructor.cpp b/Libraries/LibWeb/Bindings/OptionConstructor.cpp
index 93daf6ee20..30cfe0360b 100644
--- a/Libraries/LibWeb/Bindings/OptionConstructor.cpp
+++ b/Libraries/LibWeb/Bindings/OptionConstructor.cpp
@@ -31,7 +31,7 @@ void OptionConstructor::initialize(JS::Realm& realm)
     Base::initialize(realm);
 
     define_direct_property(vm.names.length, JS::Value(0), JS::Attribute::Configurable);
-    define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, "Option"_string), JS::Attribute::Configurable);
+    define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, "Option"_utf16_fly_string), JS::Attribute::Configurable);
     define_direct_property(vm.names.prototype, &ensure_web_prototype<Bindings::HTMLOptionElementPrototype>(realm, "HTMLOptionElement"_fly_string), 0);
 }
 
diff --git a/Libraries/LibWeb/Bindings/PlatformObject.cpp b/Libraries/LibWeb/Bindings/PlatformObject.cpp
index aee23d3fe5..e91dc9d312 100644
--- a/Libraries/LibWeb/Bindings/PlatformObject.cpp
+++ b/Libraries/LibWeb/Bindings/PlatformObject.cpp
@@ -426,7 +426,7 @@ JS::ThrowCompletionOr<GC::RootVector<JS::Value>> PlatformObject::internal_own_pr
     if (m_legacy_platform_object_flags->supports_named_properties) {
         for (auto& named_property : supported_property_names()) {
             if (TRY(is_named_property_exposed_on_object(Utf16FlyString::from_utf8(named_property))))
-                keys.append(JS::PrimitiveString::create(vm, named_property));
+                keys.append(JS::PrimitiveString::create(vm, Utf16FlyString::from_utf8(named_property)));
         }
     }
 
diff --git a/Libraries/LibWeb/CSS/CSSDescriptors.cpp b/Libraries/LibWeb/CSS/CSSDescriptors.cpp
index 4f273ed656..47fcd21777 100644
--- a/Libraries/LibWeb/CSS/CSSDescriptors.cpp
+++ b/Libraries/LibWeb/CSS/CSSDescriptors.cpp
@@ -31,14 +31,14 @@ size_t CSSDescriptors::length() const
 }
 
 // https://drafts.csswg.org/cssom/#dom-cssstyledeclaration-item
-String CSSDescriptors::item(size_t index) const
+Utf16String CSSDescriptors::item(size_t index) const
 {
     // The item(index) method must return the property name of the CSS declaration at position index.
     // If there is no indexth object in the collection, then the method must return the empty string.
     if (index >= length())
         return {};
 
-    return m_descriptors[index].descriptor_name_and_id.name().to_utf16_string().to_utf8_but_should_be_ported_to_utf16();
+    return m_descriptors[index].descriptor_name_and_id.name().to_utf16_string();
 }
 
 // https://drafts.csswg.org/cssom/#set-a-css-declaration
diff --git a/Libraries/LibWeb/CSS/CSSDescriptors.h b/Libraries/LibWeb/CSS/CSSDescriptors.h
index ad59ebed73..ad8ba87169 100644
--- a/Libraries/LibWeb/CSS/CSSDescriptors.h
+++ b/Libraries/LibWeb/CSS/CSSDescriptors.h
@@ -20,7 +20,7 @@ public:
     virtual ~CSSDescriptors() override;
 
     virtual size_t length() const override;
-    virtual String item(size_t index) const override;
+    virtual Utf16String item(size_t index) const override;
     virtual WebIDL::ExceptionOr<void> set_property(Utf16FlyString const& property, StringView value, StringView priority) override;
     virtual WebIDL::ExceptionOr<String> remove_property(Utf16FlyString const& property) override;
     virtual String get_property_value(Utf16FlyString const& property) const override;
diff --git a/Libraries/LibWeb/CSS/CSSFontFeatureValuesMap.cpp b/Libraries/LibWeb/CSS/CSSFontFeatureValuesMap.cpp
index ababf0d8bc..4474a2ff56 100644
--- a/Libraries/LibWeb/CSS/CSSFontFeatureValuesMap.cpp
+++ b/Libraries/LibWeb/CSS/CSSFontFeatureValuesMap.cpp
@@ -56,7 +56,7 @@ WebIDL::ExceptionOr<void> CSSFontFeatureValuesMap::set(String const& feature_val
     for (auto const& value : value_vector)
         wrapped_values.append(JS::Value { value });
 
-    m_map_entries->map_set(JS::PrimitiveString::create(vm(), feature_value_name), JS::Array::create_from(realm(), wrapped_values.span()));
+    m_map_entries->map_set(JS::PrimitiveString::create(vm(), Utf16String::from_utf8(feature_value_name)), JS::Array::create_from(realm(), wrapped_values.span()));
 
     m_parent_rule->clear_caches();
 
diff --git a/Libraries/LibWeb/CSS/CSSStyleDeclaration.h b/Libraries/LibWeb/CSS/CSSStyleDeclaration.h
index 8dffef1587..c3cecbe4f8 100644
--- a/Libraries/LibWeb/CSS/CSSStyleDeclaration.h
+++ b/Libraries/LibWeb/CSS/CSSStyleDeclaration.h
@@ -8,6 +8,7 @@
 #pragma once
 
 #include <AK/String.h>
+#include <AK/Utf16String.h>
 #include <LibWeb/Bindings/PlatformObject.h>
 #include <LibWeb/CSS/CSSRule.h>
 #include <LibWeb/CSS/StyleProperty.h>
@@ -28,7 +29,7 @@ public:
     virtual void initialize(JS::Realm&) override;
 
     virtual size_t length() const = 0;
-    virtual String item(size_t index) const = 0;
+    virtual Utf16String item(size_t index) const = 0;
 
     virtual WebIDL::ExceptionOr<void> set_property(Utf16FlyString const& property_name, StringView css_text, StringView priority) = 0;
     virtual WebIDL::ExceptionOr<String> remove_property(Utf16FlyString const& property_name) = 0;
diff --git a/Libraries/LibWeb/CSS/CSSStyleProperties.cpp b/Libraries/LibWeb/CSS/CSSStyleProperties.cpp
index 7a241d93bb..c52c5034b2 100644
--- a/Libraries/LibWeb/CSS/CSSStyleProperties.cpp
+++ b/Libraries/LibWeb/CSS/CSSStyleProperties.cpp
@@ -143,7 +143,7 @@ size_t CSSStyleProperties::length() const
     return m_properties.size() + m_custom_properties.size();
 }
 
-String CSSStyleProperties::item(size_t index) const
+Utf16String CSSStyleProperties::item(size_t index) const
 {
     // The item(index) method must return the property name of the CSS declaration at position index.
     // If there is no indexth object in the collection, then the method must return the empty string.
@@ -154,13 +154,13 @@ String CSSStyleProperties::item(size_t index) const
 
     if (is_computed()) {
         auto property_id = static_cast<PropertyID>(index + to_underlying(first_longhand_property_id));
-        return string_from_property_id(property_id).to_string();
+        return Utf16String::from_utf8(string_from_property_id(property_id));
     }
 
     if (index < custom_properties_count)
-        return m_custom_properties.keys()[index].to_utf16_string().to_utf8_but_should_be_ported_to_utf16();
+        return m_custom_properties.keys()[index].to_utf16_string();
 
-    return CSS::string_from_property_id(m_properties[index - custom_properties_count].property_id).to_string();
+    return Utf16String::from_utf8(CSS::string_from_property_id(m_properties[index - custom_properties_count].property_id));
 }
 
 Optional<StyleProperty> CSSStyleProperties::get_property(PropertyID property_id) const
diff --git a/Libraries/LibWeb/CSS/CSSStyleProperties.h b/Libraries/LibWeb/CSS/CSSStyleProperties.h
index 025c344dfc..baa95a9eb5 100644
--- a/Libraries/LibWeb/CSS/CSSStyleProperties.h
+++ b/Libraries/LibWeb/CSS/CSSStyleProperties.h
@@ -30,7 +30,7 @@ public:
     virtual void initialize(JS::Realm&) override;
 
     virtual size_t length() const override;
-    virtual String item(size_t index) const override;
+    virtual Utf16String item(size_t index) const override;
 
     Optional<StyleProperty> get_property(PropertyID) const;
     Optional<StyleProperty const&> custom_property(Utf16FlyString const& custom_property_name) const;
diff --git a/Libraries/LibWeb/CSS/CSSUnparsedValue.cpp b/Libraries/LibWeb/CSS/CSSUnparsedValue.cpp
index 1a5ae4ff15..a4de9eff5c 100644
--- a/Libraries/LibWeb/CSS/CSSUnparsedValue.cpp
+++ b/Libraries/LibWeb/CSS/CSSUnparsedValue.cpp
@@ -24,7 +24,7 @@ GC::Ref<CSSUnparsedValue> CSSUnparsedValue::create(JS::Realm& realm, ReadonlySpa
     for (auto const& variant : value) {
         variant.visit(
             [&](GC::Ref<CSSVariableReferenceValue> it) { converted_value.append(it); },
-            [&](String const& it) { converted_value.append(it); });
+            [&](Utf16String const& it) { converted_value.append(it); });
     }
 
     return realm.create<CSSUnparsedValue>(realm, move(converted_value));
@@ -83,14 +83,14 @@ Optional<JS::Value> CSSUnparsedValue::item_value(size_t index) const
     auto value = m_tokens[index];
     return value.visit(
         [&](GC::Ref<CSSVariableReferenceValue> const& variable) -> JS::Value { return variable; },
-        [&](String const& string) -> JS::Value { return JS::PrimitiveString::create(vm(), string); });
+        [&](Utf16String const& string) -> JS::Value { return JS::PrimitiveString::create(vm(), string); });
 }
 
 static WebIDL::ExceptionOr<CSSUnparsedSegment> unparsed_segment_from_js_value(JS::VM& vm, JS::Value& value)
 {
     if (auto variable_reference = value.as_if<CSSVariableReferenceValue>())
         return GC::Ref { *variable_reference };
-    return TRY(value.to_utf16_string(vm)).to_utf8_but_should_be_ported_to_utf16();
+    return TRY(value.to_utf16_string(vm));
 }
 
 // https://drafts.css-houdini.org/css-typed-om-1/#ref-for-dfn-set-the-value-of-an-existing-indexed-property
@@ -150,8 +150,8 @@ WebIDL::ExceptionOr<Utf16String> CSSUnparsedValue::to_string() const
         //        serialize_a_series_of_component_values(). See https://github.com/w3c/css-houdini-drafts/issues/1148
         TRY(item.visit(
             // 1. If item is a USVString, append it to s.
-            [&](String const& string) -> WebIDL::ExceptionOr<void> {
-                s.append(Utf16String::from_utf8_without_validation(string));
+            [&](Utf16String const& string) -> WebIDL::ExceptionOr<void> {
+                s.append(string);
                 return {};
             },
             // 2. Otherwise, item is a CSSVariableReferenceValue. Serialize it, then append the result to s.
diff --git a/Libraries/LibWeb/CSS/CSSUnparsedValue.h b/Libraries/LibWeb/CSS/CSSUnparsedValue.h
index e72560d7d7..66674b38d7 100644
--- a/Libraries/LibWeb/CSS/CSSUnparsedValue.h
+++ b/Libraries/LibWeb/CSS/CSSUnparsedValue.h
@@ -11,7 +11,7 @@
 
 namespace Web::CSS {
 
-using CSSUnparsedSegment = Variant<String, GC::Ref<CSSVariableReferenceValue>>;
+using CSSUnparsedSegment = Variant<Utf16String, GC::Ref<CSSVariableReferenceValue>>;
 
 // https://drafts.css-houdini.org/css-typed-om-1/#cssunparsedvalue
 class CSSUnparsedValue final : public CSSStyleValue {
diff --git a/Libraries/LibWeb/CSS/CSSUnparsedValue.idl b/Libraries/LibWeb/CSS/CSSUnparsedValue.idl
index 8500b5f19a..68ded73935 100644
--- a/Libraries/LibWeb/CSS/CSSUnparsedValue.idl
+++ b/Libraries/LibWeb/CSS/CSSUnparsedValue.idl
@@ -9,4 +9,4 @@ interface CSSUnparsedValue : CSSStyleValue {
 };
 
 // https://drafts.css-houdini.org/css-typed-om-1/#typedefdef-cssunparsedsegment
-typedef (USVString or CSSVariableReferenceValue) CSSUnparsedSegment;
+typedef (Utf16USVString or CSSVariableReferenceValue) CSSUnparsedSegment;
diff --git a/Libraries/LibWeb/CSS/MediaList.cpp b/Libraries/LibWeb/CSS/MediaList.cpp
index 2ccbab41a0..de3595800e 100644
--- a/Libraries/LibWeb/CSS/MediaList.cpp
+++ b/Libraries/LibWeb/CSS/MediaList.cpp
@@ -156,7 +156,7 @@ Optional<JS::Value> MediaList::item_value(size_t index) const
 {
     if (index >= m_media.size())
         return {};
-    return JS::PrimitiveString::create(vm(), m_media[index]->to_string());
+    return JS::PrimitiveString::create(vm(), Utf16String::from_utf8(m_media[index]->to_string()));
 }
 
 void MediaList::dump(StringBuilder& builder, int indent_levels) const
diff --git a/Libraries/LibWeb/CSS/StyleValues/UnresolvedStyleValue.cpp b/Libraries/LibWeb/CSS/StyleValues/UnresolvedStyleValue.cpp
index fb8d227a4d..65bcb68647 100644
--- a/Libraries/LibWeb/CSS/StyleValues/UnresolvedStyleValue.cpp
+++ b/Libraries/LibWeb/CSS/StyleValues/UnresolvedStyleValue.cpp
@@ -197,7 +197,7 @@ private:
 
     void serialize_unserialized_values()
     {
-        m_reified_values.append(serialize_a_series_of_component_values(m_unserialized_values));
+        m_reified_values.append(Utf16String::from_utf8(serialize_a_series_of_component_values(m_unserialized_values)));
         m_unserialized_values.clear_with_capacity();
     }
 
diff --git a/Libraries/LibWeb/Clipboard/Clipboard.cpp b/Libraries/LibWeb/Clipboard/Clipboard.cpp
index 34c18ebfd2..b321f8abfd 100644
--- a/Libraries/LibWeb/Clipboard/Clipboard.cpp
+++ b/Libraries/LibWeb/Clipboard/Clipboard.cpp
@@ -89,7 +89,7 @@ static String os_specific_well_known_format(StringView mime_type_string)
 }
 
 // https://w3c.github.io/clipboard-apis/#write-blobs-and-option-to-the-clipboard
-static void write_blobs_and_option_to_clipboard(JS::Realm& realm, ReadonlySpan<GC::Ref<FileAPI::Blob>> items, StringView presentation_style)
+static void write_blobs_and_option_to_clipboard(JS::Realm& realm, ReadonlySpan<GC::Ref<FileAPI::Blob>> items, Utf16String const& presentation_style)
 {
     auto& window = as<HTML::Window>(realm.global_object());
 
@@ -118,7 +118,7 @@ static void write_blobs_and_option_to_clipboard(JS::Realm& realm, ReadonlySpan<G
         auto payload = MUST(TextCodec::convert_input_to_utf8_using_given_decoder_unless_there_is_a_byte_order_mark(*decoder, item->raw_bytes()));
 
         // 4. Insert payload and presentationStyle into the system clipboard using formatString as the native clipboard format.
-        window.page().client().page_did_insert_clipboard_entry({ payload.to_byte_string(), move(format_string) }, presentation_style);
+        window.page().client().page_did_insert_clipboard_entry({ payload.to_byte_string(), move(format_string) }, presentation_style.to_byte_string());
     }
 
     // FIXME: 3. Write web custom formats given webCustomFormats.
@@ -234,7 +234,7 @@ GC::Ref<WebIDL::Promise> Clipboard::read(Bindings::ClipboardUnsanitizedFormats f
                         .mime_type = move(mime_type),
 
                         // 7. Resolve representation’s data with systemClipboardRepresentation’s data.
-                        .data = WebIDL::create_resolved_promise(realm, JS::PrimitiveString::create(realm.vm(), move(string))),
+                        .data = WebIDL::create_resolved_promise(realm, JS::PrimitiveString::create(realm.vm(), Utf16String::from_utf8(string))),
                     };
 
                     // 5. Let isUnsanitized be false.
@@ -381,7 +381,7 @@ GC::Ref<WebIDL::Promise> Clipboard::read_text()
                             auto decoder = TextCodec::decoder_for("UTF-8"sv);
                             auto string = MUST(TextCodec::convert_input_to_utf8_using_given_decoder_unless_there_is_a_byte_order_mark(*decoder, system_clipboard_representation.data));
 
-                            WebIDL::resolve_promise(realm, promise, JS::PrimitiveString::create(realm.vm(), move(string)));
+                            WebIDL::resolve_promise(realm, promise, JS::PrimitiveString::create(realm.vm(), Utf16String::from_utf8(string)));
                             return;
                         }
                     }
@@ -578,7 +578,7 @@ GC::Ref<WebIDL::Promise> Clipboard::write_text(String data)
             item_list.append(text_blob);
 
             // 4. Let option be set to "unspecified".
-            static constexpr auto option = "unspecified"sv;
+            auto option = "unspecified"_utf16;
 
             // 5. Write blobs and option to the clipboard with itemList and option.
             write_blobs_and_option_to_clipboard(realm, item_list, option);
diff --git a/Libraries/LibWeb/Crypto/CryptoAlgorithms.cpp b/Libraries/LibWeb/Crypto/CryptoAlgorithms.cpp
index 69fade855a..8b4e0f8ad0 100644
--- a/Libraries/LibWeb/Crypto/CryptoAlgorithms.cpp
+++ b/Libraries/LibWeb/Crypto/CryptoAlgorithms.cpp
@@ -98,7 +98,13 @@ static ::Crypto::UnsignedBigInteger big_integer_from_api_big_integer(GC::Ptr<JS:
 }
 
 // https://www.rfc-editor.org/rfc/rfc7518#section-2
-ErrorOr<String> base64_url_uint_encode(::Crypto::UnsignedBigInteger integer)
+static ErrorOr<Utf16String> base64_url_bytes_encode(ReadonlyBytes bytes)
+{
+    auto encoded = TRY(encode_base64url(bytes, AK::OmitPadding::Yes));
+    return Utf16String::from_ascii_without_validation(encoded.bytes_as_string_view().bytes());
+}
+
+ErrorOr<Utf16String> base64_url_uint_encode(::Crypto::UnsignedBigInteger integer)
 {
     // The representation of a positive or zero integer value as the
     // base64url encoding of the value's unsigned big-endian
@@ -109,14 +115,17 @@ ErrorOr<String> base64_url_uint_encode(::Crypto::UnsignedBigInteger integer)
 
     auto bytes = TRY(ByteBuffer::create_uninitialized(integer.byte_length()));
     auto result = integer.export_data(bytes.span());
-    return TRY(encode_base64url(result, AK::OmitPadding::Yes));
+    return TRY(base64_url_bytes_encode(result));
 }
 
-WebIDL::ExceptionOr<ByteBuffer> base64_url_bytes_decode(JS::Realm& realm, String const& base64_url_string)
+WebIDL::ExceptionOr<ByteBuffer> base64_url_bytes_decode(JS::Realm& realm, Utf16String const& base64_url_string)
 {
     auto& vm = realm.vm();
 
-    auto base64_bytes_or_error = decode_base64url(base64_url_string, AK::LastChunkHandling::Loose);
+    if (!base64_url_string.is_ascii())
+        return WebIDL::DataError::create(realm, "base64 decode: invalid base64url"_utf16);
+
+    auto base64_bytes_or_error = decode_base64url(base64_url_string.to_byte_string(), AK::LastChunkHandling::Loose);
     if (base64_bytes_or_error.is_error()) {
         if (base64_bytes_or_error.error().code() == ENOMEM)
             return vm.throw_completion<JS::InternalError>(vm.error_message(::JS::VM::ErrorMessage::OutOfMemory));
@@ -125,7 +134,7 @@ WebIDL::ExceptionOr<ByteBuffer> base64_url_bytes_decode(JS::Realm& realm, String
     return base64_bytes_or_error.release_value();
 }
 
-WebIDL::ExceptionOr<::Crypto::UnsignedBigInteger> base64_url_uint_decode(JS::Realm& realm, String const& base64_url_string)
+WebIDL::ExceptionOr<::Crypto::UnsignedBigInteger> base64_url_uint_decode(JS::Realm& realm, Utf16String const& base64_url_string)
 {
     auto base64_bytes_be = TRY(base64_url_bytes_decode(realm, base64_url_string));
     return ::Crypto::UnsignedBigInteger::import_data(base64_bytes_be);
@@ -231,7 +240,7 @@ static WebIDL::ExceptionOr<void> validate_jwk_key_ops(JS::Realm& realm, JsonWebK
     auto key_operations = *jwk.key_ops;
 
     // Duplicate key operation values MUST NOT be present in the array
-    HashTable<String> seen_operations;
+    HashTable<Utf16String> seen_operations;
     for (auto const& key_operation : key_operations) {
         if (seen_operations.set(key_operation) != HashSetResult::InsertedNewEntry)
             return WebIDL::DataError::create(realm, Utf16String::formatted("Duplicate key operation: {}", key_operation));
@@ -241,9 +250,9 @@ static WebIDL::ExceptionOr<void> validate_jwk_key_ops(JS::Realm& realm, JsonWebK
     // vulnerabilities associated with using the same key with multiple algorithms.  Thus, the
     // combinations "sign" with "verify", "encrypt" with "decrypt", and "wrapKey" with "unwrapKey"
     // are permitted, but other combinations SHOULD NOT be used.
-    auto is_used_for_signing = seen_operations.contains("sign"sv) || seen_operations.contains("verify"sv);
-    auto is_used_for_encryption = seen_operations.contains("encrypt"sv) || seen_operations.contains("decrypt"sv);
-    auto is_used_for_wrapping = seen_operations.contains("wrapKey"sv) || seen_operations.contains("unwrapKey"sv);
+    auto is_used_for_signing = seen_operations.contains("sign"_utf16) || seen_operations.contains("verify"_utf16);
+    auto is_used_for_encryption = seen_operations.contains("encrypt"_utf16) || seen_operations.contains("decrypt"_utf16);
+    auto is_used_for_wrapping = seen_operations.contains("wrapKey"_utf16) || seen_operations.contains("unwrapKey"_utf16);
     auto number_of_operation_types = is_used_for_signing + is_used_for_encryption + is_used_for_wrapping;
     if (number_of_operation_types > 1)
         return WebIDL::DataError::create(realm, "Multiple unrelated key operations are specified"_utf16);
@@ -253,11 +262,11 @@ static WebIDL::ExceptionOr<void> validate_jwk_key_ops(JS::Realm& realm, JsonWebK
     // members they use, if either is to be used by the application.
     if (jwk.use.has_value()) {
         for (auto const& key_operation : key_operations) {
-            if (key_operation == "deriveKey"sv || key_operation == "deriveBits"sv)
+            if (key_operation == "deriveKey"_utf16 || key_operation == "deriveBits"_utf16)
                 continue;
-            if (jwk.use == "sig"sv && key_operation != "sign"sv && key_operation != "verify"sv)
+            if (jwk.use == "sig"_utf16 && key_operation != "sign"_utf16 && key_operation != "verify"_utf16)
                 return WebIDL::DataError::create(realm, "use=sig but key_ops does not contain 'sign' or 'verify'"_utf16);
-            if (jwk.use == "enc"sv && (key_operation == "sign"sv || key_operation == "verify"sv))
+            if (jwk.use == "enc"_utf16 && (key_operation == "sign"_utf16 || key_operation == "verify"_utf16))
                 return WebIDL::DataError::create(realm, "use=enc but key_ops contains 'sign' or 'verify'"_utf16);
         }
     }
@@ -520,7 +529,7 @@ JS::ThrowCompletionOr<NonnullOwnPtr<AlgorithmParams>> EcKeyGenParams::from_value
     auto& object = value.as_object();
 
     auto curve_value = TRY(object.get("namedCurve"_utf16_fly_string));
-    auto curve = TRY(curve_value.to_utf16_string(vm)).to_utf8_but_should_be_ported_to_utf16();
+    auto curve = TRY(curve_value.to_utf16_string(vm));
 
     return adopt_own<AlgorithmParams>(*new EcKeyGenParams { curve });
 }
@@ -574,7 +583,7 @@ JS::ThrowCompletionOr<NonnullOwnPtr<AlgorithmParams>> EcKeyImportParams::from_va
     auto& object = value.as_object();
 
     auto named_curve_value = TRY(object.get("namedCurve"_utf16_fly_string));
-    auto named_curve = TRY(named_curve_value.to_utf16_string(vm)).to_utf8_but_should_be_ported_to_utf16();
+    auto named_curve = TRY(named_curve_value.to_utf16_string(vm));
 
     return adopt_own<AlgorithmParams>(*new EcKeyImportParams { named_curve });
 }
@@ -1051,11 +1060,11 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> RSAOAEP::import_key(Web::Crypto::Algorit
         }
 
         // 4. If the kty field of jwk is not a case-sensitive string match to "RSA", then throw a DataError.
-        if (jwk.kty != "RSA"_string)
+        if (jwk.kty != "RSA"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 5. If usages is non-empty and the use field of jwk is present and is not a case-sensitive string match to "enc", then throw a DataError.
-        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"_string)
+        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid use field"_utf16);
 
         // 6. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web Key [JWK]
@@ -1072,22 +1081,22 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> RSAOAEP::import_key(Web::Crypto::Algorit
             //     Let hash be undefined.
         }
         //    ->  If the alg field of jwk is equal to "RSA-OAEP":
-        else if (jwk.alg == "RSA-OAEP"sv) {
+        else if (*jwk.alg == "RSA-OAEP"_utf16) {
             //     Let hash be the string "SHA-1".
             hash = "SHA-1"_string;
         }
         //    -> If the alg field of jwk is equal to "RSA-OAEP-256":
-        else if (jwk.alg == "RSA-OAEP-256"sv) {
+        else if (*jwk.alg == "RSA-OAEP-256"_utf16) {
             //     Let hash be the string "SHA-256".
             hash = "SHA-256"_string;
         }
         //    -> If the alg field of jwk is equal to "RSA-OAEP-384":
-        else if (jwk.alg == "RSA-OAEP-384"sv) {
+        else if (*jwk.alg == "RSA-OAEP-384"_utf16) {
             //     Let hash be the string "SHA-384".
             hash = "SHA-384"_string;
         }
         //    -> If the alg field of jwk is equal to "RSA-OAEP-512":
-        else if (jwk.alg == "RSA-OAEP-512"sv) {
+        else if (*jwk.alg == "RSA-OAEP-512"_utf16) {
             //     Let hash be the string "SHA-512".
             hash = "SHA-512"_string;
         }
@@ -1271,7 +1280,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> RSAOAEP::export_key(Bindings::KeyFormat
         JsonWebKey jwk = {};
 
         // 2. Set the kty attribute of jwk to the string "RSA".
-        jwk.kty = "RSA"_string;
+        jwk.kty = "RSA"_utf16;
 
         // 4. Let hash be the name attribute of the hash attribute of the [[algorithm]] internal slot of key.
         auto hash = TRY(as<RsaHashedKeyAlgorithm>(*key->algorithm()).hash().name(vm));
@@ -1279,22 +1288,22 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> RSAOAEP::export_key(Bindings::KeyFormat
         // 4. If hash is "SHA-1":
         //      - Set the alg attribute of jwk to the string "RSA-OAEP".
         if (hash == "SHA-1"sv) {
-            jwk.alg = "RSA-OAEP"_string;
+            jwk.alg = "RSA-OAEP"_utf16;
         }
         //    If hash is "SHA-256":
         //      - Set the alg attribute of jwk to the string "RSA-OAEP-256".
         else if (hash == "SHA-256"sv) {
-            jwk.alg = "RSA-OAEP-256"_string;
+            jwk.alg = "RSA-OAEP-256"_utf16;
         }
         //    If hash is "SHA-384":
         //      - Set the alg attribute of jwk to the string "RSA-OAEP-384".
         else if (hash == "SHA-384"sv) {
-            jwk.alg = "RSA-OAEP-384"_string;
+            jwk.alg = "RSA-OAEP-384"_utf16;
         }
         //    If hash is "SHA-512":
         //      - Set the alg attribute of jwk to the string "RSA-OAEP-512".
         else if (hash == "SHA-512"sv) {
-            jwk.alg = "RSA-OAEP-512"_string;
+            jwk.alg = "RSA-OAEP-512"_utf16;
         } else {
             // - Perform any key export steps defined by other applicable specifications,
             //   passing format and the hash attribute of the [[algorithm]] internal slot of key and obtaining alg.
@@ -1333,7 +1342,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> RSAOAEP::export_key(Bindings::KeyFormat
         TRY_OR_THROW_OOM(vm, maybe_error);
 
         // 13. Set the key_ops attribute of jwk to the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages()) {
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
@@ -1633,11 +1642,11 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> RSAPSS::import_key(AlgorithmParams const
         }
 
         // 3. If the kty field of jwk is not a case-sensitive string match to "RSA", then throw a DataError.
-        if (jwk.kty != "RSA"_string)
+        if (jwk.kty != "RSA"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 4. If usages is non-empty and the use field of jwk is present and is not a case-sensitive string match to "sig", then throw a DataError.
-        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "sig"_string)
+        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "sig"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid use field"_utf16);
 
         // 5. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web Key [JWK]
@@ -1654,22 +1663,22 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> RSAPSS::import_key(AlgorithmParams const
             //     Let hash be undefined.
         }
         //    ->  If the alg field of jwk is equal to "PS1":
-        else if (jwk.alg == "PS1"sv) {
+        else if (*jwk.alg == "PS1"_utf16) {
             //     Let hash be the string "SHA-1".
             hash = "SHA-1"_string;
         }
         //    -> If the alg field of jwk is equal to "PS256":
-        else if (jwk.alg == "PS256"sv) {
+        else if (*jwk.alg == "PS256"_utf16) {
             //     Let hash be the string "SHA-256".
             hash = "SHA-256"_string;
         }
         //    -> If the alg field of jwk is equal to "PS384":
-        else if (jwk.alg == "PS384"sv) {
+        else if (*jwk.alg == "PS384"_utf16) {
             //     Let hash be the string "SHA-384".
             hash = "SHA-384"_string;
         }
         //    -> If the alg field of jwk is equal to "PS512":
-        else if (jwk.alg == "PS512"sv) {
+        else if (*jwk.alg == "PS512"_utf16) {
             //     Let hash be the string "SHA-512".
             hash = "SHA-512"_string;
         }
@@ -1853,7 +1862,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> RSAPSS::export_key(Bindings::KeyFormat
         JsonWebKey jwk = {};
 
         // 2. Set the kty attribute of jwk to the string "RSA".
-        jwk.kty = "RSA"_string;
+        jwk.kty = "RSA"_utf16;
 
         // 3. Let hash be the name attribute of the hash attribute of the [[algorithm]] internal slot of key.
         auto hash = TRY(as<RsaHashedKeyAlgorithm>(*key->algorithm()).hash().name(vm));
@@ -1861,22 +1870,22 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> RSAPSS::export_key(Bindings::KeyFormat
         // 4. If hash is "SHA-1":
         //      - Set the alg attribute of jwk to the string "PS1".
         if (hash == "SHA-1"sv) {
-            jwk.alg = "PS1"_string;
+            jwk.alg = "PS1"_utf16;
         }
         //    If hash is "SHA-256":
         //      - Set the alg attribute of jwk to the string "PS256".
         else if (hash == "SHA-256"sv) {
-            jwk.alg = "PS256"_string;
+            jwk.alg = "PS256"_utf16;
         }
         //    If hash is "SHA-384":
         //      - Set the alg attribute of jwk to the string "PS384".
         else if (hash == "SHA-384"sv) {
-            jwk.alg = "PS384"_string;
+            jwk.alg = "PS384"_utf16;
         }
         //    If hash is "SHA-512":
         //      - Set the alg attribute of jwk to the string "PS512".
         else if (hash == "SHA-512"sv) {
-            jwk.alg = "PS512"_string;
+            jwk.alg = "PS512"_utf16;
         } else {
             // - Perform any key export steps defined by other applicable specifications,
             //   passing format and the hash attribute of the [[algorithm]] internal slot of key and obtaining alg.
@@ -1916,7 +1925,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> RSAPSS::export_key(Bindings::KeyFormat
         TRY_OR_THROW_OOM(vm, maybe_error);
 
         // 7. Set the key_ops attribute of jwk to the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages()) {
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
@@ -2210,11 +2219,11 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> RSASSAPKCS1::import_key(AlgorithmParams
         }
 
         // 3. If the kty field of jwk is not a case-sensitive string match to "RSA", then throw a DataError.
-        if (jwk.kty != "RSA"_string)
+        if (jwk.kty != "RSA"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 4. If usages is non-empty and the use field of jwk is present and is not a case-sensitive string match to "sig", then throw a DataError.
-        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "sig"_string)
+        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "sig"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid use field"_utf16);
 
         // 5. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web Key [JWK]
@@ -2231,22 +2240,22 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> RSASSAPKCS1::import_key(AlgorithmParams
             //     Let hash be undefined.
         }
         //    ->  If the alg field of jwk is equal to "RS1":
-        else if (jwk.alg == "RS1"sv) {
+        else if (*jwk.alg == "RS1"_utf16) {
             //     Let hash be the string "SHA-1".
             hash = "SHA-1"_string;
         }
         //    -> If the alg field of jwk is equal to "RS256":
-        else if (jwk.alg == "RS256"sv) {
+        else if (*jwk.alg == "RS256"_utf16) {
             //     Let hash be the string "SHA-256".
             hash = "SHA-256"_string;
         }
         //    -> If the alg field of jwk is equal to "RS384":
-        else if (jwk.alg == "RS384"sv) {
+        else if (*jwk.alg == "RS384"_utf16) {
             //     Let hash be the string "SHA-384".
             hash = "SHA-384"_string;
         }
         //    -> If the alg field of jwk is equal to "RS512":
-        else if (jwk.alg == "RS512"sv) {
+        else if (*jwk.alg == "RS512"_utf16) {
             //     Let hash be the string "SHA-512".
             hash = "SHA-512"_string;
         }
@@ -2430,7 +2439,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> RSASSAPKCS1::export_key(Bindings::KeyFo
         JsonWebKey jwk = {};
 
         // 2. Set the kty attribute of jwk to the string "RSA".
-        jwk.kty = "RSA"_string;
+        jwk.kty = "RSA"_utf16;
 
         // 3. Let hash be the name attribute of the hash attribute of the [[algorithm]] internal slot of key.
         auto hash = TRY(as<RsaHashedKeyAlgorithm>(*key->algorithm()).hash().name(vm));
@@ -2438,22 +2447,22 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> RSASSAPKCS1::export_key(Bindings::KeyFo
         // 4. If hash is "SHA-1":
         //      - Set the alg attribute of jwk to the string "RS1".
         if (hash == "SHA-1"sv) {
-            jwk.alg = "RS1"_string;
+            jwk.alg = "RS1"_utf16;
         }
         //    If hash is "SHA-256":
         //      - Set the alg attribute of jwk to the string "RS256".
         else if (hash == "SHA-256"sv) {
-            jwk.alg = "RS256"_string;
+            jwk.alg = "RS256"_utf16;
         }
         //    If hash is "SHA-384":
         //      - Set the alg attribute of jwk to the string "RS384".
         else if (hash == "SHA-384"sv) {
-            jwk.alg = "RS384"_string;
+            jwk.alg = "RS384"_utf16;
         }
         //    If hash is "SHA-512":
         //      - Set the alg attribute of jwk to the string "RS512".
         else if (hash == "SHA-512"sv) {
-            jwk.alg = "RS512"_string;
+            jwk.alg = "RS512"_utf16;
         } else {
             // - Perform any key export steps defined by other applicable specifications,
             //   passing format and the hash attribute of the [[algorithm]] internal slot of key and obtaining alg.
@@ -2493,7 +2502,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> RSASSAPKCS1::export_key(Bindings::KeyFo
         TRY_OR_THROW_OOM(vm, maybe_error);
 
         // 7. Set the key_ops attribute of jwk to the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages()) {
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
@@ -2596,7 +2605,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> AesCbc::import_key(AlgorithmParams const
         auto& jwk = key_data.get<JsonWebKey>();
 
         //    2. If the kty field of jwk is not "oct", then throw a DataError.
-        if (jwk.kty != "oct"_string)
+        if (jwk.kty != "oct"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         //    3. If jwk does not meet the requirements of Section 6.4 of JSON Web Algorithms [JWA], then throw a DataError.
@@ -2618,15 +2627,15 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> AesCbc::import_key(AlgorithmParams const
         auto data_bits = data.size() * 8;
         auto const& alg = jwk.alg;
         if (data_bits == 128) {
-            if (alg.has_value() && alg != "A128CBC") {
+            if (alg.has_value() && *alg != "A128CBC"_utf16) {
                 return WebIDL::DataError::create(m_realm, "Contradictory key size: key has 128 bits, but alg specifies non-128-bit algorithm"_utf16);
             }
         } else if (data_bits == 192) {
-            if (alg.has_value() && alg != "A192CBC") {
+            if (alg.has_value() && *alg != "A192CBC"_utf16) {
                 return WebIDL::DataError::create(m_realm, "Contradictory key size: key has 192 bits, but alg specifies non-192-bit algorithm"_utf16);
             }
         } else if (data_bits == 256) {
-            if (alg.has_value() && alg != "A256CBC") {
+            if (alg.has_value() && *alg != "A256CBC"_utf16) {
                 return WebIDL::DataError::create(m_realm, "Contradictory key size: key has 256 bits, but alg specifies non-256-bit algorithm"_utf16);
             }
         } else {
@@ -2634,7 +2643,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> AesCbc::import_key(AlgorithmParams const
         }
 
         //    6. If usages is non-empty and the use field of jwk is present and is not "enc", then throw a DataError.
-        if (!key_usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"_string)
+        if (!key_usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid use field"_utf16);
 
         //    7. If the key_ops field of jwk is present, and is invalid according to the
@@ -2751,11 +2760,11 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> AesCbc::export_key(Bindings::KeyFormat
         JsonWebKey jwk = {};
 
         // 2. Set the kty attribute of jwk to the string "oct".
-        jwk.kty = "oct"_string;
+        jwk.kty = "oct"_utf16;
 
         // 3. Set the k attribute of jwk to be a string containing the raw octets of the key represented by [[handle]] internal slot of key, encoded according to Section 6.4 of JSON Web Algorithms [JWA].
         auto const& key_bytes = handle.get<ByteBuffer>();
-        jwk.k = TRY_OR_THROW_OOM(m_realm->vm(), encode_base64url(key_bytes, AK::OmitPadding::Yes));
+        jwk.k = TRY_OR_THROW_OOM(m_realm->vm(), base64_url_bytes_encode(key_bytes));
 
         // 4. -> If the length attribute of key is 128:
         //        Set the alg attribute of jwk to the string "A128CBC".
@@ -2765,17 +2774,17 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> AesCbc::export_key(Bindings::KeyFormat
         //        Set the alg attribute of jwk to the string "A256CBC".
         auto key_bits = key_bytes.size() * 8;
         if (key_bits == 128) {
-            jwk.alg = "A128CBC"_string;
+            jwk.alg = "A128CBC"_utf16;
         } else if (key_bits == 192) {
-            jwk.alg = "A192CBC"_string;
+            jwk.alg = "A192CBC"_utf16;
         } else if (key_bits == 256) {
-            jwk.alg = "A256CBC"_string;
+            jwk.alg = "A256CBC"_utf16;
         } else {
             return WebIDL::OperationError::create(m_realm, "unclear key size"_utf16);
         }
 
         // 5. Set the key_ops attribute of jwk to equal the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages()) {
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
@@ -2847,7 +2856,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> AesCtr::import_key(AlgorithmParams const
         auto& jwk = key_data.get<JsonWebKey>();
 
         // 2. If the kty field of jwk is not "oct", then throw a DataError.
-        if (jwk.kty != "oct"_string)
+        if (jwk.kty != "oct"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 3. If jwk does not meet the requirements of Section 6.4 of JSON Web Algorithms [JWA], then throw a DataError.
@@ -2875,20 +2884,20 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> AesCtr::import_key(AlgorithmParams const
         auto data_bits = data.size() * 8;
         auto const& alg = jwk.alg;
         if (data_bits == 128) {
-            if (alg.has_value() && alg != "A128CTR")
+            if (alg.has_value() && *alg != "A128CTR"_utf16)
                 return WebIDL::DataError::create(m_realm, "Contradictory key size: key has 128 bits, but alg specifies non-128-bit algorithm"_utf16);
         } else if (data_bits == 192) {
-            if (alg.has_value() && alg != "A192CTR")
+            if (alg.has_value() && *alg != "A192CTR"_utf16)
                 return WebIDL::DataError::create(m_realm, "Contradictory key size: key has 192 bits, but alg specifies non-192-bit algorithm"_utf16);
         } else if (data_bits == 256) {
-            if (alg.has_value() && alg != "A256CTR")
+            if (alg.has_value() && *alg != "A256CTR"_utf16)
                 return WebIDL::DataError::create(m_realm, "Contradictory key size: key has 256 bits, but alg specifies non-256-bit algorithm"_utf16);
         } else {
             return WebIDL::DataError::create(m_realm, Utf16String::formatted("Invalid key size: {} bits", data_bits));
         }
 
         // 6. If usages is non-empty and the use field of jwk is present and is not "enc", then throw a DataError.
-        if (!key_usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"_string)
+        if (!key_usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid use field"_utf16);
 
         // 7. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web Key [JWK]
@@ -2955,12 +2964,12 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> AesCtr::export_key(Bindings::KeyFormat
         JsonWebKey jwk = {};
 
         // 2. Set the kty attribute of jwk to the string "oct".
-        jwk.kty = "oct"_string;
+        jwk.kty = "oct"_utf16;
 
         // 3. Set the k attribute of jwk to be a string containing the raw octets of the key represented by [[handle]] internal slot of key,
         //    encoded according to Section 6.4 of JSON Web Algorithms [JWA].
         auto const& key_bytes = key->handle().get<ByteBuffer>();
-        jwk.k = TRY_OR_THROW_OOM(m_realm->vm(), encode_base64url(key_bytes, AK::OmitPadding::Yes));
+        jwk.k = TRY_OR_THROW_OOM(m_realm->vm(), base64_url_bytes_encode(key_bytes));
 
         // 4. -> If the length attribute of key is 128:
         //        Set the alg attribute of jwk to the string "A128CTR".
@@ -2970,15 +2979,15 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> AesCtr::export_key(Bindings::KeyFormat
         //        Set the alg attribute of jwk to the string "A256CTR".
         auto key_bits = key_bytes.size() * 8;
         if (key_bits == 128) {
-            jwk.alg = "A128CTR"_string;
+            jwk.alg = "A128CTR"_utf16;
         } else if (key_bits == 192) {
-            jwk.alg = "A192CTR"_string;
+            jwk.alg = "A192CTR"_utf16;
         } else if (key_bits == 256) {
-            jwk.alg = "A256CTR"_string;
+            jwk.alg = "A256CTR"_utf16;
         }
 
         // 5. Set the key_ops attribute of jwk to the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages()) {
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
@@ -3169,7 +3178,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> AesGcm::import_key(AlgorithmParams const
         auto& jwk = key_data.get<JsonWebKey>();
 
         // 2. If the kty field of jwk is not "oct", then throw a DataError.
-        if (jwk.kty != "oct"_string)
+        if (jwk.kty != "oct"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 3. If jwk does not meet the requirements of Section 6.4 of JSON Web Algorithms [JWA], then throw a DataError.
@@ -3197,20 +3206,20 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> AesGcm::import_key(AlgorithmParams const
         auto data_bits = data.size() * 8;
         auto const& alg = jwk.alg;
         if (data_bits == 128) {
-            if (alg.has_value() && alg != "A128GCM")
+            if (alg.has_value() && *alg != "A128GCM"_utf16)
                 return WebIDL::DataError::create(m_realm, "Contradictory key size: key has 128 bits, but alg specifies non-128-bit algorithm"_utf16);
         } else if (data_bits == 192) {
-            if (alg.has_value() && alg != "A192GCM")
+            if (alg.has_value() && *alg != "A192GCM"_utf16)
                 return WebIDL::DataError::create(m_realm, "Contradictory key size: key has 192 bits, but alg specifies non-192-bit algorithm"_utf16);
         } else if (data_bits == 256) {
-            if (alg.has_value() && alg != "A256GCM")
+            if (alg.has_value() && *alg != "A256GCM"_utf16)
                 return WebIDL::DataError::create(m_realm, "Contradictory key size: key has 256 bits, but alg specifies non-256-bit algorithm"_utf16);
         } else {
             return WebIDL::DataError::create(m_realm, Utf16String::formatted("Invalid key size: {} bits", data_bits));
         }
 
         // 6. If usages is non-empty and the use field of jwk is present and is not "enc", then throw a DataError.
-        if (!key_usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"_string)
+        if (!key_usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid use field"_utf16);
 
         // 7. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web Key [JWK]
@@ -3277,12 +3286,12 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> AesGcm::export_key(Bindings::KeyFormat
         JsonWebKey jwk = {};
 
         // 2. Set the kty attribute of jwk to the string "oct".
-        jwk.kty = "oct"_string;
+        jwk.kty = "oct"_utf16;
 
         // 3. Set the k attribute of jwk to be a string containing the raw octets of the key represented by [[handle]] internal slot of key,
         //    encoded according to Section 6.4 of JSON Web Algorithms [JWA].
         auto const& key_bytes = key->handle().get<ByteBuffer>();
-        jwk.k = TRY_OR_THROW_OOM(m_realm->vm(), encode_base64url(key_bytes, AK::OmitPadding::Yes));
+        jwk.k = TRY_OR_THROW_OOM(m_realm->vm(), base64_url_bytes_encode(key_bytes));
 
         // 4. -> If the length attribute of key is 128:
         //        Set the alg attribute of jwk to the string "A128GCM".
@@ -3292,15 +3301,15 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> AesGcm::export_key(Bindings::KeyFormat
         //        Set the alg attribute of jwk to the string "A256GCM".
         auto key_bits = key_bytes.size() * 8;
         if (key_bits == 128) {
-            jwk.alg = "A128GCM"_string;
+            jwk.alg = "A128GCM"_utf16;
         } else if (key_bits == 192) {
-            jwk.alg = "A192GCM"_string;
+            jwk.alg = "A192GCM"_utf16;
         } else if (key_bits == 256) {
-            jwk.alg = "A256GCM"_string;
+            jwk.alg = "A256GCM"_utf16;
         }
 
         // 5. Set the key_ops attribute of jwk to the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages()) {
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
@@ -3521,7 +3530,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> AesKw::import_key(AlgorithmParams const&
         auto& jwk = key_data.get<JsonWebKey>();
 
         // 2. If the kty field of jwk is not "oct", then throw a DataError.
-        if (jwk.kty != "oct"_string)
+        if (jwk.kty != "oct"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 3. If jwk does not meet the requirements of Section 6.4 of JSON Web Algorithms [JWA], then throw a DataError.
@@ -3547,20 +3556,20 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> AesKw::import_key(AlgorithmParams const&
         auto data_bits = data.size() * 8;
         auto const& alg = jwk.alg;
         if (data_bits == 128) {
-            if (alg.has_value() && alg != "A128KW")
+            if (alg.has_value() && *alg != "A128KW"_utf16)
                 return WebIDL::DataError::create(m_realm, "Contradictory key size: key has 128 bits, but alg specifies non-128-bit algorithm"_utf16);
         } else if (data_bits == 192) {
-            if (alg.has_value() && alg != "A192KW")
+            if (alg.has_value() && *alg != "A192KW"_utf16)
                 return WebIDL::DataError::create(m_realm, "Contradictory key size: key has 192 bits, but alg specifies non-192-bit algorithm"_utf16);
         } else if (data_bits == 256) {
-            if (alg.has_value() && alg != "A256KW")
+            if (alg.has_value() && *alg != "A256KW"_utf16)
                 return WebIDL::DataError::create(m_realm, "Contradictory key size: key has 256 bits, but alg specifies non-256-bit algorithm"_utf16);
         } else {
             return WebIDL::DataError::create(m_realm, Utf16String::formatted("Invalid key size: {} bits", data_bits));
         }
 
         // 6. If usages is non-empty and the use field of jwk is present and is not "enc", then throw a DataError.
-        if (!key_usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"_string)
+        if (!key_usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid use field"_utf16);
 
         // 7. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web Key [JWK]
@@ -3627,12 +3636,12 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> AesKw::export_key(Bindings::KeyFormat f
         JsonWebKey jwk = {};
 
         // 2. Set the kty attribute of jwk to the string "oct".
-        jwk.kty = "oct"_string;
+        jwk.kty = "oct"_utf16;
 
         // 3. Set the k attribute of jwk to be a string containing the raw octets of the key represented by [[handle]] internal slot of key,
         //    encoded according to Section 6.4 of JSON Web Algorithms [JWA].
         auto const& key_bytes = key->handle().get<ByteBuffer>();
-        jwk.k = TRY_OR_THROW_OOM(m_realm->vm(), encode_base64url(key_bytes, AK::OmitPadding::Yes));
+        jwk.k = TRY_OR_THROW_OOM(m_realm->vm(), base64_url_bytes_encode(key_bytes));
 
         // 4. -> If the length attribute of key is 128:
         //        Set the alg attribute of jwk to the string "A128KW".
@@ -3642,15 +3651,15 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> AesKw::export_key(Bindings::KeyFormat f
         //        Set the alg attribute of jwk to the string "A256KW".
         auto key_bits = key_bytes.size() * 8;
         if (key_bits == 128) {
-            jwk.alg = "A128KW"_string;
+            jwk.alg = "A128KW"_utf16;
         } else if (key_bits == 192) {
-            jwk.alg = "A192KW"_string;
+            jwk.alg = "A192KW"_utf16;
         } else if (key_bits == 256) {
-            jwk.alg = "A256KW"_string;
+            jwk.alg = "A256KW"_utf16;
         }
 
         // 5. Set the key_ops attribute of jwk to the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages()) {
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
@@ -3868,12 +3877,12 @@ WebIDL::ExceptionOr<Variant<GC::Ref<CryptoKey>, GC::Ref<CryptoKeyPair>>> ECDSA::
     // Generate an Elliptic Curve key pair, as defined in [RFC6090]
     // with domain parameters for the curve identified by the namedCurve member of normalizedAlgorithm.
     Variant<Empty, ::Crypto::Curves::SECP256r1, ::Crypto::Curves::SECP384r1, ::Crypto::Curves::SECP521r1> curve;
-    if (normalized_algorithm.named_curve.is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
-        if (normalized_algorithm.named_curve == "P-256")
+    if (normalized_algorithm.named_curve.is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
+        if (normalized_algorithm.named_curve == "P-256"_utf16)
             curve = ::Crypto::Curves::SECP256r1 {};
-        else if (normalized_algorithm.named_curve == "P-384")
+        else if (normalized_algorithm.named_curve == "P-384"_utf16)
             curve = ::Crypto::Curves::SECP384r1 {};
-        else if (normalized_algorithm.named_curve == "P-521")
+        else if (normalized_algorithm.named_curve == "P-521"_utf16)
             curve = ::Crypto::Curves::SECP521r1 {};
         else
             VERIFY_NOT_REACHED();
@@ -3998,16 +4007,16 @@ WebIDL::ExceptionOr<GC::Ref<JS::ArrayBuffer>> ECDSA::sign(AlgorithmParams const&
     ByteBuffer result;
 
     // 6. If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-256", "P-384" or "P-521":
-    if (named_curve.is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
+    if (named_curve.is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
         size_t coord_size;
         Variant<Empty, ::Crypto::Curves::SECP256r1, ::Crypto::Curves::SECP384r1, ::Crypto::Curves::SECP521r1> curve;
-        if (named_curve == "P-256") {
+        if (named_curve == "P-256"_utf16) {
             coord_size = 256 / 8;
             curve = ::Crypto::Curves::SECP256r1 {};
-        } else if (named_curve == "P-384") {
+        } else if (named_curve == "P-384"_utf16) {
             coord_size = 384 / 8;
             curve = ::Crypto::Curves::SECP384r1 {};
-        } else if (named_curve == "P-521") {
+        } else if (named_curve == "P-521"_utf16) {
             coord_size = ceil_div(521, 8);
             curve = ::Crypto::Curves::SECP521r1 {};
         } else {
@@ -4094,12 +4103,12 @@ WebIDL::ExceptionOr<JS::Value> ECDSA::verify(AlgorithmParams const& params, GC::
     auto result = false;
 
     Variant<Empty, ::Crypto::Curves::SECP256r1, ::Crypto::Curves::SECP384r1, ::Crypto::Curves::SECP521r1> curve;
-    if (named_curve.is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
-        if (named_curve == "P-256")
+    if (named_curve.is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
+        if (named_curve == "P-256"_utf16)
             curve = ::Crypto::Curves::SECP256r1 {};
-        else if (named_curve == "P-384")
+        else if (named_curve == "P-384"_utf16)
             curve = ::Crypto::Curves::SECP384r1 {};
-        else if (named_curve == "P-521")
+        else if (named_curve == "P-521"_utf16)
             curve = ::Crypto::Curves::SECP521r1 {};
         else
             VERIFY_NOT_REACHED();
@@ -4168,22 +4177,22 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDSA::import_key(AlgorithmParams const&
 
         // 7. If params is not an instance of the ECParameters ASN.1 type defined in [RFC5480] that specifies a namedCurve, then throw a DataError.
         // 8. Let namedCurve be a string whose initial value is undefined.
-        String named_curve;
+        NamedCurve named_curve;
 
         // 9. If params is equivalent to the secp256r1 object identifier defined in [RFC5480]:
         if (ec_params == ::Crypto::ASN1::secp256r1_oid) {
             // Set namedCurve to "P-256".
-            named_curve = "P-256"_string;
+            named_curve = "P-256"_utf16;
         }
         // If params is equivalent to the secp384r1 object identifier defined in [RFC5480]:
         else if (ec_params == ::Crypto::ASN1::secp384r1_oid) {
             // Set namedCurve to "P-384".
-            named_curve = "P-384"_string;
+            named_curve = "P-384"_utf16;
         }
         // If params is equivalent to the secp521r1 object identifier defined in [RFC5480]:
         else if (ec_params == ::Crypto::ASN1::secp521r1_oid) {
             // Set namedCurve to "P-521".
-            named_curve = "P-521"_string;
+            named_curve = "P-521"_utf16;
         }
 
         // 10. If namedCurve is not undefined
@@ -4212,11 +4221,11 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDSA::import_key(AlgorithmParams const&
         // 12. If the public key value is not a valid point on the Elliptic Curve identified
         //     by the namedCurve member of normalizedAlgorithm throw a DataError.
         auto curve = [&named_curve] -> Variant<::Crypto::Curves::SECP256r1, ::Crypto::Curves::SECP384r1, ::Crypto::Curves::SECP521r1> {
-            if (named_curve == "P-256")
+            if (named_curve == "P-256"_utf16)
                 return ::Crypto::Curves::SECP256r1 {};
-            if (named_curve == "P-384")
+            if (named_curve == "P-384"_utf16)
                 return ::Crypto::Curves::SECP384r1 {};
-            if (named_curve == "P-521")
+            if (named_curve == "P-521"_utf16)
                 return ::Crypto::Curves::SECP521r1 {};
             VERIFY_NOT_REACHED();
         }();
@@ -4277,22 +4286,22 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDSA::import_key(AlgorithmParams const&
 
         // 7. If params is not an instance of the ECParameters ASN.1 type defined in [RFC5480] that specifies a namedCurve, then throw a DataError.
         // 8. Let namedCurve be a string whose initial value is undefined.
-        String named_curve;
+        NamedCurve named_curve;
 
         // 9. If params is equivalent to the secp256r1 object identifier defined in [RFC5480]:
         if (ec_params == ::Crypto::ASN1::secp256r1_oid) {
             // Set namedCurve to "P-256".
-            named_curve = "P-256"_string;
+            named_curve = "P-256"_utf16;
         }
         // If params is equivalent to the secp384r1 object identifier defined in [RFC5480]:
         else if (ec_params == ::Crypto::ASN1::secp384r1_oid) {
             // Set namedCurve to "P-384".
-            named_curve = "P-384"_string;
+            named_curve = "P-384"_utf16;
         }
         // If params is equivalent to the secp521r1 object identifier defined in [RFC5480]:
         else if (ec_params == ::Crypto::ASN1::secp521r1_oid) {
             // Set namedCurve to "P-521".
-            named_curve = "P-521"_string;
+            named_curve = "P-521"_utf16;
         }
 
         // 10. If namedCurve is not undefined
@@ -4328,11 +4337,11 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDSA::import_key(AlgorithmParams const&
         // 12. If the key value is not a valid point on the Elliptic Curve identified
         //     by the namedCurve member of normalizedAlgorithm throw a DataError.
         auto curve = [&named_curve] -> Variant<::Crypto::Curves::SECP256r1, ::Crypto::Curves::SECP384r1, ::Crypto::Curves::SECP521r1> {
-            if (named_curve == "P-256")
+            if (named_curve == "P-256"_utf16)
                 return ::Crypto::Curves::SECP256r1 {};
-            if (named_curve == "P-384")
+            if (named_curve == "P-384"_utf16)
                 return ::Crypto::Curves::SECP384r1 {};
-            if (named_curve == "P-521")
+            if (named_curve == "P-521"_utf16)
                 return ::Crypto::Curves::SECP521r1 {};
             VERIFY_NOT_REACHED();
         }();
@@ -4393,11 +4402,11 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDSA::import_key(AlgorithmParams const&
         }
 
         // 3. If the kty field of jwk is not "EC", then throw a DataError.
-        if (jwk.kty != "EC"sv)
+        if (jwk.kty != "EC"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 4. If usages is non-empty and the use field of jwk is present and is not "sig", then throw a DataError.
-        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "sig"sv)
+        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "sig"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key use"_utf16);
 
         // 5. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web Key [JWK],
@@ -4419,25 +4428,25 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDSA::import_key(AlgorithmParams const&
             return WebIDL::DataError::create(m_realm, "Invalid algorithm"_utf16);
 
         // 9. If namedCurve is "P-256", "P-384" or "P-521":
-        if (named_curve.is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
+        if (named_curve.is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
             // 1. Let algNamedCurve be a string whose initial value is undefined.
-            String alg_named_curve;
+            NamedCurve alg_named_curve;
 
             // 2. If the alg field is not present:
             //    Let algNamedCurve be undefined.
             if (jwk.alg.has_value()) {
                 // If the alg field is equal to the string "ES256":
-                if (*jwk.alg == "ES256")
+                if (*jwk.alg == "ES256"_utf16)
                     // Let algNamedCurve be the string "P-256".
-                    alg_named_curve = "P-256"_string;
+                    alg_named_curve = "P-256"_utf16;
                 // If the alg field is equal to the string "ES384":
-                else if (*jwk.alg == "ES384")
+                else if (*jwk.alg == "ES384"_utf16)
                     // Let algNamedCurve be the string "P-384".
-                    alg_named_curve = "P-384"_string;
+                    alg_named_curve = "P-384"_utf16;
                 // If the alg field is equal to the string "ES512":
-                else if (*jwk.alg == "ES512")
+                else if (*jwk.alg == "ES512"_utf16)
                     // Let algNamedCurve be the string "P-521".
-                    alg_named_curve = "P-521"_string;
+                    alg_named_curve = "P-521"_utf16;
                 // otherwise:
                 else
                     // throw a DataError.
@@ -4449,11 +4458,11 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDSA::import_key(AlgorithmParams const&
                 return WebIDL::DataError::create(m_realm, "Invalid algorithm"_utf16);
 
             size_t coord_size;
-            if (named_curve == "P-256"sv)
+            if (named_curve == "P-256"_utf16)
                 coord_size = 256 / 8;
-            else if (named_curve == "P-384"sv)
+            else if (named_curve == "P-384"_utf16)
                 coord_size = 384 / 8;
-            else if (named_curve == "P-521"sv)
+            else if (named_curve == "P-521"_utf16)
                 coord_size = ceil_div(521, 8);
             else
                 VERIFY_NOT_REACHED();
@@ -4462,7 +4471,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDSA::import_key(AlgorithmParams const&
             if (!jwk.x.has_value() || !jwk.y.has_value())
                 return WebIDL::DataError::create(m_realm, "Invalid key"_utf16);
 
-            auto maybe_x_bytes = decode_base64url(jwk.x.value());
+            auto maybe_x_bytes = base64_url_bytes_decode(m_realm, jwk.x.value());
             if (maybe_x_bytes.is_error()) {
                 return WebIDL::DataError::create(m_realm, "Failed to decode base64"_utf16);
             }
@@ -4470,7 +4479,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDSA::import_key(AlgorithmParams const&
             if (x_bytes.size() != coord_size)
                 return WebIDL::DataError::create(m_realm, "Invalid key size"_utf16);
 
-            auto maybe_y_bytes = decode_base64url(jwk.y.value());
+            auto maybe_y_bytes = base64_url_bytes_decode(m_realm, jwk.y.value());
             if (maybe_y_bytes.is_error()) {
                 return WebIDL::DataError::create(m_realm, "Failed to decode base64"_utf16);
             }
@@ -4487,7 +4496,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDSA::import_key(AlgorithmParams const&
             // If the d field is present:
             if (jwk.d.has_value()) {
                 // 1. If jwk does not meet the requirements of Section 6.2.2 of JSON Web Algorithms [JWA], then throw a DataError.
-                auto maybe_d_bytes = decode_base64url(jwk.d.value());
+                auto maybe_d_bytes = base64_url_bytes_decode(m_realm, jwk.d.value());
                 if (maybe_d_bytes.is_error()) {
                     return WebIDL::DataError::create(m_realm, "Failed to decode base64"_utf16);
                 }
@@ -4526,11 +4535,11 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDSA::import_key(AlgorithmParams const&
         // 10. If the key value is not a valid point on the Elliptic Curve identified
         //     by the namedCurve member of normalizedAlgorithm throw a DataError.
         auto curve = [&named_curve] -> Variant<::Crypto::Curves::SECP256r1, ::Crypto::Curves::SECP384r1, ::Crypto::Curves::SECP521r1> {
-            if (named_curve == "P-256")
+            if (named_curve == "P-256"_utf16)
                 return ::Crypto::Curves::SECP256r1 {};
-            if (named_curve == "P-384")
+            if (named_curve == "P-384"_utf16)
                 return ::Crypto::Curves::SECP384r1 {};
-            if (named_curve == "P-521")
+            if (named_curve == "P-521"_utf16)
                 return ::Crypto::Curves::SECP521r1 {};
             VERIFY_NOT_REACHED();
         }();
@@ -4568,7 +4577,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDSA::import_key(AlgorithmParams const&
     // For all existing asymmetric algorithms in WebCrypto, "raw-public" acts as an alias of "raw".
     else if (key_format == Bindings::KeyFormat::Raw || key_format == Bindings::KeyFormat::RawPublic) {
         // 1. If the namedCurve member of normalizedAlgorithm is not a named curve, then throw a DataError.
-        if (!normalized_algorithm.named_curve.is_one_of("P-256"sv, "P-384"sv, "P-521"sv))
+        if (!normalized_algorithm.named_curve.is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16))
             return WebIDL::DataError::create(m_realm, "Invalid algorithm"_utf16);
 
         // 2. If usages contains a value which is not "verify" then throw a SyntaxError.
@@ -4579,7 +4588,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDSA::import_key(AlgorithmParams const&
         }
 
         // 3. If namedCurve is "P-256", "P-384" or "P-521":
-        if (normalized_algorithm.named_curve.is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
+        if (normalized_algorithm.named_curve.is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
             auto key_bytes = move(key_data.get<ByteBuffer>());
 
             // 1. Let Q be the Elliptic Curve public key on the curve identified by the namedCurve
@@ -4652,7 +4661,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDSA::export_key(Bindings::KeyFormat f
         //    Set the subjectPublicKey field to keyData
         //    If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-256", "P-384" or "P-521":
         auto& algorithm = static_cast<EcKeyAlgorithm const&>(*key->algorithm());
-        if (algorithm.named_curve().is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
+        if (algorithm.named_curve().is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
             //  Let keyData be the octet string that represents the Elliptic Curve public key represented by the [[handle]] internal slot
             //  of key according to the encoding rules specified in Section 2.3.3 of [SEC1] and using the uncompressed form.
             //  If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-256":
@@ -4667,11 +4676,11 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDSA::export_key(Bindings::KeyFormat f
                     auto public_key_bytes = TRY(public_key.to_uncompressed());
 
                     Span<int const> ec_params;
-                    if (algorithm.named_curve() == "P-256"sv)
+                    if (algorithm.named_curve() == "P-256"_utf16)
                         ec_params = ::Crypto::ASN1::secp256r1_oid;
-                    else if (algorithm.named_curve() == "P-384"sv)
+                    else if (algorithm.named_curve() == "P-384"_utf16)
                         ec_params = ::Crypto::ASN1::secp384r1_oid;
-                    else if (algorithm.named_curve() == "P-521"sv)
+                    else if (algorithm.named_curve() == "P-521"_utf16)
                         ec_params = ::Crypto::ASN1::secp521r1_oid;
                     else
                         VERIFY_NOT_REACHED();
@@ -4715,7 +4724,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDSA::export_key(Bindings::KeyFormat f
         //      Set the parameters field to an instance of the ECParameters ASN.1 type defined in [RFC5480] as follows:
         //          If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-256", "P-384" or "P-521":
         auto& algorithm = static_cast<EcKeyAlgorithm const&>(*key->algorithm());
-        if (algorithm.named_curve().is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
+        if (algorithm.named_curve().is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
             // Let keyData be the result of DER-encoding an instance of the ECPrivateKey structure defined
             // in Section 3 of [RFC5915] for the Elliptic Curve private key represented by the [[handle]] internal slot
             // of key and that conforms to the following:
@@ -4733,11 +4742,11 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDSA::export_key(Bindings::KeyFormat f
             auto maybe_data = handle.visit(
                 [&](::Crypto::PK::ECPrivateKey const& private_key) -> ErrorOr<ByteBuffer> {
                     Span<int const> ec_params;
-                    if (algorithm.named_curve() == "P-256"sv)
+                    if (algorithm.named_curve() == "P-256"_utf16)
                         ec_params = ::Crypto::ASN1::secp256r1_oid;
-                    else if (algorithm.named_curve() == "P-384"sv)
+                    else if (algorithm.named_curve() == "P-384"_utf16)
                         ec_params = ::Crypto::ASN1::secp384r1_oid;
-                    else if (algorithm.named_curve() == "P-521"sv)
+                    else if (algorithm.named_curve() == "P-521"_utf16)
                         ec_params = ::Crypto::ASN1::secp521r1_oid;
                     else
                         VERIFY_NOT_REACHED();
@@ -4770,46 +4779,46 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDSA::export_key(Bindings::KeyFormat f
         JsonWebKey jwk = {};
 
         // 2. Set the kty attribute of jwk to "EC".
-        jwk.kty = "EC"_string;
+        jwk.kty = "EC"_utf16;
 
         // 3. If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-256", "P-384" or "P-521":
         auto& algorithm = static_cast<EcKeyAlgorithm const&>(*key->algorithm());
-        if (algorithm.named_curve().is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
+        if (algorithm.named_curve().is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
             // 1. If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-256":
-            if (algorithm.named_curve() == "P-256"sv) {
+            if (algorithm.named_curve() == "P-256"_utf16) {
                 // Set the crv attribute of jwk to "P-256"
-                jwk.crv = "P-256"_string;
+                jwk.crv = "P-256"_utf16;
             }
             // If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-384":
-            else if (algorithm.named_curve() == "P-384"sv) {
+            else if (algorithm.named_curve() == "P-384"_utf16) {
                 // Set the crv attribute of jwk to "P-384"
-                jwk.crv = "P-384"_string;
+                jwk.crv = "P-384"_utf16;
             }
             // If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-521":
-            else if (algorithm.named_curve() == "P-521"sv) {
+            else if (algorithm.named_curve() == "P-521"_utf16) {
                 // Set the crv attribute of jwk to "P-521"
-                jwk.crv = "P-521"_string;
+                jwk.crv = "P-521"_utf16;
             }
 
             auto maybe_error = handle.visit(
                 [&](::Crypto::PK::ECPublicKey const& public_key) -> ErrorOr<void> {
                     // 2. Set the x attribute of jwk according to the definition in Section 6.2.1.2 of JSON Web Algorithms [JWA].
                     auto x_bytes = TRY(public_key.x_bytes());
-                    jwk.x = TRY(encode_base64url(x_bytes, AK::OmitPadding::Yes));
+                    jwk.x = TRY(base64_url_bytes_encode(x_bytes));
 
                     // 3. Set the y attribute of jwk according to the definition in Section 6.2.1.3 of JSON Web Algorithms [JWA].
                     auto y_bytes = TRY(public_key.y_bytes());
-                    jwk.y = TRY(encode_base64url(y_bytes, AK::OmitPadding::Yes));
+                    jwk.y = TRY(base64_url_bytes_encode(y_bytes));
 
                     return {};
                 },
                 [&](::Crypto::PK::ECPrivateKey const& private_key) -> ErrorOr<void> {
                     Variant<Empty, ::Crypto::Curves::SECP256r1, ::Crypto::Curves::SECP384r1, ::Crypto::Curves::SECP521r1> curve;
-                    if (algorithm.named_curve() == "P-256"sv)
+                    if (algorithm.named_curve() == "P-256"_utf16)
                         curve = ::Crypto::Curves::SECP256r1 {};
-                    else if (algorithm.named_curve() == "P-384"sv)
+                    else if (algorithm.named_curve() == "P-384"_utf16)
                         curve = ::Crypto::Curves::SECP384r1 {};
-                    else if (algorithm.named_curve() == "P-521"sv)
+                    else if (algorithm.named_curve() == "P-521"_utf16)
                         curve = ::Crypto::Curves::SECP521r1 {};
                     else
                         VERIFY_NOT_REACHED();
@@ -4823,10 +4832,10 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDSA::export_key(Bindings::KeyFormat f
                     auto y_bytes = TRY(public_key.y_bytes());
 
                     // 2. Set the x attribute of jwk according to the definition in Section 6.2.1.2 of JSON Web Algorithms [JWA].
-                    jwk.x = TRY(encode_base64url(x_bytes, AK::OmitPadding::Yes));
+                    jwk.x = TRY(base64_url_bytes_encode(x_bytes));
 
                     // 3. Set the y attribute of jwk according to the definition in Section 6.2.1.3 of JSON Web Algorithms [JWA].
-                    jwk.y = TRY(encode_base64url(y_bytes, AK::OmitPadding::Yes));
+                    jwk.y = TRY(base64_url_bytes_encode(y_bytes));
 
                     return {};
                 },
@@ -4843,7 +4852,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDSA::export_key(Bindings::KeyFormat f
                     [&](::Crypto::PK::ECPrivateKey const& private_key) -> ErrorOr<void> {
                         // Set the d attribute of jwk according to the definition in Section 6.2.2.1 of JSON Web Algorithms [JWA].
                         auto d_bytes = TRY(private_key.d_bytes());
-                        jwk.d = TRY(encode_base64url(d_bytes, AK::OmitPadding::Yes));
+                        jwk.d = TRY(base64_url_bytes_encode(d_bytes));
 
                         return {};
                     },
@@ -4863,7 +4872,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDSA::export_key(Bindings::KeyFormat f
         }
 
         // 4. Set the key_ops attribute of jwk to the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages())
             jwk.key_ops->unchecked_append(idl_enum_to_string(usage));
@@ -4887,7 +4896,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDSA::export_key(Bindings::KeyFormat f
 
         // 2. If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-256", "P-384" or "P-521":
         auto& algorithm = static_cast<EcKeyAlgorithm const&>(*key->algorithm());
-        if (algorithm.named_curve().is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
+        if (algorithm.named_curve().is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
             // Let data be an octet string representing the Elliptic Curve point Q represented by [[handle]] internal slot
             // of key according to [SEC1] 2.3.3 using the uncompressed format.
             auto maybe_data = handle.visit(
@@ -4938,12 +4947,12 @@ WebIDL::ExceptionOr<Variant<GC::Ref<CryptoKey>, GC::Ref<CryptoKeyPair>>> ECDH::g
     // Generate an Elliptic Curve key pair, as defined in [RFC6090]
     // with domain parameters for the curve identified by the namedCurve member of normalizedAlgorithm.
     Variant<Empty, ::Crypto::Curves::SECP256r1, ::Crypto::Curves::SECP384r1, ::Crypto::Curves::SECP521r1> curve;
-    if (normalized_algorithm.named_curve.is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
-        if (normalized_algorithm.named_curve == "P-256")
+    if (normalized_algorithm.named_curve.is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
+        if (normalized_algorithm.named_curve == "P-256"_utf16)
             curve = ::Crypto::Curves::SECP256r1 {};
-        else if (normalized_algorithm.named_curve == "P-384")
+        else if (normalized_algorithm.named_curve == "P-384"_utf16)
             curve = ::Crypto::Curves::SECP384r1 {};
-        else if (normalized_algorithm.named_curve == "P-521")
+        else if (normalized_algorithm.named_curve == "P-521"_utf16)
             curve = ::Crypto::Curves::SECP521r1 {};
         else
             VERIFY_NOT_REACHED();
@@ -5058,7 +5067,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::ArrayBuffer>> ECDH::derive_bits(AlgorithmParams
 
     // 6. If the namedCurve property of the [[algorithm]] internal slot of key is "P-256", "P-384" or "P-521":
     // 7. If performing the operation results in an error, then throw a OperationError.
-    if (internal_algorithm.named_curve().is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
+    if (internal_algorithm.named_curve().is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
         // 1. Perform the ECDH primitive specified in [RFC6090] Section 4
         //    with key as the EC private key d and the EC public key represented
         //    by the [[handle]] internal slot of publicKey as the EC public key.
@@ -5068,11 +5077,11 @@ WebIDL::ExceptionOr<GC::Ref<JS::ArrayBuffer>> ECDH::derive_bits(AlgorithmParams
         auto public_key_data = public_key->handle().get<::Crypto::PK::ECPublicKey>();
 
         Variant<Empty, ::Crypto::Curves::SECP256r1, ::Crypto::Curves::SECP384r1, ::Crypto::Curves::SECP521r1> curve;
-        if (internal_algorithm.named_curve() == "P-256"sv)
+        if (internal_algorithm.named_curve() == "P-256"_utf16)
             curve = ::Crypto::Curves::SECP256r1 {};
-        else if (internal_algorithm.named_curve() == "P-384"sv)
+        else if (internal_algorithm.named_curve() == "P-384"_utf16)
             curve = ::Crypto::Curves::SECP384r1 {};
-        else if (internal_algorithm.named_curve() == "P-521"sv)
+        else if (internal_algorithm.named_curve() == "P-521"_utf16)
             curve = ::Crypto::Curves::SECP521r1 {};
         else
             VERIFY_NOT_REACHED();
@@ -5158,22 +5167,22 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDH::import_key(AlgorithmParams const&
 
         // 7. If params is not an instance of the ECParameters ASN.1 type defined in [RFC5480] that specifies a namedCurve, then throw a DataError.
         // 8. Let namedCurve be a string whose initial value is undefined.
-        String named_curve;
+        NamedCurve named_curve;
 
         // 9. If params is equivalent to the secp256r1 object identifier defined in [RFC5480]:
         if (ec_params == ::Crypto::ASN1::secp256r1_oid) {
             // Set namedCurve to "P-256".
-            named_curve = "P-256"_string;
+            named_curve = "P-256"_utf16;
         }
         // If params is equivalent to the secp384r1 object identifier defined in [RFC5480]:
         else if (ec_params == ::Crypto::ASN1::secp384r1_oid) {
             // Set namedCurve to "P-384".
-            named_curve = "P-384"_string;
+            named_curve = "P-384"_utf16;
         }
         // If params is equivalent to the secp521r1 object identifier defined in [RFC5480]:
         else if (ec_params == ::Crypto::ASN1::secp521r1_oid) {
             // Set namedCurve to "P-521".
-            named_curve = "P-521"_string;
+            named_curve = "P-521"_utf16;
         }
 
         // 10. If namedCurve is not undefined
@@ -5202,11 +5211,11 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDH::import_key(AlgorithmParams const&
         // 12. If the key value is not a valid point on the Elliptic Curve identified
         //     by the namedCurve member of normalizedAlgorithm throw a DataError.
         auto curve = [&named_curve] -> Variant<::Crypto::Curves::SECP256r1, ::Crypto::Curves::SECP384r1, ::Crypto::Curves::SECP521r1> {
-            if (named_curve == "P-256")
+            if (named_curve == "P-256"_utf16)
                 return ::Crypto::Curves::SECP256r1 {};
-            if (named_curve == "P-384")
+            if (named_curve == "P-384"_utf16)
                 return ::Crypto::Curves::SECP384r1 {};
-            if (named_curve == "P-521")
+            if (named_curve == "P-521"_utf16)
                 return ::Crypto::Curves::SECP521r1 {};
             VERIFY_NOT_REACHED();
         }();
@@ -5267,22 +5276,22 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDH::import_key(AlgorithmParams const&
 
         // 7. If params is not an instance of the ECParameters ASN.1 type defined in [RFC5480] that specifies a namedCurve, then throw a DataError.
         // 8. Let namedCurve be a string whose initial value is undefined.
-        String named_curve;
+        NamedCurve named_curve;
 
         // 9. If params is equivalent to the secp256r1 object identifier defined in [RFC5480]:
         if (ec_params == ::Crypto::ASN1::secp256r1_oid) {
             // Set namedCurve to "P-256".
-            named_curve = "P-256"_string;
+            named_curve = "P-256"_utf16;
         }
         // If params is equivalent to the secp384r1 object identifier defined in [RFC5480]:
         else if (ec_params == ::Crypto::ASN1::secp384r1_oid) {
             // Set namedCurve to "P-384".
-            named_curve = "P-384"_string;
+            named_curve = "P-384"_utf16;
         }
         // If params is equivalent to the secp521r1 object identifier defined in [RFC5480]:
         else if (ec_params == ::Crypto::ASN1::secp521r1_oid) {
             // Set namedCurve to "P-521".
-            named_curve = "P-521"_string;
+            named_curve = "P-521"_utf16;
         }
 
         // 10. If namedCurve is not undefined
@@ -5318,11 +5327,11 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDH::import_key(AlgorithmParams const&
         // 12. If the key value is not a valid point on the Elliptic Curve identified
         //     by the namedCurve member of normalizedAlgorithm throw a DataError.
         auto curve = [&named_curve] -> Variant<::Crypto::Curves::SECP256r1, ::Crypto::Curves::SECP384r1, ::Crypto::Curves::SECP521r1> {
-            if (named_curve == "P-256")
+            if (named_curve == "P-256"_utf16)
                 return ::Crypto::Curves::SECP256r1 {};
-            if (named_curve == "P-384")
+            if (named_curve == "P-384"_utf16)
                 return ::Crypto::Curves::SECP384r1 {};
-            if (named_curve == "P-521")
+            if (named_curve == "P-521"_utf16)
                 return ::Crypto::Curves::SECP521r1 {};
             VERIFY_NOT_REACHED();
         }();
@@ -5380,11 +5389,11 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDH::import_key(AlgorithmParams const&
             return WebIDL::SyntaxError::create(m_realm, "Usages must be empty"_utf16);
 
         // 4. If the kty field of jwk is not "EC", then throw a DataError.
-        if (jwk.kty != "EC"sv)
+        if (jwk.kty != "EC"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 5. If usages is non-empty and the use field of jwk is present and is not equal to "enc" then throw a DataError.
-        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"sv)
+        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key use"_utf16);
 
         // 6. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web Key [JWK],
@@ -5406,13 +5415,13 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDH::import_key(AlgorithmParams const&
             return WebIDL::DataError::create(m_realm, "Invalid algorithm"_utf16);
 
         // 10. If namedCurve is "P-256", "P-384" or "P-521":
-        if (named_curve.is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
+        if (named_curve.is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
             size_t coord_size;
-            if (named_curve == "P-256"sv)
+            if (named_curve == "P-256"_utf16)
                 coord_size = 256 / 8;
-            else if (named_curve == "P-384"sv)
+            else if (named_curve == "P-384"_utf16)
                 coord_size = 384 / 8;
-            else if (named_curve == "P-521"sv)
+            else if (named_curve == "P-521"_utf16)
                 coord_size = ceil_div(521, 8);
             else
                 VERIFY_NOT_REACHED();
@@ -5421,7 +5430,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDH::import_key(AlgorithmParams const&
             if (!jwk.x.has_value() || !jwk.y.has_value())
                 return WebIDL::DataError::create(m_realm, "Invalid key"_utf16);
 
-            auto maybe_x_bytes = decode_base64url(jwk.x.value());
+            auto maybe_x_bytes = base64_url_bytes_decode(m_realm, jwk.x.value());
             if (maybe_x_bytes.is_error()) {
                 return WebIDL::DataError::create(m_realm, "Failed to decode base64"_utf16);
             }
@@ -5429,7 +5438,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDH::import_key(AlgorithmParams const&
             if (x_bytes.size() != coord_size)
                 return WebIDL::DataError::create(m_realm, "Invalid key size"_utf16);
 
-            auto maybe_y_bytes = decode_base64url(jwk.y.value());
+            auto maybe_y_bytes = base64_url_bytes_decode(m_realm, jwk.y.value());
             if (maybe_y_bytes.is_error()) {
                 return WebIDL::DataError::create(m_realm, "Failed to decode base64"_utf16);
             }
@@ -5446,7 +5455,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDH::import_key(AlgorithmParams const&
             // If the d field is present:
             if (jwk.d.has_value()) {
                 // 1. If jwk does not meet the requirements of Section 6.2.2 of JSON Web Algorithms [JWA], then throw a DataError.
-                auto maybe_d_bytes = decode_base64url(jwk.d.value());
+                auto maybe_d_bytes = base64_url_bytes_decode(m_realm, jwk.d.value());
                 if (maybe_d_bytes.is_error()) {
                     return WebIDL::DataError::create(m_realm, "Failed to decode base64"_utf16);
                 }
@@ -5485,11 +5494,11 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDH::import_key(AlgorithmParams const&
         // 11. If the key value is not a valid point on the Elliptic Curve identified
         //     by the namedCurve member of normalizedAlgorithm throw a DataError.
         auto curve = [&named_curve] -> Variant<::Crypto::Curves::SECP256r1, ::Crypto::Curves::SECP384r1, ::Crypto::Curves::SECP521r1> {
-            if (named_curve == "P-256")
+            if (named_curve == "P-256"_utf16)
                 return ::Crypto::Curves::SECP256r1 {};
-            if (named_curve == "P-384")
+            if (named_curve == "P-384"_utf16)
                 return ::Crypto::Curves::SECP384r1 {};
-            if (named_curve == "P-521")
+            if (named_curve == "P-521"_utf16)
                 return ::Crypto::Curves::SECP521r1 {};
             VERIFY_NOT_REACHED();
         }();
@@ -5527,7 +5536,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDH::import_key(AlgorithmParams const&
     // For all existing asymmetric algorithms in WebCrypto, "raw-public" acts as an alias of "raw".
     else if (key_format == Bindings::KeyFormat::Raw || key_format == Bindings::KeyFormat::RawPublic) {
         // 1. If the namedCurve member of normalizedAlgorithm is not a named curve, then throw a DataError.
-        if (!normalized_algorithm.named_curve.is_one_of("P-256"sv, "P-384"sv, "P-521"sv))
+        if (!normalized_algorithm.named_curve.is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16))
             return WebIDL::DataError::create(m_realm, "Invalid algorithm"_utf16);
 
         // 2. If usages is not the empty list, then throw a SyntaxError.
@@ -5535,7 +5544,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ECDH::import_key(AlgorithmParams const&
             return WebIDL::SyntaxError::create(m_realm, "Usages must be empty"_utf16);
 
         // 3. If namedCurve is "P-256", "P-384" or "P-521":
-        if (normalized_algorithm.named_curve.is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
+        if (normalized_algorithm.named_curve.is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
             auto key_bytes = move(key_data.get<ByteBuffer>());
 
             // 1. Let Q be the Elliptic Curve public key on the curve identified by the namedCurve
@@ -5602,7 +5611,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDH::export_key(Bindings::KeyFormat fo
         //    Set the subjectPublicKey field to keyData
         //    If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-256", "P-384" or "P-521":
         auto& algorithm = static_cast<EcKeyAlgorithm const&>(*key->algorithm());
-        if (algorithm.named_curve().is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
+        if (algorithm.named_curve().is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
             //  Let keyData be the octet string that represents the Elliptic Curve public key represented by the [[handle]] internal slot
             //  of key according to the encoding rules specified in Section 2.3.3 of [SEC1] and using the uncompressed form.
             //  If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-256":
@@ -5617,11 +5626,11 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDH::export_key(Bindings::KeyFormat fo
                     auto public_key_bytes = TRY(public_key.to_uncompressed());
 
                     Span<int const> ec_params;
-                    if (algorithm.named_curve() == "P-256"sv)
+                    if (algorithm.named_curve() == "P-256"_utf16)
                         ec_params = ::Crypto::ASN1::secp256r1_oid;
-                    else if (algorithm.named_curve() == "P-384"sv)
+                    else if (algorithm.named_curve() == "P-384"_utf16)
                         ec_params = ::Crypto::ASN1::secp384r1_oid;
-                    else if (algorithm.named_curve() == "P-521"sv)
+                    else if (algorithm.named_curve() == "P-521"_utf16)
                         ec_params = ::Crypto::ASN1::secp521r1_oid;
                     else
                         VERIFY_NOT_REACHED();
@@ -5665,7 +5674,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDH::export_key(Bindings::KeyFormat fo
         //      Set the parameters field to an instance of the ECParameters ASN.1 type defined in [RFC5480] as follows:
         //          If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-256", "P-384" or "P-521":
         auto& algorithm = static_cast<EcKeyAlgorithm const&>(*key->algorithm());
-        if (algorithm.named_curve().is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
+        if (algorithm.named_curve().is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
             // Let keyData be the result of DER-encoding an instance of the ECPrivateKey structure defined
             // in Section 3 of [RFC5915] for the Elliptic Curve private key represented by the [[handle]] internal slot
             // of key and that conforms to the following:
@@ -5683,11 +5692,11 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDH::export_key(Bindings::KeyFormat fo
             auto maybe_data = handle.visit(
                 [&](::Crypto::PK::ECPrivateKey const& private_key) -> ErrorOr<ByteBuffer> {
                     Span<int const> ec_params;
-                    if (algorithm.named_curve() == "P-256"sv)
+                    if (algorithm.named_curve() == "P-256"_utf16)
                         ec_params = ::Crypto::ASN1::secp256r1_oid;
-                    else if (algorithm.named_curve() == "P-384"sv)
+                    else if (algorithm.named_curve() == "P-384"_utf16)
                         ec_params = ::Crypto::ASN1::secp384r1_oid;
-                    else if (algorithm.named_curve() == "P-521"sv)
+                    else if (algorithm.named_curve() == "P-521"_utf16)
                         ec_params = ::Crypto::ASN1::secp521r1_oid;
                     else
                         VERIFY_NOT_REACHED();
@@ -5720,46 +5729,46 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDH::export_key(Bindings::KeyFormat fo
         JsonWebKey jwk = {};
 
         // 2. Set the kty attribute of jwk to "EC".
-        jwk.kty = "EC"_string;
+        jwk.kty = "EC"_utf16;
 
         // 3. If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-256", "P-384" or "P-521":
         auto& algorithm = static_cast<EcKeyAlgorithm const&>(*key->algorithm());
-        if (algorithm.named_curve().is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
+        if (algorithm.named_curve().is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
             // 1. If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-256":
-            if (algorithm.named_curve() == "P-256"sv) {
+            if (algorithm.named_curve() == "P-256"_utf16) {
                 // Set the crv attribute of jwk to "P-256"
-                jwk.crv = "P-256"_string;
+                jwk.crv = "P-256"_utf16;
             }
             // If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-384":
-            else if (algorithm.named_curve() == "P-384"sv) {
+            else if (algorithm.named_curve() == "P-384"_utf16) {
                 // Set the crv attribute of jwk to "P-384"
-                jwk.crv = "P-384"_string;
+                jwk.crv = "P-384"_utf16;
             }
             // If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-521":
-            else if (algorithm.named_curve() == "P-521"sv) {
+            else if (algorithm.named_curve() == "P-521"_utf16) {
                 // Set the crv attribute of jwk to "P-521"
-                jwk.crv = "P-521"_string;
+                jwk.crv = "P-521"_utf16;
             }
 
             auto maybe_error = handle.visit(
                 [&](::Crypto::PK::ECPublicKey const& public_key) -> ErrorOr<void> {
                     // 2. Set the x attribute of jwk according to the definition in Section 6.2.1.2 of JSON Web Algorithms [JWA].
                     auto x_bytes = TRY(public_key.x_bytes());
-                    jwk.x = TRY(encode_base64url(x_bytes, AK::OmitPadding::Yes));
+                    jwk.x = TRY(base64_url_bytes_encode(x_bytes));
 
                     // 3. Set the y attribute of jwk according to the definition in Section 6.2.1.3 of JSON Web Algorithms [JWA].
                     auto y_bytes = TRY(public_key.y_bytes());
-                    jwk.y = TRY(encode_base64url(y_bytes, AK::OmitPadding::Yes));
+                    jwk.y = TRY(base64_url_bytes_encode(y_bytes));
 
                     return {};
                 },
                 [&](::Crypto::PK::ECPrivateKey const& private_key) -> ErrorOr<void> {
                     Variant<Empty, ::Crypto::Curves::SECP256r1, ::Crypto::Curves::SECP384r1, ::Crypto::Curves::SECP521r1> curve;
-                    if (algorithm.named_curve() == "P-256"sv)
+                    if (algorithm.named_curve() == "P-256"_utf16)
                         curve = ::Crypto::Curves::SECP256r1 {};
-                    else if (algorithm.named_curve() == "P-384"sv)
+                    else if (algorithm.named_curve() == "P-384"_utf16)
                         curve = ::Crypto::Curves::SECP384r1 {};
-                    else if (algorithm.named_curve() == "P-521"sv)
+                    else if (algorithm.named_curve() == "P-521"_utf16)
                         curve = ::Crypto::Curves::SECP521r1 {};
                     else
                         VERIFY_NOT_REACHED();
@@ -5773,10 +5782,10 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDH::export_key(Bindings::KeyFormat fo
                     auto y_bytes = TRY(public_key.y_bytes());
 
                     // 2. Set the x attribute of jwk according to the definition in Section 6.2.1.2 of JSON Web Algorithms [JWA].
-                    jwk.x = TRY(encode_base64url(x_bytes, AK::OmitPadding::Yes));
+                    jwk.x = TRY(base64_url_bytes_encode(x_bytes));
 
                     // 3. Set the y attribute of jwk according to the definition in Section 6.2.1.3 of JSON Web Algorithms [JWA].
-                    jwk.y = TRY(encode_base64url(y_bytes, AK::OmitPadding::Yes));
+                    jwk.y = TRY(base64_url_bytes_encode(y_bytes));
 
                     return {};
                 },
@@ -5793,7 +5802,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDH::export_key(Bindings::KeyFormat fo
                     [&](::Crypto::PK::ECPrivateKey const& private_key) -> ErrorOr<void> {
                         // Set the d attribute of jwk according to the definition in Section 6.2.2.1 of JSON Web Algorithms [JWA].
                         auto d_bytes = TRY(private_key.d_bytes());
-                        jwk.d = TRY(encode_base64url(d_bytes, AK::OmitPadding::Yes));
+                        jwk.d = TRY(base64_url_bytes_encode(d_bytes));
 
                         return {};
                     },
@@ -5813,7 +5822,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDH::export_key(Bindings::KeyFormat fo
         }
 
         // 4. Set the key_ops attribute of jwk to the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages())
             jwk.key_ops->unchecked_append(idl_enum_to_string(usage));
@@ -5837,7 +5846,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ECDH::export_key(Bindings::KeyFormat fo
 
         // 2. If the namedCurve attribute of the [[algorithm]] internal slot of key is "P-256", "P-384" or "P-521":
         auto& algorithm = static_cast<EcKeyAlgorithm const&>(*key->algorithm());
-        if (algorithm.named_curve().is_one_of("P-256"sv, "P-384"sv, "P-521"sv)) {
+        if (algorithm.named_curve().is_one_of("P-256"_utf16, "P-384"_utf16, "P-521"_utf16)) {
             // Let data be the octet string that represents the Elliptic Curve public key represented by the [[handle]] internal slot
             // of key according to the encoding rules specified in Section 2.3.3 of [SEC1] and using the uncompressed form.
             auto maybe_data = handle.visit(
@@ -6059,11 +6068,11 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ED25519::import_key(
         }
 
         // 3. If the kty field of jwk is not "OKP", then throw a DataError.
-        if (jwk.kty != "OKP"sv)
+        if (jwk.kty != "OKP"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 4. If the crv field of jwk is not "Ed25519", then throw a DataError.
-        if (jwk.crv != "Ed25519"sv)
+        if (jwk.crv != "Ed25519"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid curve"_utf16);
 
         // 5. If the alg field of jwk is present and is not "Ed25519" or "EdDSA", then throw a DataError.
@@ -6071,7 +6080,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ED25519::import_key(
             return WebIDL::DataError::create(m_realm, "Invalid algorithm"_utf16);
 
         // 6. If usages is non-empty and the use field of jwk is present and is not "sig", then throw a DataError.
-        if (!usages.is_empty() && jwk.use.has_value() && jwk.use.value() != "sig")
+        if (!usages.is_empty() && jwk.use.has_value() && jwk.use.value() != "sig"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key usage"_utf16);
 
         // 7. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web Key [JWK],
@@ -6087,12 +6096,12 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ED25519::import_key(
             // 1. If jwk does not meet the requirements of the JWK private key format described in Section 2 of [RFC8037],
             //    then throw a DataError.
             // o  The parameter "kty" MUST be "OKP".
-            if (jwk.kty != "OKP"sv)
+            if (jwk.kty != "OKP"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
             // https://www.iana.org/assignments/jose/jose.xhtml#web-key-elliptic-curve
             // o  The parameter "crv" MUST be present and contain the subtype of the key (from the "JSON Web Elliptic Curve" registry).
-            if (jwk.crv != "Ed25519"sv)
+            if (jwk.crv != "Ed25519"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid curve"_utf16);
 
             // o  The parameter "x" MUST be present and contain the public key encoded using the base64url [RFC4648] encoding.
@@ -6125,12 +6134,12 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ED25519::import_key(
         else {
             // 1. If jwk does not meet the requirements of the JWK public key format described in Section 2 of [RFC8037], then throw a DataError.
             // o  The parameter "kty" MUST be "OKP".
-            if (jwk.kty != "OKP"sv)
+            if (jwk.kty != "OKP"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
             // https://www.iana.org/assignments/jose/jose.xhtml#web-key-elliptic-curve
             // o  The parameter "crv" MUST be present and contain the subtype of the key (from the "JSON Web Elliptic Curve" registry).
-            if (jwk.crv != "Ed25519"sv)
+            if (jwk.crv != "Ed25519"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid curve"_utf16);
 
             // o  The parameter "x" MUST be present and contain the public key encoded using the base64url [RFC4648] encoding.
@@ -6262,17 +6271,17 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ED25519::export_key(Bindings::KeyFormat
         JsonWebKey jwk;
 
         // 2. Set the kty attribute of jwk to "OKP".
-        jwk.kty = "OKP"_string;
+        jwk.kty = "OKP"_utf16;
 
         // 3. Set the alg attribute of jwk to "Ed25519".
-        jwk.alg = "Ed25519"_string;
+        jwk.alg = "Ed25519"_utf16;
 
         // 4. Set the crv attribute of jwk to "Ed25519".
-        jwk.crv = "Ed25519"_string;
+        jwk.crv = "Ed25519"_utf16;
 
         // 5. Set the x attribute of jwk according to the definition in Section 2 of [RFC8037].
         if (key->type() == Bindings::KeyType::Public) {
-            jwk.x = TRY_OR_THROW_OOM(vm, encode_base64url(key_data, AK::OmitPadding::Yes));
+            jwk.x = TRY_OR_THROW_OOM(vm, base64_url_bytes_encode(key_data));
         } else {
             // The "x" parameter of the "epk" field is set as follows:
             // Apply the appropriate ECDH function to the ephemeral private key (as scalar input)
@@ -6280,17 +6289,17 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ED25519::export_key(Bindings::KeyFormat
             // The base64url encoding of the output is the value for the "x" parameter of the "epk" field.
             ::Crypto::Curves::Ed25519 curve;
             auto public_key = TRY_OR_THROW_OOM(vm, curve.generate_public_key(key_data));
-            jwk.x = TRY_OR_THROW_OOM(vm, encode_base64url(public_key, AK::OmitPadding::Yes));
+            jwk.x = TRY_OR_THROW_OOM(vm, base64_url_bytes_encode(public_key));
         }
 
         // 6. If the [[type]] internal slot of key is "private"
         if (key->type() == Bindings::KeyType::Private) {
             // 1. Set the d attribute of jwk according to the definition in Section 2 of [RFC8037].
-            jwk.d = TRY_OR_THROW_OOM(vm, encode_base64url(key_data, AK::OmitPadding::Yes));
+            jwk.d = TRY_OR_THROW_OOM(vm, base64_url_bytes_encode(key_data));
         }
 
         // 7. Set the key_ops attribute of jwk to the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages())
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
@@ -6573,19 +6582,19 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ED448::import_key(
         }
 
         // 3. If the kty field of jwk is not "OKP", then throw a DataError.
-        if (jwk.kty != "OKP"sv)
+        if (jwk.kty != "OKP"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 4. If the crv field of jwk is not "Ed448", then throw a DataError.
-        if (jwk.crv != "Ed448"sv)
+        if (jwk.crv != "Ed448"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid curve"_utf16);
 
         // 5. If the alg field of jwk is present and is not "Ed448" or "EdDSA", then throw a DataError.
-        if (jwk.alg.has_value() && (jwk.alg.value() != "Ed448"sv && jwk.alg.value() != "EdDSA"sv))
+        if (jwk.alg.has_value() && (jwk.alg.value() != "Ed448"_utf16 && jwk.alg.value() != "EdDSA"_utf16))
             return WebIDL::DataError::create(m_realm, "Invalid algorithm"_utf16);
 
         // 6. If usages is non-empty and the use field of jwk is present and is not "sig", then throw a DataError.
-        if (!usages.is_empty() && jwk.use.has_value() && jwk.use.value() != "sig")
+        if (!usages.is_empty() && jwk.use.has_value() && jwk.use.value() != "sig"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key usage"_utf16);
 
         // 7. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web Key [JWK],
@@ -6601,12 +6610,12 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ED448::import_key(
             // 1. If jwk does not meet the requirements of the JWK private key format described in Section 2 of [RFC8037],
             //    then throw a DataError.
             // o  The parameter "kty" MUST be "OKP".
-            if (jwk.kty != "OKP"sv)
+            if (jwk.kty != "OKP"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
             // https://www.iana.org/assignments/jose/jose.xhtml#web-key-elliptic-curve
             // o  The parameter "crv" MUST be present and contain the subtype of the key (from the "JSON Web Elliptic Curve" registry).
-            if (jwk.crv != "Ed448"sv)
+            if (jwk.crv != "Ed448"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid curve"_utf16);
 
             // o  The parameter "x" MUST be present and contain the public key encoded using the base64url [RFC4648] encoding.
@@ -6639,12 +6648,12 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ED448::import_key(
         else {
             // 1. If jwk does not meet the requirements of the JWK public key format described in Section 2 of [RFC8037], then throw a DataError.
             // o  The parameter "kty" MUST be "OKP".
-            if (jwk.kty != "OKP"sv)
+            if (jwk.kty != "OKP"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
             // https://www.iana.org/assignments/jose/jose.xhtml#web-key-elliptic-curve
             // o  The parameter "crv" MUST be present and contain the subtype of the key (from the "JSON Web Elliptic Curve" registry).
-            if (jwk.crv != "Ed448"sv)
+            if (jwk.crv != "Ed448"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid curve"_utf16);
 
             // o  The parameter "x" MUST be present and contain the public key encoded using the base64url [RFC4648] encoding.
@@ -6774,17 +6783,17 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ED448::export_key(Bindings::KeyFormat f
         JsonWebKey jwk;
 
         // 2. Set the kty attribute of jwk to "OKP".
-        jwk.kty = "OKP"_string;
+        jwk.kty = "OKP"_utf16;
 
         // 3. Set the alg attribute of jwk to "Ed448".
-        jwk.alg = "Ed448"_string;
+        jwk.alg = "Ed448"_utf16;
 
         // 4. Set the crv attribute of jwk to "Ed448".
-        jwk.crv = "Ed448"_string;
+        jwk.crv = "Ed448"_utf16;
 
         // 5. Set the x attribute of jwk according to the definition in Section 2 of [RFC8037].
         if (key->type() == Bindings::KeyType::Public) {
-            jwk.x = TRY_OR_THROW_OOM(vm, encode_base64url(key_data, AK::OmitPadding::Yes));
+            jwk.x = TRY_OR_THROW_OOM(vm, base64_url_bytes_encode(key_data));
         } else {
             // The "x" parameter of the "epk" field is set as follows:
             // Apply the appropriate ECDH function to the ephemeral private key (as scalar input)
@@ -6792,17 +6801,17 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ED448::export_key(Bindings::KeyFormat f
             // The base64url encoding of the output is the value for the "x" parameter of the "epk" field.
             ::Crypto::Curves::Ed448 curve;
             auto public_key = TRY_OR_THROW_OOM(vm, curve.generate_public_key(key_data));
-            jwk.x = TRY_OR_THROW_OOM(vm, encode_base64url(public_key, AK::OmitPadding::Yes));
+            jwk.x = TRY_OR_THROW_OOM(vm, base64_url_bytes_encode(public_key));
         }
 
         // 6. If the [[type]] internal slot of key is "private"
         if (key->type() == Bindings::KeyType::Private) {
             // 1. Set the d attribute of jwk according to the definition in Section 2 of [RFC8037].
-            jwk.d = TRY_OR_THROW_OOM(vm, encode_base64url(key_data, AK::OmitPadding::Yes));
+            jwk.d = TRY_OR_THROW_OOM(vm, base64_url_bytes_encode(key_data));
         }
 
         // 7. Set the key_ops attribute of jwk to the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages())
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
@@ -7313,15 +7322,15 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> X25519::import_key([[maybe_unused]] Web:
             return WebIDL::SyntaxError::create(m_realm, "Usages must be empty if d is missing"_utf16);
 
         // 4. If the kty field of jwk is not "OKP", then throw a DataError.
-        if (jwk.kty != "OKP"sv)
+        if (jwk.kty != "OKP"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 5. If the crv field of jwk is not "X25519", then throw a DataError.
-        if (jwk.crv != "X25519"sv)
+        if (jwk.crv != "X25519"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid curve"_utf16);
 
         // 6. If usages is non-empty and the use field of jwk is present and is not equal to "enc" then throw a DataError.
-        if (!usages.is_empty() && jwk.use.has_value() && jwk.use.value() != "enc"sv)
+        if (!usages.is_empty() && jwk.use.has_value() && jwk.use.value() != "enc"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid use"_utf16);
 
         // 7. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web Key [JWK],
@@ -7336,12 +7345,12 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> X25519::import_key([[maybe_unused]] Web:
         if (jwk.d.has_value()) {
             // 1. If jwk does not meet the requirements of the JWK private key format described in Section 2 of [RFC8037], then throw a DataError.
             // o  The parameter "kty" MUST be "OKP".
-            if (jwk.kty != "OKP"sv)
+            if (jwk.kty != "OKP"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
             // https://www.iana.org/assignments/jose/jose.xhtml#web-key-elliptic-curve
             // o  The parameter "crv" MUST be present and contain the subtype of the key (from the "JSON Web Elliptic Curve" registry).
-            if (jwk.crv != "X25519"sv)
+            if (jwk.crv != "X25519"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid curve"_utf16);
 
             // o  The parameter "x" MUST be present and contain the public key encoded using the base64url [RFC4648] encoding.
@@ -7374,12 +7383,12 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> X25519::import_key([[maybe_unused]] Web:
         else {
             // 1. If jwk does not meet the requirements of the JWK public key format described in Section 2 of [RFC8037], then throw a DataError.
             // o  The parameter "kty" MUST be "OKP".
-            if (jwk.kty != "OKP"sv)
+            if (jwk.kty != "OKP"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
             // https://www.iana.org/assignments/jose/jose.xhtml#web-key-elliptic-curve
             // o  The parameter "crv" MUST be present and contain the subtype of the key (from the "JSON Web Elliptic Curve" registry).
-            if (jwk.crv != "X25519"sv)
+            if (jwk.crv != "X25519"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid curve"_utf16);
 
             // o  The parameter "x" MUST be present and contain the public key encoded using the base64url [RFC4648] encoding.
@@ -7509,15 +7518,15 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> X25519::export_key(Bindings::KeyFormat
         JsonWebKey jwk = {};
 
         // 2. Set the kty attribute of jwk to "OKP".
-        jwk.kty = "OKP"_string;
+        jwk.kty = "OKP"_utf16;
 
         // 3. Set the crv attribute of jwk to "X25519".
-        jwk.crv = "X25519"_string;
+        jwk.crv = "X25519"_utf16;
 
         // 4. Set the x attribute of jwk according to the definition in Section 2 of [RFC8037].
         if (key->type() == Bindings::KeyType::Public) {
             auto public_key = handle.get<ByteBuffer>();
-            jwk.x = TRY_OR_THROW_OOM(vm, encode_base64url(public_key, AK::OmitPadding::Yes));
+            jwk.x = TRY_OR_THROW_OOM(vm, base64_url_bytes_encode(public_key));
         } else {
             // The "x" parameter of the "epk" field is set as follows:
             // Apply the appropriate ECDH function to the ephemeral private key (as scalar input)
@@ -7525,18 +7534,18 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> X25519::export_key(Bindings::KeyFormat
             // The base64url encoding of the output is the value for the "x" parameter of the "epk" field.
             ::Crypto::Curves::X25519 curve;
             auto public_key = TRY_OR_THROW_OOM(vm, curve.generate_public_key(handle.get<ByteBuffer>()));
-            jwk.x = TRY_OR_THROW_OOM(vm, encode_base64url(public_key, AK::OmitPadding::Yes));
+            jwk.x = TRY_OR_THROW_OOM(vm, base64_url_bytes_encode(public_key));
         }
 
         // 5. If the [[type]] internal slot of key is "private"
         if (key->type() == Bindings::KeyType::Private) {
             // 1. Set the d attribute of jwk according to the definition in Section 2 of [RFC8037].
             auto private_key = handle.get<ByteBuffer>();
-            jwk.d = TRY_OR_THROW_OOM(vm, encode_base64url(private_key, AK::OmitPadding::Yes));
+            jwk.d = TRY_OR_THROW_OOM(vm, base64_url_bytes_encode(private_key));
         }
 
         // 6. Set the key_ops attribute of jwk to the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages())
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
@@ -7762,28 +7771,28 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> X448::export_key(Bindings::KeyFormat fo
         JsonWebKey jwk = {};
 
         // 2. Set the kty attribute of jwk to "OKP".
-        jwk.kty = "OKP"_string;
+        jwk.kty = "OKP"_utf16;
 
         // 3. Set the crv attribute of jwk to "X448".
-        jwk.crv = "X448"_string;
+        jwk.crv = "X448"_utf16;
 
         // 4. Set the x attribute of jwk according to the definition in Section 2 of [RFC8037].
         if (key->type() == Bindings::KeyType::Public) {
-            jwk.x = TRY_OR_THROW_OOM(m_realm->vm(), encode_base64url(key_data, AK::OmitPadding::Yes));
+            jwk.x = TRY_OR_THROW_OOM(m_realm->vm(), base64_url_bytes_encode(key_data));
         } else {
             ::Crypto::Curves::X448 curve;
             auto public_key = TRY_OR_THROW_OOM(m_realm->vm(), curve.generate_public_key(key_data));
-            jwk.x = TRY_OR_THROW_OOM(m_realm->vm(), encode_base64url(public_key, AK::OmitPadding::Yes));
+            jwk.x = TRY_OR_THROW_OOM(m_realm->vm(), base64_url_bytes_encode(public_key));
         }
 
         // 5. If the [[type]] internal slot of key is "private"
         if (key->type() == Bindings::KeyType::Private) {
             // 1. Set the d attribute of jwk according to the definition in Section 2 of [RFC8037].
-            jwk.d = TRY_OR_THROW_OOM(m_realm->vm(), encode_base64url(key_data, AK::OmitPadding::Yes));
+            jwk.d = TRY_OR_THROW_OOM(m_realm->vm(), base64_url_bytes_encode(key_data));
         }
 
         // 6. Set the key_ops attribute of jwk to the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages())
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
@@ -7932,15 +7941,15 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> X448::import_key(
             return WebIDL::SyntaxError::create(m_realm, "Usages must be empty"_utf16);
 
         // 4. If the kty field of jwk is not "OKP", then throw a DataError.
-        if (jwk.kty != "OKP"sv)
+        if (jwk.kty != "OKP"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 5. If the crv field of jwk is not "X448", then throw a DataError.
-        if (jwk.crv != "X448"sv)
+        if (jwk.crv != "X448"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid curve"_utf16);
 
         // 6. If usages is non-empty and the use field of jwk is present and is not equal to "enc" then throw a DataError.
-        if (!usages.is_empty() && jwk.use.has_value() && jwk.use.value() != "enc"sv)
+        if (!usages.is_empty() && jwk.use.has_value() && jwk.use.value() != "enc"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid use"_utf16);
 
         // 7. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web Key [JWK],
@@ -7958,12 +7967,12 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> X448::import_key(
             // 1. If jwk does not meet the requirements of the JWK private key format described in Section 2 of [RFC8037], then throw a DataError.
 
             // o  The parameter "kty" MUST be "OKP".
-            if (jwk.kty != "OKP"sv)
+            if (jwk.kty != "OKP"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
             // https://www.iana.org/assignments/jose/jose.xhtml#web-key-elliptic-curve
             // o  The parameter "crv" MUST be present and contain the subtype of the key (from the "JSON Web Elliptic Curve" registry).
-            if (jwk.crv != "X448"sv)
+            if (jwk.crv != "X448"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid curve"_utf16);
 
             // o  The parameter "x" MUST be present and contain the public key encoded using the base64url [RFC4648] encoding.
@@ -7996,12 +8005,12 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> X448::import_key(
         else {
             // 1. If jwk does not meet the requirements of the JWK public key format described in Section 2 of [RFC8037], then throw a DataError.
             // o  The parameter "kty" MUST be "OKP".
-            if (jwk.kty != "OKP"sv)
+            if (jwk.kty != "OKP"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
             // https://www.iana.org/assignments/jose/jose.xhtml#web-key-elliptic-curve
             // o  The parameter "crv" MUST be present and contain the subtype of the key (from the "JSON Web Elliptic Curve" registry).
-            if (jwk.crv != "X448"sv)
+            if (jwk.crv != "X448"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid curve"_utf16);
 
             // o  The parameter "x" MUST be present and contain the public key encoded using the base64url [RFC4648] encoding.
@@ -8247,7 +8256,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> HMAC::import_key(Web::Crypto::AlgorithmP
         auto& jwk = key_data.get<JsonWebKey>();
 
         // 2. If the kty field of jwk is not "oct", then throw a DataError.
-        if (jwk.kty != "oct"sv)
+        if (jwk.kty != "oct"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 3. If jwk does not meet the requirements of Section 6.4 of JSON Web Algorithms [JWA],
@@ -8262,28 +8271,28 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> HMAC::import_key(Web::Crypto::AlgorithmP
         auto hash_name = hash->name();
         if (hash_name == "SHA-1") {
             // If the alg field of jwk is present and is not "HS1", then throw a DataError.
-            if (jwk.alg.has_value() && jwk.alg != "HS1"sv)
+            if (jwk.alg.has_value() && *jwk.alg != "HS1"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid algorithm"_utf16);
         }
 
         // If the name attribute of hash is "SHA-256":
         else if (hash_name == "SHA-256") {
             // If the alg field of jwk is present and is not "HS256", then throw a DataError.
-            if (jwk.alg.has_value() && jwk.alg != "HS256"sv)
+            if (jwk.alg.has_value() && *jwk.alg != "HS256"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid algorithm"_utf16);
         }
 
         // If the name attribute of hash is "SHA-384":
         else if (hash_name == "SHA-384") {
             // If the alg field of jwk is present and is not "HS384", then throw a DataError.
-            if (jwk.alg.has_value() && jwk.alg != "HS384"sv)
+            if (jwk.alg.has_value() && *jwk.alg != "HS384"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid algorithm"_utf16);
         }
 
         // If the name attribute of hash is "SHA-512":
         else if (hash_name == "SHA-512") {
             // If the alg field of jwk is present and is not "HS512", then throw a DataError.
-            if (jwk.alg.has_value() && jwk.alg != "HS512"sv)
+            if (jwk.alg.has_value() && *jwk.alg != "HS512"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid algorithm"_utf16);
         }
 
@@ -8296,7 +8305,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> HMAC::import_key(Web::Crypto::AlgorithmP
 
         // 7. If usages is non-empty and the use field of jwk is present and is not "sign", then
         //    throw a DataError.
-        if (!usages.is_empty() && jwk.use.has_value() && jwk.use != "sign"sv)
+        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "sign"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid use in JsonWebKey"_utf16);
 
         // 8. If the key_ops field of jwk is present, and is invalid according to the requirements
@@ -8397,11 +8406,11 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> HMAC::export_key(Bindings::KeyFormat fo
         JsonWebKey jwk {};
 
         // Set the kty attribute of jwk to the string "oct".
-        jwk.kty = "oct"_string;
+        jwk.kty = "oct"_utf16;
 
         // Set the k attribute of jwk to be a string containing data, encoded according to Section
         // 6.4 of JSON Web Algorithms [JWA].
-        jwk.k = MUST(encode_base64url(data, AK::OmitPadding::Yes));
+        jwk.k = MUST(base64_url_bytes_encode(data));
 
         // Let algorithm be the [[algorithm]] internal slot of key.
         auto const& algorithm = as<HmacKeyAlgorithm>(*key->algorithm());
@@ -8413,22 +8422,22 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> HMAC::export_key(Bindings::KeyFormat fo
         auto hash_name = hash->name();
         if (hash_name == "SHA-1") {
             // Set the alg attribute of jwk to the string "HS1".
-            jwk.alg = "HS1"_string;
+            jwk.alg = "HS1"_utf16;
         }
         // If the name attribute of hash is "SHA-256":
         else if (hash_name == "SHA-256") {
             // Set the alg attribute of jwk to the string "HS256".
-            jwk.alg = "HS256"_string;
+            jwk.alg = "HS256"_utf16;
         }
         // If the name attribute of hash is "SHA-384":
         else if (hash_name == "SHA-384") {
             // Set the alg attribute of jwk to the string "HS384".
-            jwk.alg = "HS384"_string;
+            jwk.alg = "HS384"_utf16;
         }
         // If the name attribute of hash is "SHA-512":
         else if (hash_name == "SHA-512") {
             // Set the alg attribute of jwk to the string "HS512".
-            jwk.alg = "HS512"_string;
+            jwk.alg = "HS512"_utf16;
         }
 
         // Otherwise, the name attribute of hash is defined in another applicable
@@ -8441,7 +8450,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> HMAC::export_key(Bindings::KeyFormat fo
         }
 
         // Set the key_ops attribute of jwk to equal the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages()) {
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
@@ -8868,15 +8877,15 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> MLDSA::import_key(AlgorithmParams const&
         }
 
         // 3. If the kty field of jwk is not "AKP", then throw a DataError.
-        if (jwk->kty != "AKP"_string)
+        if (jwk->kty != "AKP"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 4. If the alg field of jwk is not equal to the name member of normalizedAlgorithm, then throw a DataError.
-        if (jwk->alg != params.name)
+        if (!jwk->alg.has_value() || *jwk->alg != params.name.bytes_as_string_view())
             return WebIDL::DataError::create(m_realm, "Invalid algorithm"_utf16);
 
         // 5. If usages is non-empty and the use field of jwk is present and is not equal to "sig", then throw a DataError.
-        if (!usages.is_empty() && jwk->use.has_value() && jwk->use == "sig"_string)
+        if (!usages.is_empty() && jwk->use.has_value() && *jwk->use == "sig"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid usage type"_utf16);
 
         // 6. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web
@@ -9086,29 +9095,23 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> MLDSA::export_key(Bindings::KeyFormat f
         auto jwk = JsonWebKey {};
 
         // 2. Set the kty attribute of jwk to "AKP".
-        jwk.kty = "AKP"_string;
+        jwk.kty = "AKP"_utf16;
 
         // 3. Set the alg attribute of jwk to the name member of normalizedAlgorithm.
-        jwk.alg = key->algorithm_name();
+        jwk.alg = Utf16String::from_ascii_without_validation(key->algorithm_name().bytes_as_string_view().bytes());
 
         // 4. Set the pub attribute of jwk to the base64url encoded public key corresponding to the [[handle]] internal slot of key.
-        jwk.pub = TRY_OR_THROW_OOM(
-            vm,
-            encode_base64url(handle.visit(
-                                 [](::Crypto::PK::MLDSAPublicKey const& public_key) -> ReadonlyBytes { return public_key.public_key(); },
-                                 [](::Crypto::PK::MLDSAPrivateKey const& private_key) -> ReadonlyBytes { return private_key.public_key(); },
-                                 [](auto) -> ReadonlyBytes { VERIFY_NOT_REACHED(); }),
-                AK::OmitPadding::Yes));
+        jwk.pub = TRY_OR_THROW_OOM(vm, base64_url_bytes_encode(handle.visit([](::Crypto::PK::MLDSAPublicKey const& public_key) -> ReadonlyBytes { return public_key.public_key(); }, [](::Crypto::PK::MLDSAPrivateKey const& private_key) -> ReadonlyBytes { return private_key.public_key(); }, [](auto) -> ReadonlyBytes { VERIFY_NOT_REACHED(); })));
 
         // 5. -> If the [[type]] internal slot of key is "private":
         //       Set the priv attribute of jwk to the base64url encoded seed represented by the [[handle]] internal slot of key.
         if (key->type() == Bindings::KeyType::Private) {
             VERIFY(handle.has<::Crypto::PK::MLDSAPrivateKey>());
-            jwk.priv = TRY_OR_THROW_OOM(vm, encode_base64url(handle.get<::Crypto::PK::MLDSAPrivateKey>().seed(), AK::OmitPadding::Yes));
+            jwk.priv = TRY_OR_THROW_OOM(vm, base64_url_bytes_encode(handle.get<::Crypto::PK::MLDSAPrivateKey>().seed()));
         }
 
         // 6. Set the key_ops attribute of jwk to the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages()) {
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
@@ -10002,7 +10005,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ChaCha20Poly1305::import_key(AlgorithmPa
         auto const& jwk = key_data.get<JsonWebKey>();
 
         // 2. If the kty field of jwk is not "oct", then throw a DataError.
-        if (jwk.kty != "oct"_string)
+        if (jwk.kty != "oct"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 3. If jwk does not meet the requirements of Section 6.4 of JSON Web Algorithms [JWA], then throw a DataError.
@@ -10014,11 +10017,11 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> ChaCha20Poly1305::import_key(AlgorithmPa
         data = TRY(parse_jwk_symmetric_key(m_realm, jwk));
 
         // 5. If the alg field of jwk is present, and is not "C20P", then throw a DataError.
-        if (jwk.alg.has_value() && jwk.alg.value() != "C20P"_string)
+        if (jwk.alg.has_value() && jwk.alg.value() != "C20P"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid alg field"_utf16);
 
         // 6. If usages is non-empty and the use field of jwk is present and is not "enc", then throw a DataError.
-        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"_string)
+        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid use field"_utf16);
 
         // 7. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web Key [JWK]
@@ -10076,18 +10079,18 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> ChaCha20Poly1305::export_key(Bindings::
         JsonWebKey jwk = {};
 
         // 2. Set the kty attribute of jwk to the string "oct".
-        jwk.kty = "oct"_string;
+        jwk.kty = "oct"_utf16;
 
         // 3. Set the k attribute of jwk to be a string containing the raw octets of the key represented by [[handle]] internal slot of key,
         //    encoded according to Section 6.4 of JSON Web Algorithms [JWA].
         auto const& key_bytes = key->handle().get<ByteBuffer>();
-        jwk.k = TRY_OR_THROW_OOM(m_realm->vm(), encode_base64url(key_bytes, AK::OmitPadding::Yes));
+        jwk.k = TRY_OR_THROW_OOM(m_realm->vm(), base64_url_bytes_encode(key_bytes));
 
         // 4. Set the alg attribute of jwk to the string "C20P".
-        jwk.alg = "C20P"_string;
+        jwk.alg = "C20P"_utf16;
 
         // 5. Set the key_ops attribute of jwk to the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages()) {
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
@@ -10308,7 +10311,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> AesOcb::import_key(AlgorithmParams const
         auto const& jwk = key_data.get<JsonWebKey>();
 
         // 2. If the kty field of jwk is not "oct", then throw a DataError.
-        if (jwk.kty != "oct"_string)
+        if (jwk.kty != "oct"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 3. If jwk does not meet the requirements of Section 6.4 of JSON Web Algorithms [JWA], then throw a DataError.
@@ -10330,20 +10333,20 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> AesOcb::import_key(AlgorithmParams const
         auto data_bits = data.size() * 8;
         auto const& alg = jwk.alg;
         if (data_bits == 128) {
-            if (alg.has_value() && alg != "A128OCB")
+            if (alg.has_value() && *alg != "A128OCB"_utf16)
                 return WebIDL::DataError::create(m_realm, "Contradictory key size: key has 128 bits, but alg specifies non-128-bit algorithm"_utf16);
         } else if (data_bits == 192) {
-            if (alg.has_value() && alg != "A192OCB")
+            if (alg.has_value() && *alg != "A192OCB"_utf16)
                 return WebIDL::DataError::create(m_realm, "Contradictory key size: key has 192 bits, but alg specifies non-192-bit algorithm"_utf16);
         } else if (data_bits == 256) {
-            if (alg.has_value() && alg != "A256OCB")
+            if (alg.has_value() && *alg != "A256OCB"_utf16)
                 return WebIDL::DataError::create(m_realm, "Contradictory key size: key has 256 bits, but alg specifies non-256-bit algorithm"_utf16);
         } else {
             return WebIDL::DataError::create(m_realm, Utf16String::formatted("Invalid key size: {} bits", data_bits));
         }
 
         // 6. If usages is non-empty and the use field of jwk is present and is not "enc", then throw a DataError.
-        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"_string)
+        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "enc"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid use field"_utf16);
 
         // 7. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web Key [JWK]
@@ -10407,12 +10410,12 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> AesOcb::export_key(Bindings::KeyFormat
         JsonWebKey jwk = {};
 
         // 2. Set the kty attribute of jwk to the string "oct".
-        jwk.kty = "oct"_string;
+        jwk.kty = "oct"_utf16;
 
         // 3. Set the k attribute of jwk to be a string containing the raw octets of the key represented by [[handle]] internal slot of key,
         //    encoded according to Section 6.4 of JSON Web Algorithms [JWA].
         auto const& key_bytes = key->handle().get<ByteBuffer>();
-        jwk.k = TRY_OR_THROW_OOM(m_realm->vm(), encode_base64url(key_bytes, AK::OmitPadding::Yes));
+        jwk.k = TRY_OR_THROW_OOM(m_realm->vm(), base64_url_bytes_encode(key_bytes));
 
         // 4. -> If the length attribute of key is 128:
         //        Set the alg attribute of jwk to the string "A128OCB".
@@ -10422,15 +10425,15 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> AesOcb::export_key(Bindings::KeyFormat
         //        Set the alg attribute of jwk to the string "A256OCB".
         auto key_bits = key_bytes.size() * 8;
         if (key_bits == 128) {
-            jwk.alg = "A128OCB"_string;
+            jwk.alg = "A128OCB"_utf16;
         } else if (key_bits == 192) {
-            jwk.alg = "A192OCB"_string;
+            jwk.alg = "A192OCB"_utf16;
         } else if (key_bits == 256) {
-            jwk.alg = "A256OCB"_string;
+            jwk.alg = "A256OCB"_utf16;
         }
 
         // 5. Set the key_ops attribute of jwk to the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages()) {
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
@@ -10645,7 +10648,7 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> KMAC::import_key(AlgorithmParams const&
         auto const& jwk = key_data.get<JsonWebKey>();
 
         // 2. If the kty field of jwk is not "oct", then throw a DataError.
-        if (jwk.kty != "oct"sv)
+        if (jwk.kty != "oct"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid key type"_utf16);
 
         // 3. If jwk does not meet the requirements of Section 6.4 of JSON Web Algorithms [JWA], then throw a DataError.
@@ -10660,15 +10663,15 @@ WebIDL::ExceptionOr<GC::Ref<CryptoKey>> KMAC::import_key(AlgorithmParams const&
         //           If the alg field of jwk is present and is not "K256", then throw a DataError.
         auto const& algorithm_name = normalized_algorithm.name;
         if (algorithm_name == "KMAC128"sv) {
-            if (jwk.alg.has_value() && *jwk.alg != "K128"sv)
+            if (jwk.alg.has_value() && *jwk.alg != "K128"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid alg field for KMAC128"_utf16);
         } else if (algorithm_name == "KMAC256"sv) {
-            if (jwk.alg.has_value() && *jwk.alg != "K256"sv)
+            if (jwk.alg.has_value() && *jwk.alg != "K256"_utf16)
                 return WebIDL::DataError::create(m_realm, "Invalid alg field for KMAC256"_utf16);
         }
 
         // 6. If usages is non-empty and the use field of jwk is present and is not "sign", then throw a DataError.
-        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "sign"sv)
+        if (!usages.is_empty() && jwk.use.has_value() && *jwk.use != "sign"_utf16)
             return WebIDL::DataError::create(m_realm, "Invalid use in JsonWebKey"_utf16);
 
         // 7. If the key_ops field of jwk is present, and is invalid according to the requirements of JSON Web Key [JWK]
@@ -10751,12 +10754,12 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> KMAC::export_key(Bindings::KeyFormat fo
         JsonWebKey jwk = {};
 
         // 2. Set the kty attribute of jwk to the string "oct".
-        jwk.kty = "oct"_string;
+        jwk.kty = "oct"_utf16;
 
         // 3. Set the k attribute of jwk to be a string containing the raw bits of the key represented by [[handle]] internal slot of key,
         //    encoded according to JSON Web Algorithms [JWA].
         auto const& key_bytes = key->handle().get<ByteBuffer>();
-        jwk.k = TRY_OR_THROW_OOM(m_realm->vm(), encode_base64url(key_bytes, AK::OmitPadding::Yes));
+        jwk.k = TRY_OR_THROW_OOM(m_realm->vm(), base64_url_bytes_encode(key_bytes));
 
         // 4. Let keyAlgorithm be the [[algorithm]] internal slot of key.
         // 5. -> If the name member of keyAlgorithm is "KMAC128":
@@ -10765,13 +10768,13 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> KMAC::export_key(Bindings::KeyFormat fo
         //        Set the alg attribute of jwk to the string "K256".
         auto const& algorithm_name = key->algorithm_name();
         if (algorithm_name == "KMAC128"_string) {
-            jwk.alg = "K128"_string;
+            jwk.alg = "K128"_utf16;
         } else if (algorithm_name == "KMAC256"_string) {
-            jwk.alg = "K256"_string;
+            jwk.alg = "K256"_utf16;
         }
 
         // 6. Set the key_ops attribute of jwk to equal the usages attribute of key.
-        jwk.key_ops = Vector<String> {};
+        jwk.key_ops = Vector<Utf16String> {};
         jwk.key_ops->ensure_capacity(key->internal_usages().size());
         for (auto const& usage : key->internal_usages()) {
             jwk.key_ops->unchecked_append(Bindings::idl_enum_to_string(usage));
diff --git a/Libraries/LibWeb/Crypto/CryptoAlgorithms.h b/Libraries/LibWeb/Crypto/CryptoAlgorithms.h
index a168e24639..a36d29fea6 100644
--- a/Libraries/LibWeb/Crypto/CryptoAlgorithms.h
+++ b/Libraries/LibWeb/Crypto/CryptoAlgorithms.h
@@ -10,6 +10,7 @@
 
 #include <AK/EnumBits.h>
 #include <AK/String.h>
+#include <AK/Utf16String.h>
 #include <LibCrypto/BigInt/UnsignedBigInteger.h>
 #include <LibGC/Ptr.h>
 #include <LibJS/Forward.h>
@@ -23,7 +24,7 @@
 namespace Web::Crypto {
 
 using AlgorithmIdentifier = Variant<GC::Ref<JS::Object>, String>;
-using NamedCurve = String;
+using NamedCurve = Utf16String;
 using KeyDataType = FlattenVariant<WebIDL::BufferSourceVariant, Variant<JsonWebKey>>;
 
 // https://wicg.github.io/webcrypto-modern-algos/#encapsulation
@@ -767,12 +768,12 @@ struct EcdhKeyDeriveParams : public AlgorithmParams {
 struct EcKeyImportParams : public AlgorithmParams {
     virtual ~EcKeyImportParams() override;
 
-    EcKeyImportParams(String named_curve)
+    EcKeyImportParams(NamedCurve named_curve)
         : named_curve(move(named_curve))
     {
     }
 
-    String named_curve;
+    NamedCurve named_curve;
 
     static JS::ThrowCompletionOr<NonnullOwnPtr<AlgorithmParams>> from_value(JS::VM&, JS::Value);
 };
@@ -955,8 +956,8 @@ private:
     }
 };
 
-ErrorOr<String> base64_url_uint_encode(::Crypto::UnsignedBigInteger);
-WebIDL::ExceptionOr<ByteBuffer> base64_url_bytes_decode(JS::Realm&, String const& base64_url_string);
-WebIDL::ExceptionOr<::Crypto::UnsignedBigInteger> base64_url_uint_decode(JS::Realm&, String const& base64_url_string);
+ErrorOr<Utf16String> base64_url_uint_encode(::Crypto::UnsignedBigInteger);
+WebIDL::ExceptionOr<ByteBuffer> base64_url_bytes_decode(JS::Realm&, Utf16String const& base64_url_string);
+WebIDL::ExceptionOr<::Crypto::UnsignedBigInteger> base64_url_uint_decode(JS::Realm&, Utf16String const& base64_url_string);
 
 }
diff --git a/Libraries/LibWeb/Crypto/CryptoBindings.cpp b/Libraries/LibWeb/Crypto/CryptoBindings.cpp
index cc4ae6205b..4462686d4e 100644
--- a/Libraries/LibWeb/Crypto/CryptoBindings.cpp
+++ b/Libraries/LibWeb/Crypto/CryptoBindings.cpp
@@ -17,7 +17,7 @@ namespace Web::Crypto {
 
 #define JWK_PARSE_STRING_PROPERTY(name)                                      \
     if (auto value = json_object.get_string(#name##sv); value.has_value()) { \
-        key.name = value.release_value();                                    \
+        key.name = Utf16String::from_utf8(value.release_value());            \
     }
 
 JS::ThrowCompletionOr<JsonWebKey> JsonWebKey::parse(JS::Realm& realm, ReadonlyBytes data)
@@ -66,11 +66,11 @@ JS::ThrowCompletionOr<JsonWebKey> JsonWebKey::parse(JS::Realm& realm, ReadonlyBy
     key.ext = json_object.get_bool("ext"sv);
 
     if (auto key_ops = json_object.get_array("key_ops"sv); key_ops.has_value()) {
-        key.key_ops = Vector<String> {};
+        key.key_ops = Vector<Utf16String> {};
         key.key_ops->ensure_capacity(key_ops->size());
 
         key_ops->for_each([&](auto const& value) {
-            key.key_ops->append(value.as_string());
+            key.key_ops->append(Utf16String::from_utf8(value.as_string()));
         });
     }
 
@@ -91,7 +91,6 @@ JS::ThrowCompletionOr<GC::Ref<JS::Object>> JsonWebKey::to_object(JS::Realm& real
 {
     auto& vm = realm.vm();
     auto object = JS::Object::create(realm, realm.intrinsics().object_prototype());
-
     if (kty.has_value())
         TRY(object->create_data_property("kty"_utf16_fly_string, JS::PrimitiveString::create(vm, kty.value())));
 
@@ -99,8 +98,8 @@ JS::ThrowCompletionOr<GC::Ref<JS::Object>> JsonWebKey::to_object(JS::Realm& real
         TRY(object->create_data_property("use"_utf16_fly_string, JS::PrimitiveString::create(vm, use.value())));
 
     if (key_ops.has_value()) {
-        auto key_ops_array = JS::Array::create_from<String>(realm, key_ops.value().span(), [&](auto& key_usage) -> JS::Value {
-            return JS::PrimitiveString::create(realm.vm(), key_usage);
+        auto key_ops_array = JS::Array::create_from<Utf16String>(realm, key_ops.value().span(), [&](auto& key_usage) -> JS::Value {
+            return JS::PrimitiveString::create(vm, key_usage);
         });
         TRY(object->create_data_property("key_ops"_utf16_fly_string, move(key_ops_array)));
     }
diff --git a/Libraries/LibWeb/Crypto/CryptoBindings.h b/Libraries/LibWeb/Crypto/CryptoBindings.h
index 8134777251..e732abea46 100644
--- a/Libraries/LibWeb/Crypto/CryptoBindings.h
+++ b/Libraries/LibWeb/Crypto/CryptoBindings.h
@@ -9,6 +9,7 @@
 
 #include <AK/Optional.h>
 #include <AK/String.h>
+#include <AK/Utf16String.h>
 #include <AK/Vector.h>
 #include <LibCrypto/BigInt/UnsignedBigInteger.h>
 
@@ -17,36 +18,36 @@ namespace Web::Crypto {
 
 // https://w3c.github.io/webcrypto/#JsonWebKey-dictionary
 struct RsaOtherPrimesInfo {
-    Optional<String> r;
-    Optional<String> d;
-    Optional<String> t;
+    Optional<Utf16String> r;
+    Optional<Utf16String> d;
+    Optional<Utf16String> t;
 };
 
 // https://w3c.github.io/webcrypto/#JsonWebKey-dictionary
 struct JsonWebKey {
-    Optional<String> kty;
-    Optional<String> use;
-    Optional<Vector<String>> key_ops;
-    Optional<String> alg;
+    Optional<Utf16String> kty;
+    Optional<Utf16String> use;
+    Optional<Vector<Utf16String>> key_ops;
+    Optional<Utf16String> alg;
     Optional<bool> ext;
-    Optional<String> crv;
-    Optional<String> x;
-    Optional<String> y;
-    Optional<String> d;
-    Optional<String> n;
-    Optional<String> e;
-    Optional<String> p;
-    Optional<String> q;
-    Optional<String> dp;
-    Optional<String> dq;
-    Optional<String> qi;
+    Optional<Utf16String> crv;
+    Optional<Utf16String> x;
+    Optional<Utf16String> y;
+    Optional<Utf16String> d;
+    Optional<Utf16String> n;
+    Optional<Utf16String> e;
+    Optional<Utf16String> p;
+    Optional<Utf16String> q;
+    Optional<Utf16String> dp;
+    Optional<Utf16String> dq;
+    Optional<Utf16String> qi;
     Optional<Vector<RsaOtherPrimesInfo>> oth;
-    Optional<String> k;
+    Optional<Utf16String> k;
 
     // https://wicg.github.io/webcrypto-modern-algos/#partial-JsonWebKey-dictionary
     // The following fields are defined in draft-ietf-cose-dilithium-07
-    Optional<String> pub;
-    Optional<String> priv;
+    Optional<Utf16String> pub;
+    Optional<Utf16String> priv;
 
     JS::ThrowCompletionOr<GC::Ref<JS::Object>> to_object(JS::Realm&);
 
diff --git a/Libraries/LibWeb/Crypto/CryptoKey.cpp b/Libraries/LibWeb/Crypto/CryptoKey.cpp
index 753d1f646e..57d2724a6d 100644
--- a/Libraries/LibWeb/Crypto/CryptoKey.cpp
+++ b/Libraries/LibWeb/Crypto/CryptoKey.cpp
@@ -131,7 +131,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::Object>> deserialize_key_algorithm(HTML::Transfe
     case KeyAlgorithmTag::EcKeyAlgorithm: {
         auto algorithm = EcKeyAlgorithm::create(realm);
         algorithm->set_name(decoder.decode<String>());
-        algorithm->set_named_curve(decoder.decode<String>());
+        algorithm->set_named_curve(decoder.decode<Utf16String>());
         return algorithm;
     }
     case KeyAlgorithmTag::AesKeyAlgorithm: {
@@ -175,9 +175,9 @@ void serialize_handle(HTML::TransferDataEncoder& encoder, RsaOtherPrimesInfo con
 RsaOtherPrimesInfo deserialize_rsa_other_primes_info(HTML::TransferDataDecoder& decoder)
 {
     return RsaOtherPrimesInfo {
-        .r = decoder.decode<Optional<String>>(),
-        .d = decoder.decode<Optional<String>>(),
-        .t = decoder.decode<Optional<String>>(),
+        .r = decoder.decode<Optional<Utf16String>>(),
+        .d = decoder.decode<Optional<Utf16String>>(),
+        .t = decoder.decode<Optional<Utf16String>>(),
     };
 }
 
@@ -214,22 +214,22 @@ void serialize_handle(HTML::TransferDataEncoder& encoder, JsonWebKey const& jwk)
 JsonWebKey deserialize_json_web_key(HTML::TransferDataDecoder& decoder)
 {
     JsonWebKey jwk;
-    jwk.kty = decoder.decode<Optional<String>>();
-    jwk.use = decoder.decode<Optional<String>>();
-    jwk.key_ops = decoder.decode<Optional<Vector<String>>>();
-    jwk.alg = decoder.decode<Optional<String>>();
+    jwk.kty = decoder.decode<Optional<Utf16String>>();
+    jwk.use = decoder.decode<Optional<Utf16String>>();
+    jwk.key_ops = decoder.decode<Optional<Vector<Utf16String>>>();
+    jwk.alg = decoder.decode<Optional<Utf16String>>();
     jwk.ext = decoder.decode<Optional<bool>>();
-    jwk.crv = decoder.decode<Optional<String>>();
-    jwk.x = decoder.decode<Optional<String>>();
-    jwk.y = decoder.decode<Optional<String>>();
-    jwk.d = decoder.decode<Optional<String>>();
-    jwk.n = decoder.decode<Optional<String>>();
-    jwk.e = decoder.decode<Optional<String>>();
-    jwk.p = decoder.decode<Optional<String>>();
-    jwk.q = decoder.decode<Optional<String>>();
-    jwk.dp = decoder.decode<Optional<String>>();
-    jwk.dq = decoder.decode<Optional<String>>();
-    jwk.qi = decoder.decode<Optional<String>>();
+    jwk.crv = decoder.decode<Optional<Utf16String>>();
+    jwk.x = decoder.decode<Optional<Utf16String>>();
+    jwk.y = decoder.decode<Optional<Utf16String>>();
+    jwk.d = decoder.decode<Optional<Utf16String>>();
+    jwk.n = decoder.decode<Optional<Utf16String>>();
+    jwk.e = decoder.decode<Optional<Utf16String>>();
+    jwk.p = decoder.decode<Optional<Utf16String>>();
+    jwk.q = decoder.decode<Optional<Utf16String>>();
+    jwk.dp = decoder.decode<Optional<Utf16String>>();
+    jwk.dq = decoder.decode<Optional<Utf16String>>();
+    jwk.qi = decoder.decode<Optional<Utf16String>>();
     if (decoder.decode<bool>()) {
         auto size = decoder.decode<u64>();
         Vector<RsaOtherPrimesInfo> oth;
@@ -238,9 +238,9 @@ JsonWebKey deserialize_json_web_key(HTML::TransferDataDecoder& decoder)
             oth.unchecked_append(deserialize_rsa_other_primes_info(decoder));
         jwk.oth = move(oth);
     }
-    jwk.k = decoder.decode<Optional<String>>();
-    jwk.pub = decoder.decode<Optional<String>>();
-    jwk.priv = decoder.decode<Optional<String>>();
+    jwk.k = decoder.decode<Optional<Utf16String>>();
+    jwk.pub = decoder.decode<Optional<Utf16String>>();
+    jwk.priv = decoder.decode<Optional<Utf16String>>();
     return jwk;
 }
 
@@ -443,7 +443,7 @@ void CryptoKey::set_usages(Vector<Bindings::KeyUsage> usages)
     });
 }
 
-String CryptoKey::algorithm_name() const
+String const& CryptoKey::algorithm_name() const
 {
     if (m_algorithm_name.is_empty()) {
         auto name = MUST(m_algorithm_cached->get("name"_utf16_fly_string));
diff --git a/Libraries/LibWeb/Crypto/CryptoKey.h b/Libraries/LibWeb/Crypto/CryptoKey.h
index 21c6b78038..556e6712eb 100644
--- a/Libraries/LibWeb/Crypto/CryptoKey.h
+++ b/Libraries/LibWeb/Crypto/CryptoKey.h
@@ -47,7 +47,7 @@ public:
     void set_usages(Vector<Bindings::KeyUsage>);
 
     InternalKeyData const& handle() const { return m_key_data; }
-    String algorithm_name() const;
+    String const& algorithm_name() const;
 
     virtual WebIDL::ExceptionOr<void> serialization_steps(HTML::TransferDataEncoder&, bool for_storage, HTML::SerializationMemory&) override;
     virtual WebIDL::ExceptionOr<void> deserialization_steps(HTML::TransferDataDecoder&, HTML::DeserializationMemory&) override;
diff --git a/Libraries/LibWeb/Crypto/KeyAlgorithms.cpp b/Libraries/LibWeb/Crypto/KeyAlgorithms.cpp
index 30b62eb91c..e590c9495f 100644
--- a/Libraries/LibWeb/Crypto/KeyAlgorithms.cpp
+++ b/Libraries/LibWeb/Crypto/KeyAlgorithms.cpp
@@ -59,7 +59,7 @@ JS_DEFINE_NATIVE_FUNCTION(KeyAlgorithm::name_getter)
 {
     auto* impl = TRY(impl_from<KeyAlgorithm>(vm, "KeyAlgorithm"sv));
     auto name = TRY(Bindings::throw_dom_exception_if_needed(vm, [&] { return impl->name(); }));
-    return JS::PrimitiveString::create(vm, name);
+    return JS::PrimitiveString::create(vm, Utf16String::from_utf8(name));
 }
 
 void KeyAlgorithm::visit_edges(Visitor& visitor)
diff --git a/Libraries/LibWeb/Crypto/SubtleCrypto.cpp b/Libraries/LibWeb/Crypto/SubtleCrypto.cpp
index 6e19b8a0b9..fdafaee6a0 100644
--- a/Libraries/LibWeb/Crypto/SubtleCrypto.cpp
+++ b/Libraries/LibWeb/Crypto/SubtleCrypto.cpp
@@ -34,38 +34,49 @@ static void normalize_key_usages(Vector<Bindings::KeyUsage>& key_usages)
 
 static JsonWebKey to_internal_json_web_key(Bindings::JsonWebKey bindings_jwk)
 {
+    auto to_utf16 = [](Optional<String> value) -> Optional<Utf16String> {
+        if (!value.has_value())
+            return {};
+        return Utf16String::from_utf8(value.release_value());
+    };
+    auto to_utf16_vector = [](Optional<Vector<String>> values) -> Optional<Vector<Utf16String>> {
+        if (!values.has_value())
+            return {};
+        Vector<Utf16String> result;
+        result.ensure_capacity(values->size());
+        for (auto& value : *values)
+            result.unchecked_append(Utf16String::from_utf8(value));
+        return result;
+    };
+
     JsonWebKey jwk;
-    jwk.alg = move(bindings_jwk.alg);
-    jwk.crv = move(bindings_jwk.crv);
-    jwk.d = move(bindings_jwk.d);
-    jwk.dp = move(bindings_jwk.dp);
-    jwk.dq = move(bindings_jwk.dq);
-    jwk.e = move(bindings_jwk.e);
+    jwk.alg = to_utf16(move(bindings_jwk.alg));
+    jwk.crv = to_utf16(move(bindings_jwk.crv));
+    jwk.d = to_utf16(move(bindings_jwk.d));
+    jwk.dp = to_utf16(move(bindings_jwk.dp));
+    jwk.dq = to_utf16(move(bindings_jwk.dq));
+    jwk.e = to_utf16(move(bindings_jwk.e));
     jwk.ext = move(bindings_jwk.ext);
-    jwk.k = move(bindings_jwk.k);
-    jwk.key_ops = move(bindings_jwk.key_ops);
-    jwk.kty = move(bindings_jwk.kty);
-    jwk.n = move(bindings_jwk.n);
+    jwk.k = to_utf16(move(bindings_jwk.k));
+    jwk.key_ops = to_utf16_vector(move(bindings_jwk.key_ops));
+    jwk.kty = to_utf16(move(bindings_jwk.kty));
+    jwk.n = to_utf16(move(bindings_jwk.n));
     if (bindings_jwk.oth.has_value()) {
         Vector<RsaOtherPrimesInfo> oth;
         oth.ensure_capacity(bindings_jwk.oth->size());
         for (auto& bindings_prime : *bindings_jwk.oth) {
-            oth.append({
-                .r = move(bindings_prime.r),
-                .d = move(bindings_prime.d),
-                .t = move(bindings_prime.t),
-            });
+            oth.append({ .r = to_utf16(move(bindings_prime.r)), .d = to_utf16(move(bindings_prime.d)), .t = to_utf16(move(bindings_prime.t)) });
         }
         jwk.oth = move(oth);
     }
-    jwk.p = move(bindings_jwk.p);
-    jwk.priv = move(bindings_jwk.priv);
-    jwk.pub = move(bindings_jwk.pub);
-    jwk.q = move(bindings_jwk.q);
-    jwk.qi = move(bindings_jwk.qi);
-    jwk.use = move(bindings_jwk.use);
-    jwk.x = move(bindings_jwk.x);
-    jwk.y = move(bindings_jwk.y);
+    jwk.p = to_utf16(move(bindings_jwk.p));
+    jwk.priv = to_utf16(move(bindings_jwk.priv));
+    jwk.pub = to_utf16(move(bindings_jwk.pub));
+    jwk.q = to_utf16(move(bindings_jwk.q));
+    jwk.qi = to_utf16(move(bindings_jwk.qi));
+    jwk.use = to_utf16(move(bindings_jwk.use));
+    jwk.x = to_utf16(move(bindings_jwk.x));
+    jwk.y = to_utf16(move(bindings_jwk.y));
     return jwk;
 }
 
@@ -111,7 +122,7 @@ WebIDL::ExceptionOr<NormalizedAlgorithmAndParameter> normalize_an_algorithm(JS::
         // Return the result of running the normalize an algorithm algorithm,
         // with the alg set to a new Algorithm dictionary whose name attribute is alg, and with the op set to op.
         auto dictionary = JS::Object::create(realm, realm.intrinsics().object_prototype());
-        TRY(dictionary->create_data_property("name"_utf16_fly_string, JS::PrimitiveString::create(vm, algorithm.get<String>())));
+        TRY(dictionary->create_data_property("name"_utf16_fly_string, JS::PrimitiveString::create(vm, Utf16String::from_utf8(algorithm.get<String>()))));
         return normalize_an_algorithm(realm, dictionary, operation);
     }
 
diff --git a/Libraries/LibWeb/DOM/Attr.cpp b/Libraries/LibWeb/DOM/Attr.cpp
index 267e435107..3e795aaf49 100644
--- a/Libraries/LibWeb/DOM/Attr.cpp
+++ b/Libraries/LibWeb/DOM/Attr.cpp
@@ -127,10 +127,10 @@ void Attr::handle_attribute_changes(Element& element, Optional<String> const& ol
         auto& vm = this->vm();
 
         GC::RootVector<JS::Value> arguments;
-        arguments.append(JS::PrimitiveString::create(vm, local_name()));
-        arguments.append(!old_value.has_value() ? JS::js_null() : JS::PrimitiveString::create(vm, old_value.value()));
-        arguments.append(!new_value.has_value() ? JS::js_null() : JS::PrimitiveString::create(vm, new_value.value()));
-        arguments.append(!namespace_uri().has_value() ? JS::js_null() : JS::PrimitiveString::create(vm, namespace_uri().value()));
+        arguments.append(JS::PrimitiveString::create(vm, Utf16FlyString::from_utf8(local_name())));
+        arguments.append(!old_value.has_value() ? JS::js_null() : JS::PrimitiveString::create(vm, Utf16String::from_utf8(old_value.value())));
+        arguments.append(!new_value.has_value() ? JS::js_null() : JS::PrimitiveString::create(vm, Utf16String::from_utf8(new_value.value())));
+        arguments.append(!namespace_uri().has_value() ? JS::js_null() : JS::PrimitiveString::create(vm, Utf16FlyString::from_utf8(namespace_uri().value())));
 
         element.enqueue_a_custom_element_callback_reaction(HTML::CustomElementReactionNames::attributeChangedCallback, move(arguments));
     }
diff --git a/Libraries/LibWeb/DOM/DOMTokenList.cpp b/Libraries/LibWeb/DOM/DOMTokenList.cpp
index 5268d6064d..d838016256 100644
--- a/Libraries/LibWeb/DOM/DOMTokenList.cpp
+++ b/Libraries/LibWeb/DOM/DOMTokenList.cpp
@@ -353,7 +353,7 @@ Optional<JS::Value> DOMTokenList::item_value(size_t index) const
     auto string = item(index);
     if (!string.has_value())
         return {};
-    return JS::PrimitiveString::create(vm(), string.release_value());
+    return JS::PrimitiveString::create(vm(), Utf16String::from_utf8(string.release_value()));
 }
 
 }
diff --git a/Libraries/LibWeb/DOM/Element.cpp b/Libraries/LibWeb/DOM/Element.cpp
index 28003ca407..f3617d519c 100644
--- a/Libraries/LibWeb/DOM/Element.cpp
+++ b/Libraries/LibWeb/DOM/Element.cpp
@@ -3471,10 +3471,10 @@ JS::ThrowCompletionOr<void> Element::upgrade_element(GC::Ref<HTML::CustomElement
 
         GC::RootVector<JS::Value> arguments;
 
-        arguments.append(JS::PrimitiveString::create(vm, attribute->local_name()));
+        arguments.append(JS::PrimitiveString::create(vm, Utf16FlyString::from_utf8(attribute->local_name())));
         arguments.append(JS::js_null());
-        arguments.append(JS::PrimitiveString::create(vm, attribute->value()));
-        arguments.append(attribute->namespace_uri().has_value() ? JS::PrimitiveString::create(vm, attribute->namespace_uri().value()) : JS::js_null());
+        arguments.append(JS::PrimitiveString::create(vm, Utf16String::from_utf8(attribute->value())));
+        arguments.append(attribute->namespace_uri().has_value() ? JS::PrimitiveString::create(vm, Utf16FlyString::from_utf8(attribute->namespace_uri().value())) : JS::js_null());
 
         enqueue_a_custom_element_callback_reaction(HTML::CustomElementReactionNames::attributeChangedCallback, move(arguments));
     }
diff --git a/Libraries/LibWeb/DOM/EventTarget.cpp b/Libraries/LibWeb/DOM/EventTarget.cpp
index 25842c495e..a60f7cf4ba 100644
--- a/Libraries/LibWeb/DOM/EventTarget.cpp
+++ b/Libraries/LibWeb/DOM/EventTarget.cpp
@@ -9,6 +9,7 @@
  */
 
 #include <AK/StringBuilder.h>
+#include <AK/Utf16StringBuilder.h>
 #include <LibJS/Runtime/AbstractOperations.h>
 #include <LibJS/Runtime/ECMAScriptFunctionObject.h>
 #include <LibJS/Runtime/ExternalMemory.h>
@@ -494,7 +495,7 @@ WebIDL::CallbackType* EventTarget::get_current_value_of_event_handler(FlyString
         auto& settings_object = document->relevant_settings_object();
 
         // Build source text and parameter strings for the event handler function.
-        StringBuilder source_builder(StringBuilder::Mode::UTF16);
+        Utf16StringBuilder source_builder;
         Utf16String parameters_string;
 
         // sourceText / ParameterList
@@ -510,7 +511,7 @@ WebIDL::CallbackType* EventTarget::get_current_value_of_event_handler(FlyString
             parameters_string = "event"_utf16;
         }
 
-        auto source_text = source_builder.to_utf16_string();
+        auto source_text = source_builder.to_string();
 
         auto& vm = Bindings::main_thread_vm();
 
diff --git a/Libraries/LibWeb/DOMURL/URLSearchParamsIterator.cpp b/Libraries/LibWeb/DOMURL/URLSearchParamsIterator.cpp
index 0db99c20c5..f933ee573e 100644
--- a/Libraries/LibWeb/DOMURL/URLSearchParamsIterator.cpp
+++ b/Libraries/LibWeb/DOMURL/URLSearchParamsIterator.cpp
@@ -58,11 +58,11 @@ JS::Object* URLSearchParamsIterator::next()
 
     auto& entry = m_url_search_params->m_list[m_index++];
     if (m_iteration_kind == JS::Object::PropertyKind::Key)
-        return create_iterator_result_object(vm(), JS::PrimitiveString::create(vm(), entry.name), false);
+        return create_iterator_result_object(vm(), JS::PrimitiveString::create(vm(), Utf16String::from_utf8(entry.name)), false);
     else if (m_iteration_kind == JS::Object::PropertyKind::Value)
-        return create_iterator_result_object(vm(), JS::PrimitiveString::create(vm(), entry.value), false);
+        return create_iterator_result_object(vm(), JS::PrimitiveString::create(vm(), Utf16String::from_utf8(entry.value)), false);
 
-    return create_iterator_result_object(vm(), JS::Array::create_from(realm(), { JS::PrimitiveString::create(vm(), entry.name), JS::PrimitiveString::create(vm(), entry.value) }), false);
+    return create_iterator_result_object(vm(), JS::Array::create_from(realm(), { JS::PrimitiveString::create(vm(), Utf16String::from_utf8(entry.name)), JS::PrimitiveString::create(vm(), Utf16String::from_utf8(entry.value)) }), false);
 }
 
 }
diff --git a/Libraries/LibWeb/Encoding/TextDecoderStream.cpp b/Libraries/LibWeb/Encoding/TextDecoderStream.cpp
index 2267824cea..d69d261279 100644
--- a/Libraries/LibWeb/Encoding/TextDecoderStream.cpp
+++ b/Libraries/LibWeb/Encoding/TextDecoderStream.cpp
@@ -155,7 +155,7 @@ WebIDL::ExceptionOr<void> TextDecoderStream::enqueue_decoded_output(String const
     if (fatal() && decoded.contains(0xFFFD))
         return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, "Decoding failed"sv };
 
-    auto js_string = JS::PrimitiveString::create(vm, decoded);
+    auto js_string = JS::PrimitiveString::create(vm, Utf16String::from_utf8(decoded));
     return Streams::transform_stream_default_controller_enqueue(*m_transform->controller(), js_string);
 }
 
diff --git a/Libraries/LibWeb/Fetch/Body.cpp b/Libraries/LibWeb/Fetch/Body.cpp
index b84be1e855..5e7f27f431 100644
--- a/Libraries/LibWeb/Fetch/Body.cpp
+++ b/Libraries/LibWeb/Fetch/Body.cpp
@@ -173,7 +173,7 @@ WebIDL::ExceptionOr<GC::Ref<WebIDL::Promise>> BodyMixin::text() const
         VERIFY(decoder.has_value());
 
         auto utf8_text = MUST(TextCodec::convert_input_to_utf8_using_given_decoder_unless_there_is_a_byte_order_mark(*decoder, bytes));
-        return JS::PrimitiveString::create(vm, move(utf8_text));
+        return JS::PrimitiveString::create(vm, Utf16String::from_utf8(utf8_text));
     }));
 }
 
diff --git a/Libraries/LibWeb/Fetch/HeadersIterator.cpp b/Libraries/LibWeb/Fetch/HeadersIterator.cpp
index f4127965df..7b3b2c1862 100644
--- a/Libraries/LibWeb/Fetch/HeadersIterator.cpp
+++ b/Libraries/LibWeb/Fetch/HeadersIterator.cpp
@@ -71,11 +71,11 @@ GC::Ref<JS::Object> HeadersIterator::next()
 
     switch (m_iteration_kind) {
     case JS::Object::PropertyKind::Key:
-        return create_iterator_result_object(vm(), JS::PrimitiveString::create(vm(), pair_name), false);
+        return create_iterator_result_object(vm(), JS::PrimitiveString::create(vm(), Utf16String::from_utf8(pair_name)), false);
     case JS::Object::PropertyKind::Value:
-        return create_iterator_result_object(vm(), JS::PrimitiveString::create(vm(), pair_value), false);
+        return create_iterator_result_object(vm(), JS::PrimitiveString::create(vm(), Utf16String::from_utf8(pair_value)), false);
     case JS::Object::PropertyKind::KeyAndValue: {
-        auto array = JS::Array::create_from(realm(), { JS::PrimitiveString::create(vm(), pair_name), JS::PrimitiveString::create(vm(), pair_value) });
+        auto array = JS::Array::create_from(realm(), { JS::PrimitiveString::create(vm(), Utf16String::from_utf8(pair_name)), JS::PrimitiveString::create(vm(), Utf16String::from_utf8(pair_value)) });
         return create_iterator_result_object(vm(), array, false);
     }
     default:
diff --git a/Libraries/LibWeb/FileAPI/Blob.cpp b/Libraries/LibWeb/FileAPI/Blob.cpp
index aa784b1e8d..c700684780 100644
--- a/Libraries/LibWeb/FileAPI/Blob.cpp
+++ b/Libraries/LibWeb/FileAPI/Blob.cpp
@@ -399,7 +399,7 @@ GC::Ref<WebIDL::Promise> Blob::text()
 
         auto decoder = TextCodec::decoder_for("UTF-8"sv);
         auto utf8_text = TRY_OR_THROW_OOM(vm, TextCodec::convert_input_to_utf8_using_given_decoder_unless_there_is_a_byte_order_mark(*decoder, array_buffer.bytes()));
-        return JS::PrimitiveString::create(vm, move(utf8_text));
+        return JS::PrimitiveString::create(vm, Utf16String::from_utf8(utf8_text));
     }));
 }
 
diff --git a/Libraries/LibWeb/Geometry/DOMMatrixReadOnly.cpp b/Libraries/LibWeb/Geometry/DOMMatrixReadOnly.cpp
index 6b6d054cda..7621715550 100644
--- a/Libraries/LibWeb/Geometry/DOMMatrixReadOnly.cpp
+++ b/Libraries/LibWeb/Geometry/DOMMatrixReadOnly.cpp
@@ -567,37 +567,37 @@ WebIDL::ExceptionOr<String> DOMMatrixReadOnly::to_string() const
         TRY_OR_THROW_OOM(vm, builder.try_append("matrix("sv));
 
         // 2. Append ! ToString(m11 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m11())));
+        JS::number_to_string(builder, m11());
 
         // 3. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 4. Append ! ToString(m12 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m12())));
+        JS::number_to_string(builder, m12());
 
         // 5. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 6. Append ! ToString(m21 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m21())));
+        JS::number_to_string(builder, m21());
 
         // 7. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 8. Append ! ToString(m22 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m22())));
+        JS::number_to_string(builder, m22());
 
         // 9. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 10. Append ! ToString(m41 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m41())));
+        JS::number_to_string(builder, m41());
 
         // 11. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 12. Append ! ToString(m42 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m42())));
+        JS::number_to_string(builder, m42());
 
         // 13. Append ")" to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(")"sv));
@@ -606,83 +606,83 @@ WebIDL::ExceptionOr<String> DOMMatrixReadOnly::to_string() const
         TRY_OR_THROW_OOM(vm, builder.try_append("matrix3d("sv));
 
         // 2. Append ! ToString(m11 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m11())));
+        JS::number_to_string(builder, m11());
 
         // 3. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 4. Append ! ToString(m12 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m12())));
+        JS::number_to_string(builder, m12());
 
         // 5. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 6. Append ! ToString(m13 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m13())));
+        JS::number_to_string(builder, m13());
 
         // 7. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 8. Append ! ToString(m14 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m14())));
+        JS::number_to_string(builder, m14());
 
         // 9. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 10. Append ! ToString(m21 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m21())));
+        JS::number_to_string(builder, m21());
 
         // 11. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 12. Append ! ToString(m22 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m22())));
+        JS::number_to_string(builder, m22());
 
         // 13. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 14. Append ! ToString(m23 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m23())));
+        JS::number_to_string(builder, m23());
 
         // 15. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 16. Append ! ToString(m24 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m24())));
+        JS::number_to_string(builder, m24());
 
         // 17. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // NOTE: The spec doesn't include the steps to append m31 to m34, but they are required as matrix3d requires 16 elements.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m31())));
+        JS::number_to_string(builder, m31());
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m32())));
+        JS::number_to_string(builder, m32());
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m33())));
+        JS::number_to_string(builder, m33());
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m34())));
+        JS::number_to_string(builder, m34());
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 18. Append ! ToString(m41 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m41())));
+        JS::number_to_string(builder, m41());
 
         // 19. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 20. Append ! ToString(m42 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m42())));
+        JS::number_to_string(builder, m42());
 
         // 21. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 22. Append ! ToString(m43 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m43())));
+        JS::number_to_string(builder, m43());
 
         // 23. Append ", " to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(", "sv));
 
         // 24. Append ! ToString(m44 element) to string.
-        TRY_OR_THROW_OOM(vm, builder.try_append(JS::number_to_string(m44())));
+        JS::number_to_string(builder, m44());
 
         // 25. Append ")" to string.
         TRY_OR_THROW_OOM(vm, builder.try_append(")"sv));
diff --git a/Libraries/LibWeb/HTML/CrossOrigin/AbstractOperations.cpp b/Libraries/LibWeb/HTML/CrossOrigin/AbstractOperations.cpp
index a9e51d20c9..9546846714 100644
--- a/Libraries/LibWeb/HTML/CrossOrigin/AbstractOperations.cpp
+++ b/Libraries/LibWeb/HTML/CrossOrigin/AbstractOperations.cpp
@@ -484,7 +484,7 @@ GC::RootVector<JS::Value> cross_origin_own_property_keys(Variant<HTML::Location
 
     // 2. For each e of CrossOriginProperties(O), append e.[[Property]] to keys.
     for (auto& entry : cross_origin_properties(object))
-        keys.append(JS::PrimitiveString::create(vm, move(entry.property)));
+        keys.append(JS::PrimitiveString::create(vm, Utf16String::from_utf8(entry.property)));
 
     // 3. Return the concatenation of keys and « "then", @@toStringTag, @@hasInstance, @@isConcatSpreadable ».
     keys.append(JS::PrimitiveString::create(vm, vm.names.then.as_string()));
diff --git a/Libraries/LibWeb/HTML/CustomElements/CustomStateSet.cpp b/Libraries/LibWeb/HTML/CustomElements/CustomStateSet.cpp
index 65e03fe31e..7fb9474372 100644
--- a/Libraries/LibWeb/HTML/CustomElements/CustomStateSet.cpp
+++ b/Libraries/LibWeb/HTML/CustomElements/CustomStateSet.cpp
@@ -43,7 +43,7 @@ void CustomStateSet::visit_edges(Cell::Visitor& visitor)
 
 bool CustomStateSet::has_state(FlyString const& state) const
 {
-    return m_set_entries->set_has(JS::PrimitiveString::create(realm().vm(), state));
+    return m_set_entries->set_has(JS::PrimitiveString::create(realm().vm(), Utf16FlyString::from_utf8(state)));
 }
 
 void CustomStateSet::on_set_modified_from_js(Badge<Bindings::CustomStateSetPrototype>)
diff --git a/Libraries/LibWeb/HTML/DOMParser.cpp b/Libraries/LibWeb/HTML/DOMParser.cpp
index ec2b821bb5..0af9b3c01c 100644
--- a/Libraries/LibWeb/HTML/DOMParser.cpp
+++ b/Libraries/LibWeb/HTML/DOMParser.cpp
@@ -59,7 +59,7 @@ WebIDL::ExceptionOr<GC::Ref<DOM::Document>> DOMParser::parse_from_string(Trusted
     if (type == Bindings::DOMParserSupportedType::Text_Html) {
         // -> "text/html"
         document = HTML::HTMLDocument::create(realm(), associated_document.url());
-        document->set_content_type(Bindings::idl_enum_to_string(type));
+        document->set_content_type("text/html"_string);
         document->set_document_type(DOM::Document::Type::HTML);
 
         // 1. Parse HTML from a string given document and compliantString.
@@ -67,7 +67,22 @@ WebIDL::ExceptionOr<GC::Ref<DOM::Document>> DOMParser::parse_from_string(Trusted
     } else {
         // -> Otherwise
         document = DOM::Document::create(realm(), associated_document.url());
-        document->set_content_type(Bindings::idl_enum_to_string(type));
+        switch (type) {
+        case Bindings::DOMParserSupportedType::Text_Xml:
+            document->set_content_type("text/xml"_string);
+            break;
+        case Bindings::DOMParserSupportedType::Application_Xml:
+            document->set_content_type("application/xml"_string);
+            break;
+        case Bindings::DOMParserSupportedType::Application_XhtmlXml:
+            document->set_content_type("application/xhtml+xml"_string);
+            break;
+        case Bindings::DOMParserSupportedType::Image_SvgXml:
+            document->set_content_type("image/svg+xml"_string);
+            break;
+        case Bindings::DOMParserSupportedType::Text_Html:
+            VERIFY_NOT_REACHED();
+        }
         document->set_document_type(DOM::Document::Type::XML);
 
         // 1. Create an XML parser parse, associated with document, and with XML scripting support disabled.
diff --git a/Libraries/LibWeb/HTML/DOMStringList.cpp b/Libraries/LibWeb/HTML/DOMStringList.cpp
index 819431393a..1ab4dc1de1 100644
--- a/Libraries/LibWeb/HTML/DOMStringList.cpp
+++ b/Libraries/LibWeb/HTML/DOMStringList.cpp
@@ -61,7 +61,7 @@ Optional<JS::Value> DOMStringList::item_value(size_t index) const
     if (index >= m_list.size())
         return {};
 
-    return JS::PrimitiveString::create(vm(), m_list.at(index));
+    return JS::PrimitiveString::create(vm(), Utf16String::from_utf8(m_list.at(index)));
 }
 
 }
diff --git a/Libraries/LibWeb/HTML/DOMStringMap.cpp b/Libraries/LibWeb/HTML/DOMStringMap.cpp
index 0dfb4df69b..5657988b50 100644
--- a/Libraries/LibWeb/HTML/DOMStringMap.cpp
+++ b/Libraries/LibWeb/HTML/DOMStringMap.cpp
@@ -208,7 +208,7 @@ WebIDL::ExceptionOr<Bindings::PlatformObject::DidDeletionFail> DOMStringMap::del
 
 JS::Value DOMStringMap::named_item_value(FlyString const& name) const
 {
-    return JS::PrimitiveString::create(vm(), determine_value_of_named_property(name));
+    return JS::PrimitiveString::create(vm(), Utf16String::from_utf8(determine_value_of_named_property(name)));
 }
 
 }
diff --git a/Libraries/LibWeb/HTML/DataTransferItem.cpp b/Libraries/LibWeb/HTML/DataTransferItem.cpp
index 066379e517..e2e0b8d984 100644
--- a/Libraries/LibWeb/HTML/DataTransferItem.cpp
+++ b/Libraries/LibWeb/HTML/DataTransferItem.cpp
@@ -113,7 +113,7 @@ void DataTransferItem::get_as_string(GC::Ptr<WebIDL::CallbackType> callback) con
 
     // 4. Otherwise, queue a task to invoke callback, passing the actual data of the item represented by the
     //    DataTransferItem object as the argument.
-    auto data = JS::PrimitiveString::create(vm, MUST(String::from_utf8({ item.data })));
+    auto data = JS::PrimitiveString::create(vm, Utf16String::from_utf8({ item.data }));
 
     HTML::queue_a_task(HTML::Task::Source::Unspecified, nullptr, nullptr,
         GC::Function<void()>::create(realm.heap(), [callback, data]() {
diff --git a/Libraries/LibWeb/HTML/ErrorEvent.cpp b/Libraries/LibWeb/HTML/ErrorEvent.cpp
index 04ac323561..115b0736bd 100644
--- a/Libraries/LibWeb/HTML/ErrorEvent.cpp
+++ b/Libraries/LibWeb/HTML/ErrorEvent.cpp
@@ -26,8 +26,8 @@ WebIDL::ExceptionOr<GC::Ref<ErrorEvent>> ErrorEvent::construct_impl(JS::Realm& r
 
 ErrorEvent::ErrorEvent(JS::Realm& realm, FlyString const& event_name, Bindings::ErrorEventInit const& event_init)
     : DOM::Event(realm, event_name, event_init)
-    , m_message(event_init.message)
-    , m_filename(event_init.filename)
+    , m_message(Utf16String::from_utf8(event_init.message))
+    , m_filename(Utf16String::from_utf8(event_init.filename))
     , m_lineno(event_init.lineno)
     , m_colno(event_init.colno)
     , m_error(event_init.error.value_or(JS::js_undefined()))
diff --git a/Libraries/LibWeb/HTML/ErrorEvent.h b/Libraries/LibWeb/HTML/ErrorEvent.h
index 99f15b9275..79049c3eb8 100644
--- a/Libraries/LibWeb/HTML/ErrorEvent.h
+++ b/Libraries/LibWeb/HTML/ErrorEvent.h
@@ -24,10 +24,10 @@ public:
     virtual ~ErrorEvent() override;
 
     // https://html.spec.whatwg.org/multipage/webappapis.html#dom-errorevent-message
-    String const& message() const { return m_message; }
+    Utf16String const& message() const { return m_message; }
 
     // https://html.spec.whatwg.org/multipage/webappapis.html#dom-errorevent-filename
-    String const& filename() const { return m_filename; }
+    Utf16String const& filename() const { return m_filename; }
 
     // https://html.spec.whatwg.org/multipage/webappapis.html#dom-errorevent-lineno
     u32 lineno() const { return m_lineno; }
@@ -44,8 +44,8 @@ private:
     virtual void initialize(JS::Realm&) override;
     virtual void visit_edges(Cell::Visitor&) override;
 
-    String m_message;
-    String m_filename; // FIXME: This should be a USVString.
+    Utf16String m_message;
+    Utf16String m_filename;
     u32 m_lineno { 0 };
     u32 m_colno { 0 };
     JS::Value m_error;
diff --git a/Libraries/LibWeb/HTML/EventSource.cpp b/Libraries/LibWeb/HTML/EventSource.cpp
index 2aaa2976be..51d93d9f19 100644
--- a/Libraries/LibWeb/HTML/EventSource.cpp
+++ b/Libraries/LibWeb/HTML/EventSource.cpp
@@ -5,6 +5,7 @@
  */
 
 #include <AK/ScopeGuard.h>
+#include <AK/Utf16String.h>
 #include <LibCore/EventLoop.h>
 #include <LibGC/Heap.h>
 #include <LibJS/Runtime/Realm.h>
@@ -445,7 +446,7 @@ void EventSource::dispatch_the_event()
     // 6. If the event type buffer has a value other than the empty string, change the type of the newly created event to equal
     //    the value of the event type buffer.
     Bindings::MessageEventInit init;
-    init.data = JS::PrimitiveString::create(vm(), data_buffer);
+    init.data = JS::PrimitiveString::create(vm(), Utf16String::from_utf8(data_buffer));
     init.last_event_id = last_event_id;
 
     auto type = m_event_type.is_empty() ? HTML::EventNames::message : m_event_type;
diff --git a/Libraries/LibWeb/HTML/NavigateEvent.h b/Libraries/LibWeb/HTML/NavigateEvent.h
index 3c4f557813..8f27e8c791 100644
--- a/Libraries/LibWeb/HTML/NavigateEvent.h
+++ b/Libraries/LibWeb/HTML/NavigateEvent.h
@@ -135,18 +135,18 @@ private:
 namespace AK {
 
 template<>
-struct Formatter<Web::Bindings::NavigationScrollBehavior> : Formatter<StringView> {
+struct Formatter<Web::Bindings::NavigationScrollBehavior> : Formatter<Utf16String> {
     ErrorOr<void> format(FormatBuilder& builder, Web::Bindings::NavigationScrollBehavior const& value)
     {
-        return Formatter<StringView>::format(builder, Web::Bindings::idl_enum_to_string(value));
+        return Formatter<Utf16String>::format(builder, Web::Bindings::idl_enum_to_string(value));
     }
 };
 
 template<>
-struct Formatter<Web::Bindings::NavigationFocusReset> : Formatter<StringView> {
+struct Formatter<Web::Bindings::NavigationFocusReset> : Formatter<Utf16String> {
     ErrorOr<void> format(FormatBuilder& builder, Web::Bindings::NavigationFocusReset const& value)
     {
-        return Formatter<StringView>::format(builder, Web::Bindings::idl_enum_to_string(value));
+        return Formatter<Utf16String>::format(builder, Web::Bindings::idl_enum_to_string(value));
     }
 };
 
diff --git a/Libraries/LibWeb/HTML/Scripting/ClassicScript.cpp b/Libraries/LibWeb/HTML/Scripting/ClassicScript.cpp
index d17b539899..1efae5ece4 100644
--- a/Libraries/LibWeb/HTML/Scripting/ClassicScript.cpp
+++ b/Libraries/LibWeb/HTML/Scripting/ClassicScript.cpp
@@ -56,10 +56,10 @@ GC::Ref<ClassicScript> ClassicScript::create(ByteString filename, StringView sou
     // 11. If result is a list of errors, then:
     if (result.is_error()) {
         auto& parse_error = result.error().first();
-        dbgln_if(HTML_SCRIPT_DEBUG, "ClassicScript: Failed to parse: {}", parse_error.to_string());
+        dbgln_if(HTML_SCRIPT_DEBUG, "ClassicScript: Failed to parse: {}", parse_error.to_utf16_string());
 
         // 1. Set script's parse error and its error to rethrow to result[0].
-        script->set_parse_error(JS::SyntaxError::create(settings.realm(), parse_error.to_string()));
+        script->set_parse_error(JS::SyntaxError::create(settings.realm(), parse_error.to_utf16_string()));
         script->set_error_to_rethrow(script->parse_error());
 
         // 2. Return script.
@@ -93,9 +93,9 @@ GC::Ref<ClassicScript> ClassicScript::create_from_pre_parsed(ByteString filename
 
     if (result.is_error()) {
         auto& parse_error = result.error().first();
-        dbgln_if(HTML_SCRIPT_DEBUG, "ClassicScript: Failed to compile: {}", parse_error.to_string());
+        dbgln_if(HTML_SCRIPT_DEBUG, "ClassicScript: Failed to compile: {}", parse_error.to_utf16_string());
 
-        script->set_parse_error(JS::SyntaxError::create(realm, parse_error.to_string()));
+        script->set_parse_error(JS::SyntaxError::create(realm, parse_error.to_utf16_string()));
         script->set_error_to_rethrow(script->parse_error());
 
         return script;
@@ -126,9 +126,9 @@ GC::Ref<ClassicScript> ClassicScript::create_from_pre_compiled(ByteString filena
 
     if (result.is_error()) {
         auto& parse_error = result.error().first();
-        dbgln_if(HTML_SCRIPT_DEBUG, "ClassicScript: Failed to materialize: {}", parse_error.to_string());
+        dbgln_if(HTML_SCRIPT_DEBUG, "ClassicScript: Failed to materialize: {}", parse_error.to_utf16_string());
 
-        script->set_parse_error(JS::SyntaxError::create(realm, parse_error.to_string()));
+        script->set_parse_error(JS::SyntaxError::create(realm, parse_error.to_utf16_string()));
         script->set_error_to_rethrow(script->parse_error());
 
         return script;
@@ -159,9 +159,9 @@ GC::Ref<ClassicScript> ClassicScript::create_from_bytecode_cache(ByteString file
 
     if (result.is_error()) {
         auto& parse_error = result.error().first();
-        dbgln_if(HTML_SCRIPT_DEBUG, "ClassicScript: Failed to materialize bytecode cache: {}", parse_error.to_string());
+        dbgln_if(HTML_SCRIPT_DEBUG, "ClassicScript: Failed to materialize bytecode cache: {}", parse_error.to_utf16_string());
 
-        script->set_parse_error(JS::SyntaxError::create(realm, parse_error.to_string()));
+        script->set_parse_error(JS::SyntaxError::create(realm, parse_error.to_utf16_string()));
         script->set_error_to_rethrow(script->parse_error());
 
         return script;
diff --git a/Libraries/LibWeb/HTML/Scripting/ModuleScript.cpp b/Libraries/LibWeb/HTML/Scripting/ModuleScript.cpp
index 682457c09b..0d99324aad 100644
--- a/Libraries/LibWeb/HTML/Scripting/ModuleScript.cpp
+++ b/Libraries/LibWeb/HTML/Scripting/ModuleScript.cpp
@@ -54,10 +54,10 @@ WebIDL::ExceptionOr<GC::Ptr<ModuleScript>> ModuleScript::create_a_javascript_mod
     // 8. If result is a list of errors, then:
     if (result.is_error()) {
         auto& parse_error = result.error().first();
-        dbgln("JavaScriptModuleScript: Failed to parse: {}", parse_error.to_string());
+        dbgln("JavaScriptModuleScript: Failed to parse: {}", parse_error.to_utf16_string());
 
         // 1. Set script's parse error to result[0].
-        script->set_parse_error(JS::SyntaxError::create(realm, parse_error.to_string()));
+        script->set_parse_error(JS::SyntaxError::create(realm, parse_error.to_utf16_string()));
 
         // 2. Return script.
         return script;
@@ -82,8 +82,8 @@ WebIDL::ExceptionOr<GC::Ptr<ModuleScript>> ModuleScript::create_from_pre_parsed(
 
     if (result.is_error()) {
         auto& parse_error = result.error().first();
-        dbgln("JavaScriptModuleScript: Failed to parse: {}", parse_error.to_string());
-        script->set_parse_error(JS::SyntaxError::create(realm, parse_error.to_string()));
+        dbgln("JavaScriptModuleScript: Failed to parse: {}", parse_error.to_utf16_string());
+        script->set_parse_error(JS::SyntaxError::create(realm, parse_error.to_utf16_string()));
         return script;
     }
 
@@ -103,8 +103,8 @@ WebIDL::ExceptionOr<GC::Ptr<ModuleScript>> ModuleScript::create_from_pre_compile
 
     if (result.is_error()) {
         auto& parse_error = result.error().first();
-        dbgln("JavaScriptModuleScript: Failed to materialize: {}", parse_error.to_string());
-        script->set_parse_error(JS::SyntaxError::create(realm, parse_error.to_string()));
+        dbgln("JavaScriptModuleScript: Failed to materialize: {}", parse_error.to_utf16_string());
+        script->set_parse_error(JS::SyntaxError::create(realm, parse_error.to_utf16_string()));
         return script;
     }
 
@@ -124,8 +124,8 @@ WebIDL::ExceptionOr<GC::Ptr<ModuleScript>> ModuleScript::create_from_bytecode_ca
 
     if (result.is_error()) {
         auto& parse_error = result.error().first();
-        dbgln("JavaScriptModuleScript: Failed to materialize bytecode cache: {}", parse_error.to_string());
-        script->set_parse_error(JS::SyntaxError::create(realm, parse_error.to_string()));
+        dbgln("JavaScriptModuleScript: Failed to materialize bytecode cache: {}", parse_error.to_utf16_string());
+        script->set_parse_error(JS::SyntaxError::create(realm, parse_error.to_utf16_string()));
         return script;
     }
 
diff --git a/Libraries/LibWeb/HTML/Storage.cpp b/Libraries/LibWeb/HTML/Storage.cpp
index 0be5ac09c5..9dd96f0fea 100644
--- a/Libraries/LibWeb/HTML/Storage.cpp
+++ b/Libraries/LibWeb/HTML/Storage.cpp
@@ -281,7 +281,7 @@ JS::Value Storage::named_item_value(FlyString const& name) const
         // AD-HOC: Spec leaves open to a description at: https://html.spec.whatwg.org/multipage/webstorage.html#the-storage-interface
         // However correct behavior expected here: https://github.com/whatwg/html/issues/8684
         return JS::js_undefined();
-    return JS::PrimitiveString::create(vm(), value.release_value());
+    return JS::PrimitiveString::create(vm(), Utf16String::from_utf8(value.release_value()));
 }
 
 WebIDL::ExceptionOr<Bindings::PlatformObject::DidDeletionFail> Storage::delete_value(String const& name)
diff --git a/Libraries/LibWeb/HTML/StructuredSerialize.cpp b/Libraries/LibWeb/HTML/StructuredSerialize.cpp
index 6538f5396e..557e0088c0 100644
--- a/Libraries/LibWeb/HTML/StructuredSerialize.cpp
+++ b/Libraries/LibWeb/HTML/StructuredSerialize.cpp
@@ -302,7 +302,7 @@ public:
             serialized.encode(MUST(value.as_bigint().big_integer().to_base(10)));
         } else if (value.is_string()) {
             serialized.encode(ValueTag::StringPrimitive);
-            serialized.encode(value.as_string().utf16_string_view().to_utf8_but_should_be_ported_to_utf16());
+            serialized.encode(value.as_string().utf16_string());
         } else {
             return_primitive_type = false;
         }
@@ -338,7 +338,7 @@ public:
             // 10. Otherwise, if value has a [[StringData]] internal slot, then set serialized to { [[Type]]: "String", [[StringData]]: value.[[StringData]] }.
             else if (auto const* string_object = as_if<JS::StringObject>(*object)) {
                 serialized.encode(ValueTag::StringObject);
-                serialized.encode(string_object->primitive_string().utf16_string_view().to_utf8_but_should_be_ported_to_utf16());
+                serialized.encode(string_object->primitive_string().utf16_string());
             }
 
             // 11. Otherwise, if value has a [[DateValue]] internal slot, then set serialized to { [[Type]]: "Date", [[DateValue]]: value.[[DateValue]] }.
@@ -619,7 +619,7 @@ public:
         auto is_primitive = false;
 
         auto decode_string = [&]() {
-            auto string = m_serialized.decode<String>();
+            auto string = m_serialized.decode<Utf16String>();
             return JS::PrimitiveString::create(m_vm, string);
         };
 
diff --git a/Libraries/LibWeb/HTML/WindowOrWorkerGlobalScope.cpp b/Libraries/LibWeb/HTML/WindowOrWorkerGlobalScope.cpp
index da5af9356d..229e8b13cf 100644
--- a/Libraries/LibWeb/HTML/WindowOrWorkerGlobalScope.cpp
+++ b/Libraries/LibWeb/HTML/WindowOrWorkerGlobalScope.cpp
@@ -622,8 +622,8 @@ i32 WindowOrWorkerGlobalScopeMixin::run_timer_initialization_steps(TimerHandler
                 // 2. Assert: handler is a string.
                 // 3. Perform EnsureCSPDoesNotBlockStringCompilation(realm, « », handler, handler, timer, « », handler).
                 //    If this throws an exception, catch it, report it for global, and abort these steps.
-                auto handler_primitive_string = JS::PrimitiveString::create(vm, source);
                 auto source_utf16 = Utf16String::from_utf8(source);
+                auto handler_primitive_string = JS::PrimitiveString::create(vm, source_utf16);
                 if (auto result = ContentSecurityPolicy::ensure_csp_does_not_block_string_compilation(realm, {}, source_utf16, source_utf16, JS::CompilationType::Timer, {}, handler_primitive_string); result.is_throw_completion()) {
                     report_exception(result, realm);
                     return false;
@@ -1194,7 +1194,7 @@ GC::Ref<JS::Object> WindowOrWorkerGlobalScopeMixin::supported_entry_types() cons
         GC::RootVector<JS::Value> supported_entry_types;
 
 #define __ENUMERATE_SUPPORTED_PERFORMANCE_ENTRY_TYPES(entry_type, cpp_class) \
-    supported_entry_types.append(JS::PrimitiveString::create(vm, entry_type));
+    supported_entry_types.append(JS::PrimitiveString::create(vm, Utf16FlyString::from_utf8(entry_type)));
         ENUMERATE_SUPPORTED_PERFORMANCE_ENTRY_TYPES
 #undef __ENUMERATE_SUPPORTED_PERFORMANCE_ENTRY_TYPES
 
diff --git a/Libraries/LibWeb/IndexedDB/IDBFactory.cpp b/Libraries/LibWeb/IndexedDB/IDBFactory.cpp
index 166c4f2bec..65591b93f5 100644
--- a/Libraries/LibWeb/IndexedDB/IDBFactory.cpp
+++ b/Libraries/LibWeb/IndexedDB/IDBFactory.cpp
@@ -218,7 +218,7 @@ GC::Ref<WebIDL::Promise> IDBFactory::databases()
             auto info = JS::Object::create(realm, realm.intrinsics().object_prototype());
 
             // 3. Set info’s name dictionary member to db’s name.
-            MUST(info->create_data_property("name"_utf16_fly_string, JS::PrimitiveString::create(realm.vm(), db->name())));
+            MUST(info->create_data_property("name"_utf16_fly_string, JS::PrimitiveString::create(realm.vm(), Utf16String::from_utf8(db->name()))));
 
             // 4. Set info’s version dictionary member to db’s version.
             MUST(info->create_data_property("version"_utf16_fly_string, JS::Value(db->version())));
diff --git a/Libraries/LibWeb/IndexedDB/IDBIndex.cpp b/Libraries/LibWeb/IndexedDB/IDBIndex.cpp
index bceaa98daf..c5b659ee24 100644
--- a/Libraries/LibWeb/IndexedDB/IDBIndex.cpp
+++ b/Libraries/LibWeb/IndexedDB/IDBIndex.cpp
@@ -102,11 +102,11 @@ JS::Value IDBIndex::key_path() const
 {
     return m_index->key_path().visit(
         [&](String const& value) -> JS::Value {
-            return JS::PrimitiveString::create(realm().vm(), value);
+            return JS::PrimitiveString::create(realm().vm(), Utf16String::from_utf8(value));
         },
         [&](Vector<String> const& value) -> JS::Value {
             return JS::Array::create_from<String>(realm(), value.span(), [&](auto const& entry) -> JS::Value {
-                return JS::PrimitiveString::create(realm().vm(), entry);
+                return JS::PrimitiveString::create(realm().vm(), Utf16String::from_utf8(entry));
             });
         });
 }
diff --git a/Libraries/LibWeb/IndexedDB/IDBObjectStore.cpp b/Libraries/LibWeb/IndexedDB/IDBObjectStore.cpp
index 45171dee54..36e2af133b 100644
--- a/Libraries/LibWeb/IndexedDB/IDBObjectStore.cpp
+++ b/Libraries/LibWeb/IndexedDB/IDBObjectStore.cpp
@@ -111,11 +111,11 @@ JS::Value IDBObjectStore::key_path() const
 
     return m_store->key_path().value().visit(
         [&](String const& value) -> JS::Value {
-            return JS::PrimitiveString::create(realm().vm(), value);
+            return JS::PrimitiveString::create(realm().vm(), Utf16String::from_utf8(value));
         },
         [&](Vector<String> const& value) -> JS::Value {
             return JS::Array::create_from<String>(realm(), value.span(), [&](auto const& entry) -> JS::Value {
-                return JS::PrimitiveString::create(realm().vm(), entry);
+                return JS::PrimitiveString::create(realm().vm(), Utf16String::from_utf8(entry));
             });
         });
 }
diff --git a/Libraries/LibWeb/IndexedDB/Internal/Algorithms.cpp b/Libraries/LibWeb/IndexedDB/Internal/Algorithms.cpp
index 6a3721667d..7657ef7c55 100644
--- a/Libraries/LibWeb/IndexedDB/Internal/Algorithms.cpp
+++ b/Libraries/LibWeb/IndexedDB/Internal/Algorithms.cpp
@@ -738,7 +738,7 @@ JS::Value convert_a_key_to_a_value(JS::Realm& realm, GC::Ref<Key> key)
 
     case Key::KeyType::String: {
         // Return an ECMAScript String value equal to value
-        return JS::PrimitiveString::create(realm.vm(), key->value_as_string());
+        return JS::PrimitiveString::create(realm.vm(), Utf16String::from_utf8(key->value_as_string()));
     }
 
     case Key::KeyType::Date: {
@@ -1062,13 +1062,13 @@ WebIDL::ExceptionOr<ErrorOr<JS::Value>> evaluate_key_path_on_a_value(JS::Realm&
         // If value is a Blob and identifier is "type"
         else if (value.is_object() && is<FileAPI::Blob>(value.as_object()) && identifier == "type") {
             // Let value be a String equal to value’s type.
-            value = JS::PrimitiveString::create(realm.vm(), static_cast<FileAPI::Blob&>(value.as_object()).type());
+            value = JS::PrimitiveString::create(realm.vm(), Utf16String::from_utf8(static_cast<FileAPI::Blob&>(value.as_object()).type()));
         }
 
         // If value is a File and identifier is "name"
         else if (value.is_object() && is<FileAPI::File>(value.as_object()) && identifier == "name") {
             // Let value be a String equal to value’s name.
-            value = JS::PrimitiveString::create(realm.vm(), static_cast<FileAPI::File&>(value.as_object()).name());
+            value = JS::PrimitiveString::create(realm.vm(), Utf16String::from_utf8(static_cast<FileAPI::File&>(value.as_object()).name()));
         }
 
         // If value is a File and identifier is "lastModified"
diff --git a/Libraries/LibWeb/Infra/JSON.cpp b/Libraries/LibWeb/Infra/JSON.cpp
index fbd6328658..f7dc1fd9c9 100644
--- a/Libraries/LibWeb/Infra/JSON.cpp
+++ b/Libraries/LibWeb/Infra/JSON.cpp
@@ -5,6 +5,7 @@
  */
 
 #include <AK/String.h>
+#include <AK/Utf16String.h>
 #include <LibJS/Runtime/AbstractOperations.h>
 #include <LibJS/Runtime/Array.h>
 #include <LibJS/Runtime/Completion.h>
@@ -21,7 +22,7 @@ WebIDL::ExceptionOr<JS::Value> parse_json_string_to_javascript_value(JS::Realm&
     auto& vm = realm.vm();
 
     // 1. Return ? Call(%JSON.parse%, undefined, « string »).
-    return TRY(JS::call(vm, *realm.intrinsics().json_parse_function(), JS::js_undefined(), JS::PrimitiveString::create(vm, string)));
+    return TRY(JS::call(vm, *realm.intrinsics().json_parse_function(), JS::js_undefined(), JS::PrimitiveString::create(vm, Utf16String::from_utf8(string))));
 }
 
 // https://infra.spec.whatwg.org/#parse-json-bytes-to-a-javascript-value
@@ -77,7 +78,7 @@ WebIDL::ExceptionOr<ByteBuffer> serialize_javascript_value_to_json_bytes(JS::VM&
             auto const& base_value = json_value.get<JSONBaseValue>();
 
             if (base_value.has<String>())
-                return JS::PrimitiveString::create(vm, base_value.get<String>());
+                return JS::PrimitiveString::create(vm, Utf16String::from_utf8(base_value.get<String>()));
 
             if (base_value.has<bool>())
                 return JS::Value(base_value.get<bool>());
diff --git a/Libraries/LibWeb/ServiceWorker/CacheStorage.cpp b/Libraries/LibWeb/ServiceWorker/CacheStorage.cpp
index 1ba2f15118..015b75c8d9 100644
--- a/Libraries/LibWeb/ServiceWorker/CacheStorage.cpp
+++ b/Libraries/LibWeb/ServiceWorker/CacheStorage.cpp
@@ -219,7 +219,7 @@ GC::Ref<WebIDL::Promise> CacheStorage::keys()
 
         // 2. Resolve promise with cacheKeys.
         WebIDL::resolve_promise(realm, promise, JS::Array::create_from<String>(realm, cache_keys, [&](String const& cache_key) {
-            return JS::PrimitiveString::create(realm.vm(), cache_key);
+            return JS::PrimitiveString::create(realm.vm(), Utf16String::from_utf8(cache_key));
         }));
     }));
 
diff --git a/Libraries/LibWeb/Streams/AbstractOperations.cpp b/Libraries/LibWeb/Streams/AbstractOperations.cpp
index 51f3cb837a..73d5fad8df 100644
--- a/Libraries/LibWeb/Streams/AbstractOperations.cpp
+++ b/Libraries/LibWeb/Streams/AbstractOperations.cpp
@@ -8,6 +8,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/Utf16String.h>
 #include <LibJS/Runtime/ArrayBuffer.h>
 #include <LibJS/Runtime/NativeFunction.h>
 #include <LibJS/Runtime/TypedArray.h>
@@ -117,7 +118,7 @@ WebIDL::ExceptionOr<void> pack_and_post_message(JS::Realm& realm, HTML::MessageP
     auto message = JS::Object::create(realm, nullptr);
 
     // 2. Perform ! CreateDataProperty(message, "type", type).
-    MUST(message->create_data_property(vm.names.type, JS::PrimitiveString::create(vm, type)));
+    MUST(message->create_data_property(vm.names.type, JS::PrimitiveString::create(vm, Utf16String::from_ascii_without_validation(type.bytes()))));
 
     // 3. Perform ! CreateDataProperty(message, "value", value).
     MUST(message->create_data_property(vm.names.value, value));
diff --git a/Libraries/LibWeb/WebAssembly/Memory.cpp b/Libraries/LibWeb/WebAssembly/Memory.cpp
index 4b2e3f9d44..3acbb22a47 100644
--- a/Libraries/LibWeb/WebAssembly/Memory.cpp
+++ b/Libraries/LibWeb/WebAssembly/Memory.cpp
@@ -139,7 +139,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::ArrayBuffer>> Memory::to_fixed_length_buffer()
         auto fixed_buffer = create_a_fixed_length_memory_buffer(vm, realm(), m_address, m_shared, *this);
 
         // 2. Perform ! DetachArrayBuffer(buffer, "WebAssembly.Memory").
-        MUST(JS::detach_array_buffer(vm, *m_buffer, JS::PrimitiveString::create(vm, "WebAssembly.Memory"_string)));
+        MUST(JS::detach_array_buffer(vm, *m_buffer, JS::PrimitiveString::create(vm, "WebAssembly.Memory"_utf16_fly_string)));
 
         // 3. Set this.[[BufferObject]] to fixedBuffer.
         m_buffer = fixed_buffer;
@@ -197,7 +197,7 @@ WebIDL::ExceptionOr<GC::Ref<JS::ArrayBuffer>> Memory::to_resizable_buffer()
     // 5. If IsSharedArrayBuffer(buffer) is false,
     // 9. Perform ! DetachArrayBuffer(buffer, "WebAssembly.Memory").
     if (!m_buffer->is_shared_array_buffer())
-        MUST(JS::detach_array_buffer(vm, *m_buffer, JS::PrimitiveString::create(vm, "WebAssembly.Memory"_string)));
+        MUST(JS::detach_array_buffer(vm, *m_buffer, JS::PrimitiveString::create(vm, "WebAssembly.Memory"_utf16_fly_string)));
 
     // 10. Set this.[[BufferObject]] to resizableBuffer.
     m_buffer = resizable_buffer;
@@ -225,7 +225,7 @@ void Memory::refresh_the_memory_buffer(JS::VM& vm, JS::Realm& realm, Wasm::Memor
         // 1. If IsSharedArrayBuffer(buffer) is false,
         if (!buffer->is_shared_array_buffer()) {
             // 1. Perform ! DetachArrayBuffer(buffer, "WebAssembly.Memory").
-            MUST(JS::detach_array_buffer(vm, *buffer, JS::PrimitiveString::create(vm, "WebAssembly.Memory"_string)));
+            MUST(JS::detach_array_buffer(vm, *buffer, JS::PrimitiveString::create(vm, "WebAssembly.Memory"_utf16_fly_string)));
         }
 
         // 2. Let newBuffer be the result of creating a fixed length memory buffer from memaddr.
@@ -301,7 +301,7 @@ GC::Ref<JS::ArrayBuffer> Memory::create_a_fixed_length_memory_buffer(JS::VM& vm,
     // 4. Otherwise,
     else {
         array_buffer = JS::ArrayBuffer::create(realm, JS::DataBlock::UnownedExternalBuffer(owner, &memory->data(), wasm_memory_buffer_data, wasm_memory_buffer_size));
-        array_buffer->set_detach_key(JS::PrimitiveString::create(vm, "WebAssembly.Memory"_string));
+        array_buffer->set_detach_key(JS::PrimitiveString::create(vm, "WebAssembly.Memory"_utf16_fly_string));
     }
 
     return GC::Ref(*array_buffer);
@@ -344,7 +344,7 @@ JS::ThrowCompletionOr<GC::Ref<JS::ArrayBuffer>> Memory::create_a_resizable_memor
         // AD-HOC: Set buffer.[[ArrayBufferDetachKey]] to "WebAssembly.Memory".
         //         SharedArrayBuffers can't be detached, but this allows us to bail early from HostGrowSharedArrayBuffer
         //         for SharedArrayBuffers not associated with a WebAssembly memory.
-        buffer->set_detach_key(JS::PrimitiveString::create(vm, "WebAssembly.Memory"_string));
+        buffer->set_detach_key(JS::PrimitiveString::create(vm, "WebAssembly.Memory"_utf16_fly_string));
 
         // 7. Return buffer.
         return buffer;
@@ -364,7 +364,7 @@ JS::ThrowCompletionOr<GC::Ref<JS::ArrayBuffer>> Memory::create_a_resizable_memor
         buffer->set_max_byte_length(max_size);
 
         // 8. Set buffer.[[ArrayBufferDetachKey]] to "WebAssembly.Memory".
-        buffer->set_detach_key(JS::PrimitiveString::create(vm, "WebAssembly.Memory"_string));
+        buffer->set_detach_key(JS::PrimitiveString::create(vm, "WebAssembly.Memory"_utf16_fly_string));
 
         // 9. Return buffer.
         return buffer;
diff --git a/Libraries/LibWeb/WebAssembly/WebAssembly.cpp b/Libraries/LibWeb/WebAssembly/WebAssembly.cpp
index 7e92e09ccd..b310f73f2c 100644
--- a/Libraries/LibWeb/WebAssembly/WebAssembly.cpp
+++ b/Libraries/LibWeb/WebAssembly/WebAssembly.cpp
@@ -532,7 +532,7 @@ JS::ThrowCompletionOr<JS::HandledByHost> host_resize_array_buffer(JS::VM& vm, JS
 {
     // 1. If buffer.[[ArrayBufferDetachKey]] is "WebAssembly.Memory",
     auto detach_key = buffer.detach_key();
-    if (detach_key.is_string() && detach_key.as_string() == JS::PrimitiveString::create(vm, "WebAssembly.Memory"_string)) {
+    if (detach_key.is_string() && detach_key.as_string() == JS::PrimitiveString::create(vm, "WebAssembly.Memory"_utf16_fly_string)) {
         // 1. Let map be the surrounding agent's associated Memory object cache.
         auto const& map = get_cache(*vm.current_realm()).memory_instances();
 
@@ -583,7 +583,7 @@ JS::ThrowCompletionOr<JS::HandledByHost> host_grow_shared_array_buffer(JS::VM& v
 {
     // AD-HOC: If buffer.[[ArrayBufferDetachKey]] is "WebAssembly.Memory",
     auto detach_key = buffer.detach_key();
-    if (detach_key.is_string() && detach_key.as_string() == JS::PrimitiveString::create(vm, "WebAssembly.Memory"_string)) {
+    if (detach_key.is_string() && detach_key.as_string() == JS::PrimitiveString::create(vm, "WebAssembly.Memory"_utf16_fly_string)) {
         // 1. Let map be the surrounding agent's associated Memory object cache.
         auto const& map = get_cache(*vm.current_realm()).memory_instances();
 
@@ -1224,77 +1224,77 @@ static JS::ThrowCompletionOr<GC::Ref<ClassName>> wasm_ordinary_create_from_const
     {                                                                                                                     \
     }
 
-#define DEFINE_WASM_NATIVE_ERROR_CONSTRUCTOR(ClassName, FullClassName, snake_name, PrototypeName, ConstructorName)                        \
-    GC_DEFINE_ALLOCATOR(ConstructorName);                                                                                                 \
-    ConstructorName::ConstructorName(JS::Realm& realm)                                                                                    \
-        : NativeFunction(#ClassName##_utf16_fly_string, *realm.intrinsics().error_constructor())                                          \
-    {                                                                                                                                     \
-    }                                                                                                                                     \
-                                                                                                                                          \
-    void ConstructorName::initialize(JS::Realm& realm)                                                                                    \
-    {                                                                                                                                     \
-        auto& vm = this->vm();                                                                                                            \
-        Base::initialize(realm);                                                                                                          \
-                                                                                                                                          \
-        /* 20.5.6.2.1 NativeError.prototype, https://tc39.es/ecma262/#sec-nativeerror.prototype */                                        \
-        define_direct_property(vm.names.prototype, &Bindings::ensure_web_prototype<PrototypeName>(realm, FullClassName##_fly_string), 0); \
-                                                                                                                                          \
-        define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, #ClassName##_string), JS::Attribute::Configurable);         \
-        define_direct_property(vm.names.length, JS::Value(1), JS::Attribute::Configurable);                                               \
-    }                                                                                                                                     \
-                                                                                                                                          \
-    ConstructorName::~ConstructorName() = default;                                                                                        \
-                                                                                                                                          \
-    /* 20.5.6.1.1 NativeError ( message [ , options ] ), https://tc39.es/ecma262/#sec-nativeerror */                                      \
-    JS::ThrowCompletionOr<JS::Value> ConstructorName::call()                                                                              \
-    {                                                                                                                                     \
-        /* 1. If NewTarget is undefined, let newTarget be the active function object; else let newTarget be NewTarget. */                 \
-        return TRY(construct(*this));                                                                                                     \
-    }                                                                                                                                     \
-                                                                                                                                          \
-    /* 20.5.6.1.1 NativeError ( message [ , options ] ), https://tc39.es/ecma262/#sec-nativeerror */                                      \
-    JS::ThrowCompletionOr<GC::Ref<JS::Object>> ConstructorName::construct(JS::FunctionObject& new_target)                                 \
-    {                                                                                                                                     \
-        auto& vm = this->vm();                                                                                                            \
-                                                                                                                                          \
-        auto message = vm.argument(0);                                                                                                    \
-        auto options = vm.argument(1);                                                                                                    \
-                                                                                                                                          \
-        /* 2. Let O be ? OrdinaryCreateFromConstructor(newTarget, "%NativeError.prototype%", « [[ErrorData]] »). */                       \
-        auto error = TRY(wasm_ordinary_create_from_constructor<ClassName, PrototypeName>(vm, new_target, FullClassName##_fly_string));    \
-                                                                                                                                          \
-        /* 3. If message is not undefined, then */                                                                                        \
-        if (!message.is_undefined()) {                                                                                                    \
-            /* a. Let msg be ? ToString(message). */                                                                                      \
-            auto msg = TRY(message.to_utf16_string(vm));                                                                                  \
-                                                                                                                                          \
-            /* b. Perform CreateNonEnumerableDataPropertyOrThrow(O, "message", msg). */                                                   \
-            error->create_non_enumerable_data_property_or_throw(vm.names.message, JS::PrimitiveString::create(vm, move(msg)));            \
-        }                                                                                                                                 \
-                                                                                                                                          \
-        /* 4. Perform ? InstallErrorCause(O, options). */                                                                                 \
-        TRY(error->install_error_cause(options));                                                                                         \
-                                                                                                                                          \
-        /* 5. Return O. */                                                                                                                \
-        return error;                                                                                                                     \
+#define DEFINE_WASM_NATIVE_ERROR_CONSTRUCTOR(ClassName, FullClassName, snake_name, PrototypeName, ConstructorName)                          \
+    GC_DEFINE_ALLOCATOR(ConstructorName);                                                                                                   \
+    ConstructorName::ConstructorName(JS::Realm& realm)                                                                                      \
+        : NativeFunction(#ClassName##_utf16_fly_string, *realm.intrinsics().error_constructor())                                            \
+    {                                                                                                                                       \
+    }                                                                                                                                       \
+                                                                                                                                            \
+    void ConstructorName::initialize(JS::Realm& realm)                                                                                      \
+    {                                                                                                                                       \
+        auto& vm = this->vm();                                                                                                              \
+        Base::initialize(realm);                                                                                                            \
+                                                                                                                                            \
+        /* 20.5.6.2.1 NativeError.prototype, https://tc39.es/ecma262/#sec-nativeerror.prototype */                                          \
+        define_direct_property(vm.names.prototype, &Bindings::ensure_web_prototype<PrototypeName>(realm, FullClassName##_fly_string), 0);   \
+                                                                                                                                            \
+        define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, #ClassName##_utf16_fly_string), JS::Attribute::Configurable); \
+        define_direct_property(vm.names.length, JS::Value(1), JS::Attribute::Configurable);                                                 \
+    }                                                                                                                                       \
+                                                                                                                                            \
+    ConstructorName::~ConstructorName() = default;                                                                                          \
+                                                                                                                                            \
+    /* 20.5.6.1.1 NativeError ( message [ , options ] ), https://tc39.es/ecma262/#sec-nativeerror */                                        \
+    JS::ThrowCompletionOr<JS::Value> ConstructorName::call()                                                                                \
+    {                                                                                                                                       \
+        /* 1. If NewTarget is undefined, let newTarget be the active function object; else let newTarget be NewTarget. */                   \
+        return TRY(construct(*this));                                                                                                       \
+    }                                                                                                                                       \
+                                                                                                                                            \
+    /* 20.5.6.1.1 NativeError ( message [ , options ] ), https://tc39.es/ecma262/#sec-nativeerror */                                        \
+    JS::ThrowCompletionOr<GC::Ref<JS::Object>> ConstructorName::construct(JS::FunctionObject& new_target)                                   \
+    {                                                                                                                                       \
+        auto& vm = this->vm();                                                                                                              \
+                                                                                                                                            \
+        auto message = vm.argument(0);                                                                                                      \
+        auto options = vm.argument(1);                                                                                                      \
+                                                                                                                                            \
+        /* 2. Let O be ? OrdinaryCreateFromConstructor(newTarget, "%NativeError.prototype%", « [[ErrorData]] »). */                         \
+        auto error = TRY(wasm_ordinary_create_from_constructor<ClassName, PrototypeName>(vm, new_target, FullClassName##_fly_string));      \
+                                                                                                                                            \
+        /* 3. If message is not undefined, then */                                                                                          \
+        if (!message.is_undefined()) {                                                                                                      \
+            /* a. Let msg be ? ToString(message). */                                                                                        \
+            auto msg = TRY(message.to_utf16_string(vm));                                                                                    \
+                                                                                                                                            \
+            /* b. Perform CreateNonEnumerableDataPropertyOrThrow(O, "message", msg). */                                                     \
+            error->create_non_enumerable_data_property_or_throw(vm.names.message, JS::PrimitiveString::create(vm, move(msg)));              \
+        }                                                                                                                                   \
+                                                                                                                                            \
+        /* 4. Perform ? InstallErrorCause(O, options). */                                                                                   \
+        TRY(error->install_error_cause(options));                                                                                           \
+                                                                                                                                            \
+        /* 5. Return O. */                                                                                                                  \
+        return error;                                                                                                                       \
     }
 
-#define DEFINE_WASM_NATIVE_ERROR_PROTOTYPE(ClassName, FullClassName, snake_name, PrototypeName, ConstructorName) \
-    GC_DEFINE_ALLOCATOR(PrototypeName);                                                                          \
-                                                                                                                 \
-    PrototypeName::PrototypeName(JS::Realm& realm)                                                               \
-        : PrototypeObject(realm.intrinsics().error_prototype())                                                  \
-    {                                                                                                            \
-    }                                                                                                            \
-                                                                                                                 \
-    void PrototypeName::initialize(JS::Realm& realm)                                                             \
-    {                                                                                                            \
-        auto& vm = this->vm();                                                                                   \
-        Base::initialize(realm);                                                                                 \
-                                                                                                                 \
-        u8 const attr = JS::Attribute::Writable | JS::Attribute::Configurable;                                   \
-        define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, #ClassName##_string), attr);       \
-        define_direct_property(vm.names.message, JS::PrimitiveString::create(vm, Utf16String {}), attr);         \
+#define DEFINE_WASM_NATIVE_ERROR_PROTOTYPE(ClassName, FullClassName, snake_name, PrototypeName, ConstructorName)     \
+    GC_DEFINE_ALLOCATOR(PrototypeName);                                                                              \
+                                                                                                                     \
+    PrototypeName::PrototypeName(JS::Realm& realm)                                                                   \
+        : PrototypeObject(realm.intrinsics().error_prototype())                                                      \
+    {                                                                                                                \
+    }                                                                                                                \
+                                                                                                                     \
+    void PrototypeName::initialize(JS::Realm& realm)                                                                 \
+    {                                                                                                                \
+        auto& vm = this->vm();                                                                                       \
+        Base::initialize(realm);                                                                                     \
+                                                                                                                     \
+        u8 const attr = JS::Attribute::Writable | JS::Attribute::Configurable;                                       \
+        define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, #ClassName##_utf16_fly_string), attr); \
+        define_direct_property(vm.names.message, JS::PrimitiveString::create(vm, Utf16String {}), attr);             \
     }
 
 #define __WASM_ENUMERATE(ClassName, FullClassName, snake_name, PrototypeName, ConstructorName) \
diff --git a/Libraries/LibWeb/WebDriver/JSON.cpp b/Libraries/LibWeb/WebDriver/JSON.cpp
index f454862ec7..504d62bd5d 100644
--- a/Libraries/LibWeb/WebDriver/JSON.cpp
+++ b/Libraries/LibWeb/WebDriver/JSON.cpp
@@ -105,7 +105,7 @@ static JS::Value json_value_to_js_value(JS::VM& vm, JsonValue const& value)
     if (auto double_value = value.get_double_with_precision_loss(); double_value.has_value())
         return JS::Value(double_value.value());
     if (value.is_string())
-        return JS::PrimitiveString::create(vm, value.as_string());
+        return JS::PrimitiveString::create(vm, Utf16String::from_utf8(value.as_string()));
     if (value.is_bool())
         return JS::Value(value.as_bool());
     VERIFY_NOT_REACHED();
diff --git a/Libraries/LibWeb/WebGL/WebGLRenderingContextImpl.cpp b/Libraries/LibWeb/WebGL/WebGLRenderingContextImpl.cpp
index c45bbfe3b7..d703ec89d6 100644
--- a/Libraries/LibWeb/WebGL/WebGLRenderingContextImpl.cpp
+++ b/Libraries/LibWeb/WebGL/WebGLRenderingContextImpl.cpp
@@ -12,6 +12,8 @@ extern "C" {
 #include <GLES2/gl2ext_angle.h>
 }
 
+#include <AK/StringView.h>
+#include <AK/Utf16String.h>
 #include <LibJS/Runtime/Array.h>
 #include <LibJS/Runtime/ArrayBuffer.h>
 #include <LibJS/Runtime/DataView.h>
@@ -1118,7 +1120,7 @@ WebIDL::ExceptionOr<JS::Value> WebGLRenderingContextImpl::get_parameter(WebIDL::
     }
     case GL_RENDERER: {
         auto result = reinterpret_cast<char const*>(m_context->get_string(GL_RENDERER));
-        return JS::PrimitiveString::create(realm().vm(), ByteString { result });
+        return JS::PrimitiveString::create(realm().vm(), Utf16String::from_ascii_without_validation(StringView { result, strlen(result) }.bytes()));
     }
     case GL_SAMPLE_ALPHA_TO_COVERAGE: {
         GLboolean result { GL_FALSE };
@@ -1166,7 +1168,7 @@ WebIDL::ExceptionOr<JS::Value> WebGLRenderingContextImpl::get_parameter(WebIDL::
     }
     case GL_SHADING_LANGUAGE_VERSION: {
         auto result = reinterpret_cast<char const*>(m_context->get_string(GL_SHADING_LANGUAGE_VERSION));
-        return JS::PrimitiveString::create(realm().vm(), ByteString { result });
+        return JS::PrimitiveString::create(realm().vm(), Utf16String::from_ascii_without_validation(StringView { result, strlen(result) }.bytes()));
     }
     case GL_STENCIL_BACK_FAIL: {
         GLint result { 0 };
@@ -1275,11 +1277,11 @@ WebIDL::ExceptionOr<JS::Value> WebGLRenderingContextImpl::get_parameter(WebIDL::
     }
     case GL_VENDOR: {
         auto result = reinterpret_cast<char const*>(m_context->get_string(GL_VENDOR));
-        return JS::PrimitiveString::create(realm().vm(), ByteString { result });
+        return JS::PrimitiveString::create(realm().vm(), Utf16String::from_ascii_without_validation(StringView { result, strlen(result) }.bytes()));
     }
     case GL_VERSION: {
         auto result = reinterpret_cast<char const*>(m_context->get_string(GL_VERSION));
-        return JS::PrimitiveString::create(realm().vm(), ByteString { result });
+        return JS::PrimitiveString::create(realm().vm(), Utf16String::from_ascii_without_validation(StringView { result, strlen(result) }.bytes()));
     }
     case GL_VIEWPORT: {
         Array<GLint, 4> result;
@@ -1297,7 +1299,7 @@ WebIDL::ExceptionOr<JS::Value> WebGLRenderingContextImpl::get_parameter(WebIDL::
             return JS::js_null();
         }
         auto result = reinterpret_cast<char const*>(m_context->get_string(GL_VENDOR));
-        return JS::PrimitiveString::create(realm().vm(), ByteString { result });
+        return JS::PrimitiveString::create(realm().vm(), Utf16String::from_ascii_without_validation(StringView { result, strlen(result) }.bytes()));
     }
     case UNMASKED_RENDERER_WEBGL: {
         if (!extension_enabled("WEBGL_debug_renderer_info"sv)) {
@@ -1305,7 +1307,7 @@ WebIDL::ExceptionOr<JS::Value> WebGLRenderingContextImpl::get_parameter(WebIDL::
             return JS::js_null();
         }
         auto result = reinterpret_cast<char const*>(m_context->get_string(GL_RENDERER));
-        return JS::PrimitiveString::create(realm().vm(), ByteString { result });
+        return JS::PrimitiveString::create(realm().vm(), Utf16String::from_ascii_without_validation(StringView { result, strlen(result) }.bytes()));
     }
 
     case GL_FRAGMENT_SHADER_DERIVATIVE_HINT: { // NOTE: This has the same value as GL_FRAGMENT_SHADER_DERIVATIVE_HINT_OES
diff --git a/Libraries/LibWeb/WebIDL/AbstractOperations.h b/Libraries/LibWeb/WebIDL/AbstractOperations.h
index 936dbf3b29..51da907674 100644
--- a/Libraries/LibWeb/WebIDL/AbstractOperations.h
+++ b/Libraries/LibWeb/WebIDL/AbstractOperations.h
@@ -10,11 +10,13 @@
 
 #include <AK/FlyString.h>
 #include <AK/Forward.h>
+#include <AK/Utf16String.h>
 #include <LibGC/Ptr.h>
 #include <LibGC/RootVector.h>
 #include <LibJS/Forward.h>
 #include <LibJS/Runtime/AbstractOperations.h>
 #include <LibJS/Runtime/FunctionObject.h>
+#include <LibJS/Runtime/PrimitiveString.h>
 #include <LibWeb/Bindings/Intrinsics.h>
 #include <LibWeb/Export.h>
 #include <LibWeb/Forward.h>
@@ -36,6 +38,16 @@ WEB_API JS::ThrowCompletionOr<String> to_usv_string(JS::VM&, JS::Value);
 JS::ThrowCompletionOr<Utf16String> to_utf16_usv_string(JS::VM&, JS::Value);
 JS::ThrowCompletionOr<String> to_byte_string(JS::VM&, JS::Value);
 
+template<typename T>
+GC::Ref<JS::PrimitiveString> primitive_string_from_string(JS::VM& vm, T&& value)
+{
+    using ValueType = RemoveCVReference<T>;
+    if constexpr (IsSame<ValueType, String> || IsSame<ValueType, StringView> || IsSame<ValueType, FlyString> || IsSame<ValueType, ByteString>)
+        return JS::PrimitiveString::create(vm, Utf16String::from_utf8(value));
+    else
+        return JS::PrimitiveString::create(vm, forward<T>(value));
+}
+
 enum class ExceptionBehavior {
     NotSpecified,
     Report,
diff --git a/Libraries/LibWeb/WebSockets/WebSocket.cpp b/Libraries/LibWeb/WebSockets/WebSocket.cpp
index 4f1679d99f..dd2d2478c2 100644
--- a/Libraries/LibWeb/WebSockets/WebSocket.cpp
+++ b/Libraries/LibWeb/WebSockets/WebSocket.cpp
@@ -6,6 +6,7 @@
  */
 
 #include <AK/QuickSort.h>
+#include <AK/Utf16String.h>
 #include <LibJS/Runtime/ArrayBuffer.h>
 #include <LibJS/Runtime/FunctionObject.h>
 #include <LibRequests/RequestClient.h>
@@ -378,9 +379,8 @@ void WebSocket::on_message(ByteBuffer message, bool is_text)
     // When a WebSocket message has been received with type type and data data, the user agent must queue a task to follow these steps:
     HTML::queue_a_task(HTML::Task::Source::WebSocket, nullptr, nullptr, GC::create_function(heap(), [this, message = move(message), is_text] {
         if (is_text) {
-            auto text_message = ByteString(ReadonlyBytes(message));
             Bindings::MessageEventInit event_init;
-            event_init.data = JS::PrimitiveString::create(vm(), text_message);
+            event_init.data = JS::PrimitiveString::create(vm(), Utf16String::from_utf8(StringView { ReadonlyBytes(message) }));
             dispatch_event(HTML::MessageEvent::create(realm(), HTML::EventNames::message, event_init, m_url.origin()));
             return;
         }
diff --git a/Libraries/LibWeb/XHR/FormDataIterator.cpp b/Libraries/LibWeb/XHR/FormDataIterator.cpp
index f168721fdb..7341444916 100644
--- a/Libraries/LibWeb/XHR/FormDataIterator.cpp
+++ b/Libraries/LibWeb/XHR/FormDataIterator.cpp
@@ -61,20 +61,20 @@ JS::Object* FormDataIterator::next()
 
     auto entry = m_form_data->m_entry_list[m_index++];
     if (m_iterator_kind == JS::Object::PropertyKind::Key)
-        return create_iterator_result_object(vm, JS::PrimitiveString::create(vm, entry.name), false);
+        return create_iterator_result_object(vm, JS::PrimitiveString::create(vm, Utf16String::from_utf8(entry.name)), false);
 
     auto entry_value = entry.value.visit(
         [&](GC::Ref<FileAPI::File> file) -> JS::Value {
             return file;
         },
         [&](String const& string) -> JS::Value {
-            return JS::PrimitiveString::create(vm, string);
+            return JS::PrimitiveString::create(vm, Utf16String::from_utf8(string));
         });
 
     if (m_iterator_kind == JS::Object::PropertyKind::Value)
         return create_iterator_result_object(vm, entry_value, false);
 
-    return create_iterator_result_object(vm, JS::Array::create_from(realm(), { JS::PrimitiveString::create(vm, entry.name), entry_value }), false).ptr();
+    return create_iterator_result_object(vm, JS::Array::create_from(realm(), { JS::PrimitiveString::create(vm, Utf16String::from_utf8(entry.name)), entry_value }), false).ptr();
 }
 
 }
diff --git a/Libraries/LibWeb/XHR/XMLHttpRequest.cpp b/Libraries/LibWeb/XHR/XMLHttpRequest.cpp
index 45d9e19840..34f9b4497d 100644
--- a/Libraries/LibWeb/XHR/XMLHttpRequest.cpp
+++ b/Libraries/LibWeb/XHR/XMLHttpRequest.cpp
@@ -194,10 +194,10 @@ WebIDL::ExceptionOr<JS::Value> XMLHttpRequest::response()
     if (m_response_type == Bindings::XMLHttpRequestResponseType::Empty || m_response_type == Bindings::XMLHttpRequestResponseType::Text) {
         // 1. If this’s state is not loading or done, then return the empty string.
         if (m_state != State::Loading && m_state != State::Done)
-            return JS::PrimitiveString::create(vm, String {});
+            return JS::PrimitiveString::create(vm, Utf16String {});
 
         // 2. Return the result of getting a text response for this.
-        return JS::PrimitiveString::create(vm, get_text_response());
+        return JS::PrimitiveString::create(vm, Utf16String::from_utf8(get_text_response()));
     }
     // 2. If this’s state is not done, then return null.
     if (m_state != State::Done)
diff --git a/Meta/Generators/generate_libweb_css_style_properties.py b/Meta/Generators/generate_libweb_css_style_properties.py
index 78f38dfd8e..c8705c0f38 100644
--- a/Meta/Generators/generate_libweb_css_style_properties.py
+++ b/Meta/Generators/generate_libweb_css_style_properties.py
@@ -55,6 +55,7 @@ def write_implementation_file(out: TextIO, properties: dict) -> None:
 #include <LibJS/Runtime/Object.h>
 #include <LibJS/Runtime/PrimitiveString.h>
 #include <LibJS/Runtime/ValueInlines.h>
+#include <AK/Utf16String.h>
 #include <LibWeb/Bindings/ExceptionOrUtils.h>
 #include <LibWeb/Bindings/MainThreadVM.h>
 #include <LibWeb/CSS/GeneratedCSSStyleProperties.h>
@@ -90,7 +91,7 @@ GC::Ref<JS::NativeFunction> create_getter(JS::Realm& realm, Utf16FlyString const
         auto result = TRY(throw_dom_exception_if_needed(vm, [&] {
             return idl_object->get_property_value(property_name);
         }));
-        return JS::PrimitiveString::create(vm, result);
+        return JS::PrimitiveString::create(vm, Utf16String::from_utf8(result));
     };
 
     return JS::NativeFunction::create(realm, move(getter), 0, JS::PropertyKey { attribute_name }, &realm, "get"sv);
diff --git a/Meta/Generators/libweb_bindings/callback_interfaces.py b/Meta/Generators/libweb_bindings/callback_interfaces.py
index 341f379cc6..b5ad15e65a 100644
--- a/Meta/Generators/libweb_bindings/callback_interfaces.py
+++ b/Meta/Generators/libweb_bindings/callback_interfaces.py
@@ -50,7 +50,7 @@ def write_callback_interface_implementation(
     [[maybe_unused]] u8 default_attributes = JS::Attribute::Enumerable;
 
     object.define_direct_property(vm.names.length, JS::Value(0), JS::Attribute::Configurable);
-    object.define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, "{interface.name}"_string), JS::Attribute::Configurable);
+    object.define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, "{interface.name}"_utf16), JS::Attribute::Configurable);
 """)
     define_the_constants(out, context, includes, interface)
     out.write(
diff --git a/Meta/Generators/libweb_bindings/interfaces.py b/Meta/Generators/libweb_bindings/interfaces.py
index 5005a34d37..c79c1fa101 100644
--- a/Meta/Generators/libweb_bindings/interfaces.py
+++ b/Meta/Generators/libweb_bindings/interfaces.py
@@ -138,7 +138,7 @@ def write_implementation(
 
     {f'object.set_prototype(&ensure_web_constructor<{interface.parent_name}Prototype>(realm, "{interface.parent_name}"_fly_string));' if interface.parent_name else ""}
     object.define_direct_property(vm.names.length, JS::Value({constructor_length}), JS::Attribute::Configurable);
-    object.define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, "{interface.name}"_string), JS::Attribute::Configurable);
+    object.define_direct_property(vm.names.name, JS::PrimitiveString::create(vm, "{interface.name}"_utf16), JS::Attribute::Configurable);
     object.define_direct_property(vm.names.prototype, &ensure_web_prototype<{interface.prototype_class}>(realm, "{interface.namespaced_name}"_fly_string), 0);
 """)
     constants.define_the_constants(out, context, includes, interface)
@@ -214,7 +214,7 @@ void {interface.prototype_class}::initialize(JS::Realm& realm)
 
     if "Global" in interface.extended_attributes:
         out.write(
-            f'    object.define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, "{interface.namespaced_name}"_string), JS::Attribute::Configurable);\n'
+            f'    object.define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, "{interface.namespaced_name}"_utf16), JS::Attribute::Configurable);\n'
         )
         if interface_requires_custom_prototype(interface):
             out.write("    Base::initialize(realm);\n")
@@ -244,7 +244,7 @@ void {interface.prototype_class}::initialize(JS::Realm& realm)
     constants.define_the_constants(out, context, includes, interface)
     operations.define_unscopable_members(out, includes, interface)
     out.write(
-        f'    object.define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, "{interface.namespaced_name}"_string), JS::Attribute::Configurable);\n'
+        f'    object.define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, "{interface.namespaced_name}"_utf16), JS::Attribute::Configurable);\n'
     )
     if interface_requires_custom_prototype(interface):
         out.write("    Base::initialize(realm);\n")
diff --git a/Meta/Generators/libweb_bindings/iterables.py b/Meta/Generators/libweb_bindings/iterables.py
index e5a4fb208b..7ae2d1fe0f 100644
--- a/Meta/Generators/libweb_bindings/iterables.py
+++ b/Meta/Generators/libweb_bindings/iterables.py
@@ -282,7 +282,7 @@ void {interface.name}IteratorPrototype::initialize(JS::Realm& realm)
     auto& vm = this->vm();
     Base::initialize(realm);
     define_native_function(realm, vm.names.next, next, 0, JS::Attribute::Writable | JS::Attribute::Enumerable | JS::Attribute::Configurable);
-    define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, "{interface.name} Iterator"_string), JS::Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, "{interface.name} Iterator"_utf16), JS::Attribute::Configurable);
 }}
 
 static JS::ThrowCompletionOr<{fully_qualified_name_for_interface(interface)}Iterator*> {make_name_acceptable_cpp(title_case_to_snake_case(iterator_interface_name))}_impl_from(JS::VM& vm)
@@ -373,7 +373,7 @@ void {interface.name}AsyncIteratorPrototype::initialize(JS::Realm& realm)
 {{
     auto& vm = this->vm();
     Base::initialize(realm);
-    define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, "{interface.name} AsyncIterator"_string), JS::Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, "{interface.name} AsyncIterator"_utf16), JS::Attribute::Configurable);
 
     define_native_function(realm, vm.names.next, next, 0, JS::default_attributes);
     {"define_native_function(realm, vm.names.return_, return_, 1, JS::default_attributes);" if "DefinesAsyncIteratorReturn" in interface.extended_attributes else ""}
diff --git a/Meta/Generators/libweb_bindings/named_and_indexed_properties.py b/Meta/Generators/libweb_bindings/named_and_indexed_properties.py
index 7f6d804718..c64b4adcc9 100644
--- a/Meta/Generators/libweb_bindings/named_and_indexed_properties.py
+++ b/Meta/Generators/libweb_bindings/named_and_indexed_properties.py
@@ -96,7 +96,7 @@ void {interface.name}Properties::initialize(JS::Realm& realm)
     auto& vm = realm.vm();
 
     // The class string of a named properties object is the concatenation of the interface's identifier and the string "Properties".
-    define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, "{interface.name}Properties"_string), JS::Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, "{interface.name}Properties"_utf16), JS::Attribute::Configurable);
 
     // 1. Let proto be null.
     // 2. If interface is declared to inherit from another interface, then set proto to the interface prototype object in realm for the inherited interface.
diff --git a/Meta/Generators/libweb_bindings/namespaces.py b/Meta/Generators/libweb_bindings/namespaces.py
index 7f80549c00..cda644dbbc 100644
--- a/Meta/Generators/libweb_bindings/namespaces.py
+++ b/Meta/Generators/libweb_bindings/namespaces.py
@@ -95,7 +95,7 @@ void {interface.namespace_class}::initialize(JS::Realm& realm)
     Base::initialize(realm);
 
     // The class string of a namespace object is the namespace’s identifier.
-    define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, "{interface.name}"_string), JS::Attribute::Configurable);
+    define_direct_property(vm.well_known_symbol_to_string_tag(), JS::PrimitiveString::create(vm, "{interface.name}"_utf16), JS::Attribute::Configurable);
 """
     )
 
diff --git a/Meta/Generators/libweb_bindings/to_js_value.py b/Meta/Generators/libweb_bindings/to_js_value.py
index 675ac8a88a..c7756d68ae 100644
--- a/Meta/Generators/libweb_bindings/to_js_value.py
+++ b/Meta/Generators/libweb_bindings/to_js_value.py
@@ -41,9 +41,9 @@ def write_enumeration_to_javascript_value_declaration(
     enumeration: Enumeration,
     includes: GeneratedIncludes,
 ) -> None:
-    includes.add("AK/String.h")
+    includes.add("AK/Utf16String.h")
 
-    out.write(f"String idl_enum_to_string({enumeration.name});\n\n")
+    out.write(f"Utf16String idl_enum_to_string({enumeration.name});\n\n")
 
 
 def write_dictionary_to_javascript_value_declaration(out: TextIO, dictionary: Dictionary) -> None:
@@ -56,7 +56,7 @@ def write_dictionary_to_javascript_value_declaration(out: TextIO, dictionary: Di
 def write_enumeration_to_javascript_value_conversion(out: TextIO, enumeration: Enumeration) -> None:
     out.write(
         f"""// https://webidl.spec.whatwg.org/#idl-enumeration
-String idl_enum_to_string({enumeration.name} value)
+Utf16String idl_enum_to_string({enumeration.name} value)
 {{
     // The result of converting an IDL enumeration type value to a JavaScript value is the String value that represents the same sequence of code units as the enumeration value.
     switch (value) {{
@@ -65,7 +65,7 @@ String idl_enum_to_string({enumeration.name} value)
 
     for value in enumeration.values:
         out.write(f"    case {enumeration.name}::{string_to_cpp_enum_name(value)}:\n")
-        out.write(f'        return "{value}"_string;\n')
+        out.write(f'        return "{value}"_utf16;\n')
 
     out.write(
         """    }
@@ -212,23 +212,23 @@ def unrestricted_double_to_javascript_value(value: str) -> str:
 
 # 3.2.10. DOMString, https://webidl.spec.whatwg.org/#js-DOMString
 def domstring_to_javascript_value(value: str, includes: GeneratedIncludes) -> str:
-    includes.add("LibJS/Runtime/PrimitiveString.h")
-    return f"JS::PrimitiveString::create(vm, {value})"
+    includes.add("LibWeb/WebIDL/AbstractOperations.h")
+    return f"WebIDL::primitive_string_from_string(vm, {value})"
 
 
 # 3.2.11. ByteString, https://webidl.spec.whatwg.org/#js-ByteString
 def bytestring_to_javascript_value(value: str, includes: GeneratedIncludes) -> str:
-    includes.add("LibJS/Runtime/PrimitiveString.h")
+    includes.add("LibWeb/WebIDL/AbstractOperations.h")
     # The result of converting an IDL ByteString value to a JavaScript value is a String value whose length is the length
     # of the ByteString, and the value of each element of which is the value of the corresponding element of the ByteString.
-    return f"JS::PrimitiveString::create(vm, {value})"
+    return f"WebIDL::primitive_string_from_string(vm, {value})"
 
 
 # 3.2.12. USVString, https://webidl.spec.whatwg.org/#js-USVString
 def usvstring_to_javascript_value(value: str, includes: GeneratedIncludes) -> str:
-    includes.add("LibJS/Runtime/PrimitiveString.h")
+    includes.add("LibWeb/WebIDL/AbstractOperations.h")
     # The result of converting an IDL USVString value S to a JavaScript value is S.
-    return f"JS::PrimitiveString::create(vm, {value})"
+    return f"WebIDL::primitive_string_from_string(vm, {value})"
 
 
 # 3.2.13. object, https://webidl.spec.whatwg.org/#js-object
diff --git a/Services/WebContent/DevToolsConsoleClient.cpp b/Services/WebContent/DevToolsConsoleClient.cpp
index 912fc7566e..b3ee478c8c 100644
--- a/Services/WebContent/DevToolsConsoleClient.cpp
+++ b/Services/WebContent/DevToolsConsoleClient.cpp
@@ -86,7 +86,7 @@ static JsonValue serialize_js_value(JS::Realm& realm, JS::Value value)
         Web::HTML::TemporaryExecutionContext execution_context { realm };
         AllocatingMemoryStream stream;
 
-        JS::PrintContext context { vm, stream, true };
+        JS::PrintContext context { .vm = vm, .stream = &stream, .strip_ansi = true };
         MUST(JS::print(value, context));
 
         return MUST(String::from_stream(stream, stream.used_buffer_size()));
@@ -151,7 +151,7 @@ JS::ThrowCompletionOr<JS::Value> DevToolsConsoleClient::printer(JS::Console::Log
 
         for (auto const& frame : trace.stack) {
             stack_frames.unchecked_append(WebView::StackFrame {
-                .function = frame.function_name,
+                .function = frame.function_name.to_utf8(),
                 .file = frame.source_file,
                 .line = frame.line,
                 .column = frame.column,
diff --git a/Tests/AK/TestBase64.cpp b/Tests/AK/TestBase64.cpp
index 90cb371f5f..54c5cb40ac 100644
--- a/Tests/AK/TestBase64.cpp
+++ b/Tests/AK/TestBase64.cpp
@@ -122,6 +122,10 @@ TEST_CASE(test_encode)
     auto encode_equal = [&](StringView input, StringView expected) {
         auto encoded = MUST(encode_base64(input.bytes()));
         EXPECT_EQ(encoded, expected);
+
+        auto encoded_utf16 = MUST(encode_base64_to_utf16(input.bytes()));
+        EXPECT(encoded_utf16.has_ascii_storage());
+        EXPECT_EQ(encoded_utf16.ascii_view(), expected);
     };
 
     encode_equal(""sv, ""sv);
@@ -138,6 +142,10 @@ TEST_CASE(test_encode_omit_padding)
     auto encode_equal = [&](StringView input, StringView expected) {
         auto encoded = MUST(encode_base64(input.bytes(), AK::OmitPadding::Yes));
         EXPECT_EQ(encoded, expected);
+
+        auto encoded_utf16 = MUST(encode_base64_to_utf16(input.bytes(), AK::OmitPadding::Yes));
+        EXPECT(encoded_utf16.has_ascii_storage());
+        EXPECT_EQ(encoded_utf16.ascii_view(), expected);
     };
 
     encode_equal(""sv, ""sv);
@@ -175,6 +183,10 @@ TEST_CASE(test_urlencode)
     auto encode_equal = [&](StringView input, StringView expected) {
         auto encoded = MUST(encode_base64url(input.bytes()));
         EXPECT_EQ(encoded, expected);
+
+        auto encoded_utf16 = MUST(encode_base64url_to_utf16(input.bytes()));
+        EXPECT(encoded_utf16.has_ascii_storage());
+        EXPECT_EQ(encoded_utf16.ascii_view(), expected);
     };
 
     encode_equal(""sv, ""sv);
@@ -196,6 +208,10 @@ TEST_CASE(test_urlencode_omit_padding)
     auto encode_equal = [&](StringView input, StringView expected) {
         auto encoded = MUST(encode_base64url(input.bytes(), AK::OmitPadding::Yes));
         EXPECT_EQ(encoded, expected);
+
+        auto encoded_utf16 = MUST(encode_base64url_to_utf16(input.bytes(), AK::OmitPadding::Yes));
+        EXPECT(encoded_utf16.has_ascii_storage());
+        EXPECT_EQ(encoded_utf16.ascii_view(), expected);
     };
 
     encode_equal(""sv, ""sv);
diff --git a/Tests/LibCrypto/TestBigFraction.cpp b/Tests/LibCrypto/TestBigFraction.cpp
index a3c19c3ec0..a4a7601a6b 100644
--- a/Tests/LibCrypto/TestBigFraction.cpp
+++ b/Tests/LibCrypto/TestBigFraction.cpp
@@ -36,7 +36,7 @@ TEST_CASE(roundtrip_from_string)
     for (auto valid_number_string : valid_number_strings) {
         auto result = TRY_OR_FAIL(Crypto::BigFraction::from_string(valid_number_string));
         auto precision = valid_number_string.length() - valid_number_string.find('.').value();
-        EXPECT_EQ(result.to_string(precision), valid_number_string);
+        EXPECT_EQ(result.to_utf16_string(precision), Utf16String::from_utf8(valid_number_string));
     }
 }
 
diff --git a/Tests/LibJS/Runtime/builtins/JSON/JSON.stringify.js b/Tests/LibJS/Runtime/builtins/JSON/JSON.stringify.js
index 97bc5541f2..dbba985683 100644
--- a/Tests/LibJS/Runtime/builtins/JSON/JSON.stringify.js
+++ b/Tests/LibJS/Runtime/builtins/JSON/JSON.stringify.js
@@ -105,6 +105,7 @@ describe("correct behavior", () => {
         expect(JSON.stringify({ a: function () {} })).toBe("{}");
         expect(JSON.stringify({ a: Symbol() })).toBe("{}");
         expect(JSON.stringify({ a: 1, b: undefined, c: 2 })).toBe('{"a":1,"c":2}');
+        expect(JSON.stringify({ a: "é", b: undefined, c: 1 })).toBe('{"a":"é","c":1}');
     });
 
     test("array replacer acts as property whitelist", () => {
diff --git a/Tests/LibJS/Runtime/builtins/Number/Number.prototype.toString.js b/Tests/LibJS/Runtime/builtins/Number/Number.prototype.toString.js
index 5e1d5e5402..b0181b3ca3 100644
--- a/Tests/LibJS/Runtime/builtins/Number/Number.prototype.toString.js
+++ b/Tests/LibJS/Runtime/builtins/Number/Number.prototype.toString.js
@@ -66,6 +66,10 @@ describe("correct behavior", () => {
         });
     });
 
+    test("fractional number with radix", () => {
+        expect((0.5).toString(2)).toBe("0.1");
+    });
+
     test("decimal radix gets converted to int", () => {
         expect((30).toString(10.1)).toBe("30");
         expect((30).toString(10.9)).toBe("30");
diff --git a/Tests/LibJS/test-js.cpp b/Tests/LibJS/test-js.cpp
index 0e2538d0c0..886389718f 100644
--- a/Tests/LibJS/test-js.cpp
+++ b/Tests/LibJS/test-js.cpp
@@ -42,7 +42,7 @@ TESTJS_GLOBAL_FUNCTION(evaluate_source, evaluateSource)
 
     auto script = JS::Script::parse(source.utf16_view(), realm);
     if (script.is_error())
-        return vm.throw_completion<JS::SyntaxError>(script.error().first().to_string());
+        return vm.throw_completion<JS::SyntaxError>(script.error().first().to_utf16_string());
 
     return vm.run(script.value());
 }
@@ -54,7 +54,7 @@ TESTJS_GLOBAL_FUNCTION(evaluate_module, evaluateModule)
     auto path = TRY(vm.argument(0).to_utf16_string(vm)).to_utf8_but_should_be_ported_to_utf16();
     auto module = Test::JS::parse_module(path.to_byte_string(), realm);
     if (module.is_error())
-        return vm.throw_completion<JS::SyntaxError>(module.error().error.to_string());
+        return vm.throw_completion<JS::SyntaxError>(module.error().error.to_utf16_string());
 
     return vm.run(module.value());
 }
@@ -154,14 +154,15 @@ TESTJS_GLOBAL_FUNCTION(detach_array_buffer, detachArrayBuffer)
 
 TESTJS_GLOBAL_FUNCTION(set_time_zone, setTimeZone)
 {
-    auto current_time_zone = JS::PrimitiveString::create(vm, Core::TimeZone::current_time_zone());
+    auto current_time_zone = Core::TimeZone::current_time_zone();
+    auto current_time_zone_string = JS::PrimitiveString::create(vm, Utf16String::from_ascii_without_validation(current_time_zone.bytes_as_string_view().bytes()));
     auto time_zone = TRY(vm.argument(0).to_utf16_string(vm)).to_utf8_but_should_be_ported_to_utf16();
 
     if (auto result = Core::TimeZone::set_current_time_zone(time_zone); result.is_error())
         return vm.throw_completion<JS::InternalError>(MUST(String::formatted("Could not set time zone: {}", result.error())));
 
     JS::clear_system_time_zone_cache();
-    return current_time_zone;
+    return current_time_zone_string;
 }
 
 TESTJS_GLOBAL_FUNCTION(to_utf8_bytes, toUTF8Bytes)
diff --git a/Tests/LibJS/test-primitive-string.cpp b/Tests/LibJS/test-primitive-string.cpp
index 250f157715..de3e939c16 100644
--- a/Tests/LibJS/test-primitive-string.cpp
+++ b/Tests/LibJS/test-primitive-string.cpp
@@ -35,14 +35,14 @@ struct TestVM {
 NEVER_INLINE static void materialize_temporary_rope(VM& vm)
 {
     auto rope = PrimitiveString::create(vm,
-        *PrimitiveString::create(vm, "hello"_string),
-        *PrimitiveString::create(vm, "world"_string));
+        *PrimitiveString::create(vm, "hello"_utf16),
+        *PrimitiveString::create(vm, "world"_utf16));
     EXPECT(rope->utf16_string_view() == "helloworld"sv);
 }
 
 NEVER_INLINE static void materialize_temporary_substring(VM& vm)
 {
-    auto source = PrimitiveString::create(vm, "foobar"_string);
+    auto source = PrimitiveString::create(vm, "foobar"_utf16);
     auto substring = PrimitiveString::create(vm, *source, 0, 3);
     EXPECT(substring->utf16_string_view() == "foo"sv);
 }
@@ -60,7 +60,7 @@ TEST_CASE(primitive_string_substring_supports_nested_ranges)
 {
     TestVM test_vm;
 
-    auto string = PrimitiveString::create(*test_vm.vm, "abcdef"_string);
+    auto string = PrimitiveString::create(*test_vm.vm, "abcdef"_utf16);
     auto substring = PrimitiveString::create(*test_vm.vm, *string, 1, 4);
     auto nested_substring = PrimitiveString::create(*test_vm.vm, *substring, 1, 2);
 
@@ -75,8 +75,8 @@ TEST_CASE(primitive_string_substring_materializes_rope_ranges)
     TestVM test_vm;
 
     auto rope = PrimitiveString::create(*test_vm.vm,
-        *PrimitiveString::create(*test_vm.vm, "abcd"_string),
-        *PrimitiveString::create(*test_vm.vm, "efgh"_string));
+        *PrimitiveString::create(*test_vm.vm, "abcd"_utf16),
+        *PrimitiveString::create(*test_vm.vm, "efgh"_utf16));
     auto substring = PrimitiveString::create(*test_vm.vm, *rope, 3, 3);
 
     EXPECT_EQ(substring->length_in_utf16_code_units(), 3u);
@@ -88,8 +88,8 @@ TEST_CASE(primitive_string_concat_short_flat_strings_creates_flat_string)
     TestVM test_vm;
 
     auto concatenated = PrimitiveString::create(*test_vm.vm,
-        *PrimitiveString::create(*test_vm.vm, "foo"_string),
-        *PrimitiveString::create(*test_vm.vm, "bar"_string));
+        *PrimitiveString::create(*test_vm.vm, "foo"_utf16),
+        *PrimitiveString::create(*test_vm.vm, "bar"_utf16));
 
     EXPECT(concatenated->has_utf16_string());
     EXPECT(concatenated->utf16_string_view() == "foobar"sv);
@@ -100,8 +100,8 @@ TEST_CASE(primitive_string_concat_longer_strings_stays_deferred)
     TestVM test_vm;
 
     auto concatenated = PrimitiveString::create(*test_vm.vm,
-        *PrimitiveString::create(*test_vm.vm, "abcd"_string),
-        *PrimitiveString::create(*test_vm.vm, "efgh"_string));
+        *PrimitiveString::create(*test_vm.vm, "abcd"_utf16),
+        *PrimitiveString::create(*test_vm.vm, "efgh"_utf16));
 
     EXPECT(!concatenated->has_utf16_string());
     EXPECT(concatenated->utf16_string_view() == "abcdefgh"sv);
@@ -111,8 +111,8 @@ TEST_CASE(primitive_string_substring_reuses_cached_single_ascii_strings)
 {
     TestVM test_vm;
 
-    auto cached_b = PrimitiveString::create(*test_vm.vm, "b"_string);
-    auto string = PrimitiveString::create(*test_vm.vm, "abcd"_string);
+    auto cached_b = PrimitiveString::create(*test_vm.vm, "b"_utf16);
+    auto string = PrimitiveString::create(*test_vm.vm, "abcd"_utf16);
     auto substring = PrimitiveString::create(*test_vm.vm, *string, 1, 1);
 
     EXPECT_EQ(substring.ptr(), cached_b.ptr());
@@ -122,7 +122,7 @@ TEST_CASE(primitive_string_substring_handles_surrogate_boundaries)
 {
     TestVM test_vm;
 
-    auto string = PrimitiveString::create(*test_vm.vm, "😀x"_string);
+    auto string = PrimitiveString::create(*test_vm.vm, "😀x"_utf16);
     auto leading_surrogate = PrimitiveString::create(*test_vm.vm, *string, 0, 1);
     auto trailing_surrogate = PrimitiveString::create(*test_vm.vm, *string, 1, 1);
     auto full_code_point = PrimitiveString::create(*test_vm.vm, *string, 0, 2);
@@ -138,7 +138,7 @@ TEST_CASE(primitive_string_concat_short_strings_handles_surrogate_boundaries)
 {
     TestVM test_vm;
 
-    auto string = PrimitiveString::create(*test_vm.vm, "😀"_string);
+    auto string = PrimitiveString::create(*test_vm.vm, "😀"_utf16);
     auto leading_surrogate = PrimitiveString::create(*test_vm.vm, *string, 0, 1);
     auto trailing_surrogate = PrimitiveString::create(*test_vm.vm, *string, 1, 1);
 
@@ -185,17 +185,17 @@ TEST_CASE(deferred_primitive_strings_do_not_evict_cached_strings)
 {
     TestVM test_vm;
 
-    auto cached_foo = PrimitiveString::create(*test_vm.vm, "foo"_string);
+    auto cached_foo = PrimitiveString::create(*test_vm.vm, "foo"_utf16);
 
     materialize_temporary_rope(*test_vm.vm);
     clobber_stack();
 
     test_vm.vm->heap().collect_garbage();
-    EXPECT_EQ(PrimitiveString::create(*test_vm.vm, "foo"_string).ptr(), cached_foo.ptr());
+    EXPECT_EQ(PrimitiveString::create(*test_vm.vm, "foo"_utf16).ptr(), cached_foo.ptr());
 
     materialize_temporary_substring(*test_vm.vm);
     clobber_stack();
 
     test_vm.vm->heap().collect_garbage();
-    EXPECT_EQ(PrimitiveString::create(*test_vm.vm, "foo"_string).ptr(), cached_foo.ptr());
+    EXPECT_EQ(PrimitiveString::create(*test_vm.vm, "foo"_utf16).ptr(), cached_foo.ptr());
 }
diff --git a/Tests/LibUnicode/TestDisplayNames.cpp b/Tests/LibUnicode/TestDisplayNames.cpp
index a1495df3ca..697d9c9cc6 100644
--- a/Tests/LibUnicode/TestDisplayNames.cpp
+++ b/Tests/LibUnicode/TestDisplayNames.cpp
@@ -11,72 +11,72 @@
 
 TEST_CASE(locale_mappings_en)
 {
-    auto language = Unicode::language_display_name("en"sv, "en"sv, Unicode::LanguageDisplay::Standard);
+    auto language = Unicode::language_display_name("en"sv, u"en"sv, Unicode::LanguageDisplay::Standard);
     EXPECT(language.has_value());
     EXPECT_EQ(*language, u"English"sv);
 
-    language = Unicode::language_display_name("en"sv, "i-definitely-don't-exist"sv, Unicode::LanguageDisplay::Standard);
+    language = Unicode::language_display_name("en"sv, u"i-definitely-don't-exist"sv, Unicode::LanguageDisplay::Standard);
     EXPECT(!language.has_value());
 
-    auto territory = Unicode::region_display_name("en"sv, "US"sv);
+    auto territory = Unicode::region_display_name("en"sv, u"US"sv);
     EXPECT(territory.has_value());
     EXPECT_EQ(*territory, u"United States"sv);
 
-    territory = Unicode::region_display_name("en"sv, "i-definitely-don't-exist"sv);
+    territory = Unicode::region_display_name("en"sv, u"i-definitely-don't-exist"sv);
     EXPECT(!territory.has_value());
 
-    auto script = Unicode::script_display_name("en"sv, "Latn"sv);
+    auto script = Unicode::script_display_name("en"sv, u"Latn"sv);
     EXPECT(script.has_value());
     EXPECT_EQ(*script, u"Latin"sv);
 
-    script = Unicode::script_display_name("en"sv, "i-definitely-don't-exist"sv);
+    script = Unicode::script_display_name("en"sv, u"i-definitely-don't-exist"sv);
     EXPECT(!script.has_value());
 }
 
 TEST_CASE(locale_mappings_fr)
 {
-    auto language = Unicode::language_display_name("fr"sv, "en"sv, Unicode::LanguageDisplay::Standard);
+    auto language = Unicode::language_display_name("fr"sv, u"en"sv, Unicode::LanguageDisplay::Standard);
     EXPECT(language.has_value());
     EXPECT_EQ(*language, u"anglais"sv);
 
-    language = Unicode::language_display_name("fr"sv, "i-definitely-don't-exist"sv, Unicode::LanguageDisplay::Standard);
+    language = Unicode::language_display_name("fr"sv, u"i-definitely-don't-exist"sv, Unicode::LanguageDisplay::Standard);
     EXPECT(!language.has_value());
 
-    auto territory = Unicode::region_display_name("fr"sv, "US"sv);
+    auto territory = Unicode::region_display_name("fr"sv, u"US"sv);
     EXPECT(territory.has_value());
     EXPECT_EQ(*territory, u"États-Unis"sv);
 
-    territory = Unicode::region_display_name("fr"sv, "i-definitely-don't-exist"sv);
+    territory = Unicode::region_display_name("fr"sv, u"i-definitely-don't-exist"sv);
     EXPECT(!territory.has_value());
 
-    auto script = Unicode::script_display_name("fr"sv, "Latn"sv);
+    auto script = Unicode::script_display_name("fr"sv, u"Latn"sv);
     EXPECT(script.has_value());
     EXPECT_EQ(*script, u"latin"sv);
 
-    script = Unicode::script_display_name("fr"sv, "i-definitely-don't-exist"sv);
+    script = Unicode::script_display_name("fr"sv, u"i-definitely-don't-exist"sv);
     EXPECT(!script.has_value());
 }
 
 TEST_CASE(locale_mappings_root)
 {
-    auto language = Unicode::language_display_name("und"sv, "en"sv, Unicode::LanguageDisplay::Standard);
+    auto language = Unicode::language_display_name("und"sv, u"en"sv, Unicode::LanguageDisplay::Standard);
     EXPECT(language.has_value());
     EXPECT_EQ(*language, u"en"sv);
 
-    language = Unicode::language_display_name("und"sv, "i-definitely-don't-exist"sv, Unicode::LanguageDisplay::Standard);
+    language = Unicode::language_display_name("und"sv, u"i-definitely-don't-exist"sv, Unicode::LanguageDisplay::Standard);
     EXPECT(!language.has_value());
 
-    auto territory = Unicode::region_display_name("und"sv, "US"sv);
+    auto territory = Unicode::region_display_name("und"sv, u"US"sv);
     EXPECT(territory.has_value());
     EXPECT_EQ(*territory, u"US"sv);
 
-    territory = Unicode::region_display_name("und"sv, "i-definitely-don't-exist"sv);
+    territory = Unicode::region_display_name("und"sv, u"i-definitely-don't-exist"sv);
     EXPECT(!territory.has_value());
 
-    auto script = Unicode::script_display_name("und"sv, "Latn"sv);
+    auto script = Unicode::script_display_name("und"sv, u"Latn"sv);
     EXPECT(script.has_value());
     EXPECT_EQ(*script, u"Latn"sv);
 
-    script = Unicode::script_display_name("und"sv, "i-definitely-don't-exist"sv);
+    script = Unicode::script_display_name("und"sv, u"i-definitely-don't-exist"sv);
     EXPECT(!script.has_value());
 }
diff --git a/Tests/LibUnicode/TestTimeZone.cpp b/Tests/LibUnicode/TestTimeZone.cpp
index c79a200124..556c2bf6a9 100644
--- a/Tests/LibUnicode/TestTimeZone.cpp
+++ b/Tests/LibUnicode/TestTimeZone.cpp
@@ -14,7 +14,8 @@ public:
     explicit TimeZoneGuard(StringView time_zone)
         : m_time_zone(Unicode::current_time_zone())
     {
-        (void)Unicode::set_current_time_zone(time_zone);
+        auto time_zone_utf16 = Utf16String::from_utf8(time_zone);
+        (void)Unicode::set_current_time_zone(time_zone_utf16);
     }
 
     ~TimeZoneGuard()
@@ -22,21 +23,21 @@ public:
         MUST(Unicode::set_current_time_zone(m_time_zone));
     }
 
-    String const& time_zone() const { return m_time_zone; }
+    Utf16String const& time_zone() const { return m_time_zone; }
 
 private:
-    String m_time_zone;
+    Utf16String m_time_zone;
 };
 
 TEST_CASE(current_time_zone)
 {
     {
         TimeZoneGuard guard { "America/New_York"sv };
-        EXPECT_EQ(Unicode::current_time_zone(), "America/New_York"sv);
+        EXPECT_EQ(Unicode::current_time_zone(), "America/New_York"_utf16);
     }
     {
         TimeZoneGuard guard { "America/Los_Angeles"sv };
-        EXPECT_EQ(Unicode::current_time_zone(), "America/Los_Angeles"sv);
+        EXPECT_EQ(Unicode::current_time_zone(), "America/Los_Angeles"_utf16);
     }
     {
         TimeZoneGuard guard { "ladybird"sv };
@@ -47,34 +48,35 @@ TEST_CASE(current_time_zone)
 TEST_CASE(available_time_zones)
 {
     auto const& time_zones = Unicode::available_time_zones();
-    EXPECT(time_zones.contains_slow("UTC"sv));
-    EXPECT(!time_zones.contains_slow("EAT"sv));
+    EXPECT(time_zones.contains_slow("UTC"_utf16));
+    EXPECT(!time_zones.contains_slow("EAT"_utf16));
 }
 
 TEST_CASE(available_time_zones_in_region)
 {
     {
         auto time_zones = Unicode::available_time_zones_in_region("AD"sv);
-        EXPECT_EQ(time_zones, to_array({ "Europe/Andorra"_string }));
+        EXPECT_EQ(time_zones, to_array({ "Europe/Andorra"_utf16 }));
     }
     {
         auto time_zones = Unicode::available_time_zones_in_region("ES"sv);
-        EXPECT_EQ(time_zones, to_array({ "Africa/Ceuta"_string, "Atlantic/Canary"_string, "Europe/Madrid"_string }));
+        EXPECT_EQ(time_zones, to_array({ "Africa/Ceuta"_utf16, "Atlantic/Canary"_utf16, "Europe/Madrid"_utf16 }));
     }
 }
 
 TEST_CASE(resolve_primary_time_zone)
 {
-    EXPECT_EQ(Unicode::resolve_primary_time_zone("UTC"sv), "Etc/UTC"sv);
-    EXPECT_EQ(Unicode::resolve_primary_time_zone("Asia/Katmandu"sv), "Asia/Kathmandu"sv);
-    EXPECT_EQ(Unicode::resolve_primary_time_zone("Australia/Canberra"sv), "Australia/Sydney"sv);
+    EXPECT_EQ(Unicode::resolve_primary_time_zone("UTC"sv), "Etc/UTC"_utf16);
+    EXPECT_EQ(Unicode::resolve_primary_time_zone("Asia/Katmandu"sv), "Asia/Kathmandu"_utf16);
+    EXPECT_EQ(Unicode::resolve_primary_time_zone("Australia/Canberra"sv), "Australia/Sydney"_utf16);
 }
 
 using enum Unicode::TimeZoneOffset::InDST;
 
 static void test_offset(StringView time_zone, i64 time, AK::Duration expected_offset, Unicode::TimeZoneOffset::InDST expected_in_dst)
 {
-    auto actual_offset = Unicode::time_zone_offset(time_zone, AK::UnixDateTime::from_seconds_since_epoch(time));
+    auto time_zone_utf16 = Utf16String::from_utf8(time_zone);
+    auto actual_offset = Unicode::time_zone_offset(time_zone_utf16, AK::UnixDateTime::from_seconds_since_epoch(time));
     VERIFY(actual_offset.has_value());
 
     EXPECT_EQ(actual_offset->offset, expected_offset);
@@ -86,6 +88,22 @@ static constexpr AK::Duration offset(i64 sign, i64 hours, i64 minutes, i64 secon
     return AK::Duration::from_seconds(sign * ((hours * 3600) + (minutes * 60) + seconds));
 }
 
+TEST_CASE(time_zone_ids_with_utf16_storage)
+{
+    char16_t const region[] = u"DE";
+    auto time_zones = Unicode::available_time_zones_in_region({ region, 2 });
+    EXPECT(time_zones.contains_slow("Europe/Berlin"_utf16));
+
+    char16_t const time_zone[] = u"Europe/Berlin";
+    auto time_zone_view = Utf16View { time_zone, 13 };
+    EXPECT_EQ(Unicode::resolve_primary_time_zone(time_zone_view), "Europe/Berlin"_utf16);
+
+    auto actual_offset = Unicode::time_zone_offset(time_zone_view, AK::UnixDateTime::from_seconds_since_epoch(0));
+    VERIFY(actual_offset.has_value());
+    EXPECT_EQ(actual_offset->offset, offset(+1, 1, 0, 0));
+    EXPECT_EQ(actual_offset->in_dst, No);
+}
+
 // Useful website to convert times in the TZDB (which sometimes are and aren't UTC) to UTC and the desired local time:
 // https://www.epochconverter.com/#tools
 //
diff --git a/Tests/LibWasm/test-wasm.cpp b/Tests/LibWasm/test-wasm.cpp
index 8c2a297db4..d15e3f5b70 100644
--- a/Tests/LibWasm/test-wasm.cpp
+++ b/Tests/LibWasm/test-wasm.cpp
@@ -26,17 +26,17 @@ TESTJS_GLOBAL_FUNCTION(read_binary_wasm_file, readBinaryWasmFile)
     auto filename = TRY(vm.argument(0).to_utf16_string(vm)).to_utf8_but_should_be_ported_to_utf16();
     auto file = Core::File::open(filename, Core::File::OpenMode::Read);
     if (file.is_error())
-        return vm.throw_completion<JS::TypeError>(error_code_to_string(file.error().code()));
+        return vm.throw_completion<JS::TypeError>(Utf16String::from_utf8(error_code_to_string(file.error().code())));
 
     auto file_size = file.value()->size();
     if (file_size.is_error())
-        return vm.throw_completion<JS::TypeError>(error_code_to_string(file_size.error().code()));
+        return vm.throw_completion<JS::TypeError>(Utf16String::from_utf8(error_code_to_string(file_size.error().code())));
 
     auto array = TRY(JS::Uint8Array::create(realm, file_size.value()));
 
     auto read = file.value()->read_until_filled(array->data());
     if (read.is_error())
-        return vm.throw_completion<JS::TypeError>(error_code_to_string(read.error().code()));
+        return vm.throw_completion<JS::TypeError>(Utf16String::from_utf8(error_code_to_string(read.error().code())));
 
     return JS::Value(array);
 }
@@ -66,10 +66,10 @@ public:
         linker.link(spec_test_namespace());
         auto link_result = linker.finish();
         if (link_result.is_error())
-            return vm.throw_completion<JS::TypeError>("Link failed"sv);
+            return vm.throw_completion<JS::TypeError>("Link failed"_utf16);
         auto result = machine().instantiate(*instance->m_module, link_result.release_value());
         if (result.is_error())
-            return vm.throw_completion<JS::TypeError>(result.release_error().error);
+            return vm.throw_completion<JS::TypeError>(Utf16String::from_utf8(result.release_error().error));
         instance->m_module_instance = result.release_value();
         return instance.ptr();
     }
@@ -169,12 +169,12 @@ TESTJS_GLOBAL_FUNCTION(parse_webassembly_module, parseWebAssemblyModule)
     auto& realm = *vm.current_realm();
     auto object = TRY(vm.argument(0).to_object(vm));
     if (!is<JS::Uint8Array>(*object))
-        return vm.throw_completion<JS::TypeError>("Expected a Uint8Array argument to parse_webassembly_module"sv);
+        return vm.throw_completion<JS::TypeError>("Expected a Uint8Array argument to parse_webassembly_module"_utf16);
     auto& array = static_cast<JS::Uint8Array&>(*object);
     FixedMemoryStream stream { array.data() };
     auto result = Wasm::Module::parse(stream);
     if (result.is_error())
-        return vm.throw_completion<JS::SyntaxError>(Wasm::parse_error_to_byte_string(result.error()));
+        return vm.throw_completion<JS::SyntaxError>(Utf16String::from_utf8(Wasm::parse_error_to_byte_string(result.error())));
 
     HashMap<Wasm::Linker::Name, Wasm::ExternValue> imports;
     auto import_value = vm.argument(1);
@@ -197,14 +197,14 @@ TESTJS_GLOBAL_FUNCTION(validate_webassembly_module, validateWebAssemblyModule)
 {
     auto object = TRY(vm.argument(0).to_object(vm));
     if (!is<JS::Uint8Array>(*object))
-        return vm.throw_completion<JS::TypeError>("Expected a Uint8Array argument to validate_webassembly_module"sv);
+        return vm.throw_completion<JS::TypeError>("Expected a Uint8Array argument to validate_webassembly_module"_utf16);
     auto& array = static_cast<JS::Uint8Array&>(*object);
     FixedMemoryStream stream { array.data() };
     auto result = Wasm::Module::parse(stream);
     if (result.is_error())
-        return vm.throw_completion<JS::SyntaxError>(Wasm::parse_error_to_byte_string(result.error()));
+        return vm.throw_completion<JS::SyntaxError>(Utf16String::from_utf8(Wasm::parse_error_to_byte_string(result.error())));
     if (auto validation = WebAssemblyModule::machine().validate(*result.value(), {}, Wasm::CompileToNative::No); validation.is_error())
-        return vm.throw_completion<JS::SyntaxError>(validation.release_error().error_string);
+        return vm.throw_completion<JS::SyntaxError>(Utf16String::from_utf8(validation.release_error().error_string));
     return JS::js_undefined();
 }
 
@@ -212,11 +212,11 @@ TESTJS_GLOBAL_FUNCTION(compare_typed_arrays, compareTypedArrays)
 {
     auto lhs = TRY(vm.argument(0).to_object(vm));
     if (!is<JS::TypedArrayBase>(*lhs))
-        return vm.throw_completion<JS::TypeError>("Expected a TypedArray"sv);
+        return vm.throw_completion<JS::TypeError>("Expected a TypedArray"_utf16);
     auto& lhs_array = static_cast<JS::TypedArrayBase&>(*lhs);
     auto rhs = TRY(vm.argument(1).to_object(vm));
     if (!is<JS::TypedArrayBase>(*rhs))
-        return vm.throw_completion<JS::TypeError>("Expected a TypedArray"sv);
+        return vm.throw_completion<JS::TypeError>("Expected a TypedArray"_utf16);
     auto& rhs_array = static_cast<JS::TypedArrayBase&>(*rhs);
     auto lhs_record = JS::make_typed_array_with_buffer_witness_record(lhs_array, JS::ArrayBuffer::Order::SeqCst);
     auto rhs_record = JS::make_typed_array_with_buffer_witness_record(rhs_array, JS::ArrayBuffer::Order::SeqCst);
@@ -266,7 +266,7 @@ TESTJS_GLOBAL_FUNCTION(is_valid_funcref_in, isValidFuncrefIn)
     auto value = TRY(vm.argument(0).to_index(vm));
     auto module_object = TRY(vm.argument(1).to_object(vm));
     if (!is<WebAssemblyModule>(*module_object))
-        return vm.throw_completion<JS::TypeError>("Expected a WebAssemblyModule"sv);
+        return vm.throw_completion<JS::TypeError>("Expected a WebAssemblyModule"_utf16);
     auto& module = static_cast<WebAssemblyModule&>(*module_object);
     return JS::Value(module.machine().store().get(Wasm::FunctionAddress { value }) != nullptr);
 }
@@ -275,11 +275,11 @@ TESTJS_GLOBAL_FUNCTION(test_simd_vector, testSIMDVector)
 {
     auto expected = TRY(vm.argument(0).to_object(vm));
     if (!is<JS::Array>(*expected))
-        return vm.throw_completion<JS::TypeError>("Expected an Array"sv);
+        return vm.throw_completion<JS::TypeError>("Expected an Array"_utf16);
     auto& expected_array = static_cast<JS::Array&>(*expected);
     auto got = TRY(vm.argument(1).to_object(vm));
     if (!is<JS::TypedArrayBase>(*got))
-        return vm.throw_completion<JS::TypeError>("Expected a TypedArray"sv);
+        return vm.throw_completion<JS::TypeError>("Expected a TypedArray"_utf16);
     auto& got_array = static_cast<JS::TypedArrayBase&>(*got);
     auto element_size = 128 / TRY(TRY(expected_array.get("length"_utf16_fly_string)).to_u32(vm));
     size_t i = 0;
@@ -291,7 +291,7 @@ TESTJS_GLOBAL_FUNCTION(test_simd_vector, testSIMDVector)
         auto expect = TRY(expected_array.get(it_index));
         if (expect.is_string()) {
             if (element_size != 32 && element_size != 64)
-                return vm.throw_completion<JS::TypeError>("Expected element of size 32 or 64"sv);
+                return vm.throw_completion<JS::TypeError>("Expected element of size 32 or 64"_utf16);
             auto string = expect.as_string().utf16_string_view().to_utf8_but_should_be_ported_to_utf16();
             if (string == "nan:canonical") {
                 auto is_canonical = element_size == 32 ? _is_canonical_nan32(got) : _is_canonical_nan64(got);
@@ -305,7 +305,7 @@ TESTJS_GLOBAL_FUNCTION(test_simd_vector, testSIMDVector)
                     return false;
                 continue;
             }
-            return vm.throw_completion<JS::TypeError>(ByteString::formatted("Bad SIMD float expectation: {}", string));
+            return vm.throw_completion<JS::TypeError>(Utf16String::formatted("Bad SIMD float expectation: {}", string));
         }
         u64 expect_value = expect.is_bigint() ? TRY(expect.to_bigint_uint64(vm)) : (u64)TRY(expect.to_index(vm));
         if (got != expect_value)
@@ -327,7 +327,7 @@ JS_DEFINE_NATIVE_FUNCTION(WebAssemblyModule::get_export)
     auto this_value = vm.this_value();
     auto object = TRY(this_value.to_object(vm));
     if (!is<WebAssemblyModule>(*object))
-        return vm.throw_completion<JS::TypeError>("Not a WebAssemblyModule"sv);
+        return vm.throw_completion<JS::TypeError>("Not a WebAssemblyModule"_utf16);
     auto& instance = static_cast<WebAssemblyModule&>(*object);
     for (auto& entry : instance.module_instance().exports()) {
         if (entry.name() == name.to_byte_string()) {
@@ -372,13 +372,13 @@ JS_DEFINE_NATIVE_FUNCTION(WebAssemblyModule::get_export)
                 }
                 case Wasm::ValueType::I8:
                 case Wasm::ValueType::I16:
-                    return vm.throw_completion<JS::TypeError>("Unsupported heap reference"sv);
+                    return vm.throw_completion<JS::TypeError>("Unsupported heap reference"_utf16);
                 }
             }
-            return vm.throw_completion<JS::TypeError>(TRY_OR_THROW_OOM(vm, String::formatted("'{}' does not refer to a function or a global", name)));
+            return vm.throw_completion<JS::TypeError>(Utf16String::formatted("'{}' does not refer to a function or a global", name));
         }
     }
-    return vm.throw_completion<JS::TypeError>(TRY_OR_THROW_OOM(vm, String::formatted("'{}' could not be found", name)));
+    return vm.throw_completion<JS::TypeError>(Utf16String::formatted("'{}' could not be found", name));
 }
 
 JS_DEFINE_NATIVE_FUNCTION(WebAssemblyModule::wasm_invoke)
@@ -387,16 +387,16 @@ JS_DEFINE_NATIVE_FUNCTION(WebAssemblyModule::wasm_invoke)
     Wasm::FunctionAddress function_address { address };
     auto function_instance = WebAssemblyModule::machine().store().get(function_address);
     if (!function_instance)
-        return vm.throw_completion<JS::TypeError>("Invalid function address"sv);
+        return vm.throw_completion<JS::TypeError>("Invalid function address"_utf16);
 
     Wasm::FunctionType const* type { nullptr };
     function_instance->visit([&](auto& value) { type = &value.type(); });
     if (!type)
-        return vm.throw_completion<JS::TypeError>("Invalid function found at given address"sv);
+        return vm.throw_completion<JS::TypeError>("Invalid function found at given address"_utf16);
 
     Vector<Wasm::Value> arguments;
     if (type->parameters().size() + 1 > vm.argument_count())
-        return vm.throw_completion<JS::TypeError>(TRY_OR_THROW_OOM(vm, String::formatted("Expected {} arguments for call, but found {}", type->parameters().size() + 1, vm.argument_count())));
+        return vm.throw_completion<JS::TypeError>(Utf16String::formatted("Expected {} arguments for call, but found {}", type->parameters().size() + 1, vm.argument_count()));
     size_t index = 1;
     for (auto& param : type->parameters()) {
         auto argument = vm.argument(index++);
@@ -429,7 +429,7 @@ JS_DEFINE_NATIVE_FUNCTION(WebAssemblyModule::wasm_invoke)
         case Wasm::ValueType::Kind::V128: {
             auto object = MUST(argument.to_object(vm));
             if (!is<JS::TypedArrayBase>(*object))
-                return vm.throw_completion<JS::TypeError>("Expected typed array"sv);
+                return vm.throw_completion<JS::TypeError>("Expected typed array"_utf16);
             auto& array = static_cast<JS::TypedArrayBase&>(*object);
             u128 bits = 0;
             auto* ptr = bit_cast<u8*>(&bits);
@@ -457,13 +457,13 @@ JS_DEFINE_NATIVE_FUNCTION(WebAssemblyModule::wasm_invoke)
             if (argument.is_null())
                 arguments.append(Wasm::Value(Wasm::Reference { Wasm::Reference::Null { Wasm::ValueType(Wasm::ValueType::Kind::ExceptionReference) } }));
             else
-                return vm.throw_completion<JS::TypeError>("Exception references are not supported"sv);
+                return vm.throw_completion<JS::TypeError>("Exception references are not supported"_utf16);
             break;
         case Wasm::ValueType::Kind::TypeUseReference:
             if (argument.is_null())
                 arguments.append(Wasm::Value(Wasm::Reference { Wasm::Reference::Null { Wasm::ValueType(Wasm::ValueType::Kind::TypeUseReference, param.unsafe_typeindex()) } }));
             else
-                return vm.throw_completion<JS::TypeError>("GC Heap references are not supported"sv);
+                return vm.throw_completion<JS::TypeError>("GC Heap references are not supported"_utf16);
             break;
         case Wasm::ValueType::Kind::AnyReference:
             if (argument.is_null()) {
@@ -484,11 +484,11 @@ JS_DEFINE_NATIVE_FUNCTION(WebAssemblyModule::wasm_invoke)
             if (argument.is_null())
                 arguments.append(Wasm::Value(Wasm::Reference { Wasm::Reference::Null { Wasm::ValueType(param.kind()) } }));
             else
-                return vm.throw_completion<JS::TypeError>("GC Heap references are not supported"sv);
+                return vm.throw_completion<JS::TypeError>("GC Heap references are not supported"_utf16);
             break;
         case Wasm::ValueType::Kind::I8:
         case Wasm::ValueType::Kind::I16:
-            return vm.throw_completion<JS::TypeError>("Packed types are not valid parameter types"sv);
+            return vm.throw_completion<JS::TypeError>("Packed types are not valid parameter types"_utf16);
         }
     }
 
@@ -497,7 +497,7 @@ JS_DEFINE_NATIVE_FUNCTION(WebAssemblyModule::wasm_invoke)
     if (result.is_trap()) {
         if (auto ptr = result.trap().data.get_pointer<Wasm::ExternallyManagedTrap>())
             return ptr->unsafe_external_object_as<JS::Completion>();
-        return vm.throw_completion<JS::TypeError>(TRY_OR_THROW_OOM(vm, String::formatted("Execution trapped: {}", result.trap().format())));
+        return vm.throw_completion<JS::TypeError>(Utf16String::formatted("Execution trapped: {}", result.trap().format()));
     }
 
     if (result.values().is_empty())
@@ -537,7 +537,7 @@ JS_DEFINE_NATIVE_FUNCTION(WebAssemblyModule::wasm_invoke)
             return JS::js_null();
         case Wasm::ValueType::I8:
         case Wasm::ValueType::I16:
-            return vm.throw_completion<JS::TypeError>("Unsupported packed type"sv);
+            return vm.throw_completion<JS::TypeError>("Unsupported packed type"_utf16);
         }
         VERIFY_NOT_REACHED();
     };
diff --git a/Tests/LibWeb/Text/expected/Crypto/SubtleCrypto-jwk-non-ascii-base64url.txt b/Tests/LibWeb/Text/expected/Crypto/SubtleCrypto-jwk-non-ascii-base64url.txt
new file mode 100644
index 0000000000..a3a68b8008
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/Crypto/SubtleCrypto-jwk-non-ascii-base64url.txt
@@ -0,0 +1 @@
+DataError
diff --git a/Tests/LibWeb/Text/input/Crypto/SubtleCrypto-jwk-non-ascii-base64url.html b/Tests/LibWeb/Text/input/Crypto/SubtleCrypto-jwk-non-ascii-base64url.html
new file mode 100644
index 0000000000..cad4078290
--- /dev/null
+++ b/Tests/LibWeb/Text/input/Crypto/SubtleCrypto-jwk-non-ascii-base64url.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<script src="../include.js"></script>
+<script>
+    asyncTest(async done => {
+        const jwk = { alg: "A128GCM", kty: "oct", k: "é" };
+
+        try {
+            await crypto.subtle.importKey("jwk", jwk, "AES-GCM", false, [ "encrypt" ]);
+            println("FAIL: import succeeded");
+        } catch (error) {
+            println(error.name);
+        }
+
+        done();
+    });
+</script>
diff --git a/Utilities/js.cpp b/Utilities/js.cpp
index ff16db731c..10ac55356b 100644
--- a/Utilities/js.cpp
+++ b/Utilities/js.cpp
@@ -111,7 +111,7 @@ static int s_exit_code = 0;
 
 static ErrorOr<void> print_inline(JS::Value value, Stream& stream)
 {
-    JS::PrintContext print_context { .vm = *g_vm, .stream = stream, .strip_ansi = s_strip_ansi, .raw_strings = s_raw_strings };
+    JS::PrintContext print_context { .vm = *g_vm, .stream = &stream, .strip_ansi = s_strip_ansi, .raw_strings = s_raw_strings };
     return JS::print(value, print_context);
 }
 
@@ -209,7 +209,7 @@ static ErrorOr<bool> parse_and_run(JS::Realm& realm, StringView source, StringVi
             if (!hint.is_empty())
                 outln("{}", hint);
 
-            auto error_string = error.to_string();
+            auto error_string = error.to_utf16_string();
             outln("{}", error_string);
             result = vm.throw_completion<JS::SyntaxError>(move(error_string));
         } else {
@@ -228,7 +228,7 @@ static ErrorOr<bool> parse_and_run(JS::Realm& realm, StringView source, StringVi
             if (!hint.is_empty())
                 outln("{}", hint);
 
-            auto error_string = error.to_string();
+            auto error_string = error.to_utf16_string();
             outln("{}", error_string);
             result = vm.throw_completion<JS::SyntaxError>(move(error_string));
         } else {
@@ -266,7 +266,7 @@ static JS::ThrowCompletionOr<JS::Value> load_ini_impl(JS::VM& vm)
 {
     auto& realm = *vm.current_realm();
 
-    auto filename = TRY(vm.argument(0).to_byte_string(vm));
+    auto filename = TRY(vm.argument(0).to_utf16_string(vm)).to_utf8_but_should_be_ported_to_utf16().to_byte_string();
     auto file_or_error = Core::File::open(filename, Core::File::OpenMode::Read);
     if (file_or_error.is_error())
         return vm.throw_completion<JS::Error>(TRY_OR_THROW_OOM(vm, String::formatted("Failed to open '{}': {}", filename, file_or_error.error())));
@@ -277,7 +277,7 @@ static JS::ThrowCompletionOr<JS::Value> load_ini_impl(JS::VM& vm)
         auto group_object = JS::Object::create(realm, realm.intrinsics().object_prototype());
         for (auto const& key : config_file->keys(group)) {
             auto entry = config_file->read_entry(group, key);
-            group_object->define_direct_property(Utf16String::from_utf8(key), JS::PrimitiveString::create(vm, move(entry)), JS::Attribute::Enumerable | JS::Attribute::Configurable | JS::Attribute::Writable);
+            group_object->define_direct_property(Utf16String::from_utf8(key), JS::PrimitiveString::create(vm, Utf16String::from_utf8(entry)), JS::Attribute::Enumerable | JS::Attribute::Configurable | JS::Attribute::Writable);
         }
         object->define_direct_property(Utf16String::from_utf8(group), group_object, JS::Attribute::Enumerable | JS::Attribute::Configurable | JS::Attribute::Writable);
     }