LibJS: Port Intl locale resolution to String

20 files changed, 207 insertions, 204 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/Intl/AbstractOperations.cpp b/Userland/Libraries/LibJS/Runtime/Intl/AbstractOperations.cpp
index fbc8816be1..f600d3ba0c 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/AbstractOperations.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Intl/AbstractOperations.cpp
@@ -80,7 +80,7 @@ ThrowCompletionOr<Optional<::Locale::LocaleID>> is_structurally_valid_language_t
 }
 
 // 6.2.3 CanonicalizeUnicodeLocaleId ( locale ), https://tc39.es/ecma402/#sec-canonicalizeunicodelocaleid
-ThrowCompletionOr<DeprecatedString> canonicalize_unicode_locale_id(VM& vm, ::Locale::LocaleID& locale)
+ThrowCompletionOr<String> canonicalize_unicode_locale_id(VM& vm, ::Locale::LocaleID& locale)
 {
     // Note: This implementation differs from the spec in how Step 3 is implemented. The spec assumes
     // the input to this method is a string, and is written such that operations are performed on parts
@@ -118,7 +118,7 @@ ThrowCompletionOr<DeprecatedString> canonicalize_unicode_locale_id(VM& vm, ::Loc
     VERIFY(locale_id.has_value());
 
     // 4. Return localeId.
-    return locale_id->to_deprecated_string();
+    return locale_id.release_value();
 }
 
 // 6.3.1 IsWellFormedCurrencyCode ( currency ), https://tc39.es/ecma402/#sec-iswellformedcurrencycode
@@ -183,18 +183,18 @@ bool is_well_formed_unit_identifier(StringView unit_identifier)
 }
 
 // 9.2.1 CanonicalizeLocaleList ( locales ), https://tc39.es/ecma402/#sec-canonicalizelocalelist
-ThrowCompletionOr<Vector<DeprecatedString>> canonicalize_locale_list(VM& vm, Value locales)
+ThrowCompletionOr<Vector<String>> 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<DeprecatedString> {};
+        return Vector<String> {};
     }
 
     // 2. Let seen be a new empty List.
-    Vector<DeprecatedString> seen;
+    Vector<String> seen;
 
     Object* object = nullptr;
     // 3. If Type(locales) is String or Type(locales) is Object and locales has an [[InitializedLocale]] internal slot, then
@@ -228,9 +228,9 @@ ThrowCompletionOr<Vector<DeprecatedString>> canonicalize_locale_list(VM& vm, Val
 
             // ii. If Type(kValue) is not String or Object, throw a TypeError exception.
             if (!key_value.is_string() && !key_value.is_object())
-                return vm.throw_completion<TypeError>(ErrorType::NotAnObjectOrString, key_value.to_string_without_side_effects());
+                return vm.throw_completion<TypeError>(ErrorType::NotAnObjectOrString, key_value);
 
-            DeprecatedString tag;
+            String tag;
 
             // iii. If Type(kValue) is Object and kValue has an [[InitializedLocale]] internal slot, then
             if (key_value.is_object() && is<Locale>(key_value.as_object())) {
@@ -240,7 +240,7 @@ ThrowCompletionOr<Vector<DeprecatedString>> canonicalize_locale_list(VM& vm, Val
             // iv. Else,
             else {
                 // 1. Let tag be ? ToString(kValue).
-                tag = TRY(key_value.to_deprecated_string(vm));
+                tag = TRY(key_value.to_string(vm));
             }
 
             // v. If ! IsStructurallyValidLanguageTag(tag) is false, throw a RangeError exception.
@@ -264,7 +264,7 @@ ThrowCompletionOr<Vector<DeprecatedString>> canonicalize_locale_list(VM& vm, Val
 }
 
 // 9.2.2 BestAvailableLocale ( availableLocales, locale ), https://tc39.es/ecma402/#sec-bestavailablelocale
-Optional<DeprecatedString> best_available_locale(StringView locale)
+Optional<StringView> best_available_locale(StringView locale)
 {
     // 1. Let candidate be locale.
     StringView candidate = locale;
@@ -290,12 +290,12 @@ Optional<DeprecatedString> best_available_locale(StringView locale)
 }
 
 struct MatcherResult {
-    DeprecatedString locale;
+    String locale;
     Vector<::Locale::Extension> extensions {};
 };
 
 // 9.2.3 LookupMatcher ( availableLocales, requestedLocales ), https://tc39.es/ecma402/#sec-lookupmatcher
-static ThrowCompletionOr<MatcherResult> lookup_matcher(VM& vm, Vector<DeprecatedString> const& requested_locales)
+static ThrowCompletionOr<MatcherResult> lookup_matcher(VM& vm, Vector<String> const& requested_locales)
 {
     // 1. Let result be a new Record.
     MatcherResult result {};
@@ -307,7 +307,7 @@ static ThrowCompletionOr<MatcherResult> lookup_matcher(VM& vm, Vector<Deprecated
 
         // a. Let noExtensionsLocale be the String value that is locale with any Unicode locale extension sequences removed.
         auto extensions = locale_id->remove_extension_type<::Locale::LocaleExtension>();
-        auto no_extensions_locale = locale_id->to_deprecated_string();
+        auto no_extensions_locale = TRY_OR_THROW_OOM(vm, locale_id->to_string());
 
         // b. Let availableLocale be ! BestAvailableLocale(availableLocales, noExtensionsLocale).
         auto available_locale = best_available_locale(no_extensions_locale);
@@ -315,7 +315,7 @@ static ThrowCompletionOr<MatcherResult> lookup_matcher(VM& vm, Vector<Deprecated
         // c. If availableLocale is not undefined, then
         if (available_locale.has_value()) {
             // i. Set result.[[locale]] to availableLocale.
-            result.locale = available_locale.release_value();
+            result.locale = TRY_OR_THROW_OOM(vm, String::from_utf8(*available_locale));
 
             // ii. If locale and noExtensionsLocale are not the same String value, then
             if (locale != no_extensions_locale) {
@@ -331,14 +331,14 @@ static ThrowCompletionOr<MatcherResult> lookup_matcher(VM& vm, Vector<Deprecated
 
     // 3. Let defLocale be ! DefaultLocale().
     // 4. Set result.[[locale]] to defLocale.
-    result.locale = ::Locale::default_locale();
+    result.locale = TRY_OR_THROW_OOM(vm, String::from_utf8(::Locale::default_locale()));
 
     // 5. Return result.
     return result;
 }
 
 // 9.2.4 BestFitMatcher ( availableLocales, requestedLocales ), https://tc39.es/ecma402/#sec-bestfitmatcher
-static ThrowCompletionOr<MatcherResult> best_fit_matcher(VM& vm, Vector<DeprecatedString> const& requested_locales)
+static ThrowCompletionOr<MatcherResult> best_fit_matcher(VM& vm, Vector<String> const& requested_locales)
 {
     // The algorithm is implementation dependent, but should produce results that a typical user of the requested locales would
     // perceive as at least as good as those produced by the LookupMatcher abstract operation.
@@ -346,14 +346,14 @@ static ThrowCompletionOr<MatcherResult> best_fit_matcher(VM& vm, Vector<Deprecat
 }
 
 // 9.2.6 InsertUnicodeExtensionAndCanonicalize ( locale, extension ), https://tc39.es/ecma402/#sec-insert-unicode-extension-and-canonicalize
-ThrowCompletionOr<DeprecatedString> insert_unicode_extension_and_canonicalize(VM& vm, ::Locale::LocaleID locale, ::Locale::LocaleExtension extension)
+ThrowCompletionOr<String> insert_unicode_extension_and_canonicalize(VM& vm, ::Locale::LocaleID locale, ::Locale::LocaleExtension extension)
 {
     // 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
     // of that string. LibUnicode gives us the parsed locale in a structure, so we can mutate that
     // structure directly.
     TRY_OR_THROW_OOM(vm, locale.extensions.try_append(move(extension)));
-    return TRY(canonicalize_unicode_locale_id(vm, locale));
+    return canonicalize_unicode_locale_id(vm, locale);
 }
 
 template<typename T>
@@ -377,7 +377,7 @@ static auto& find_key_in_value(T& value, StringView key)
 }
 
 // 9.2.7 ResolveLocale ( availableLocales, requestedLocales, options, relevantExtensionKeys, localeData ), https://tc39.es/ecma402/#sec-resolvelocale
-ThrowCompletionOr<LocaleResult> resolve_locale(VM& vm, Vector<DeprecatedString> const& requested_locales, LocaleOptions const& options, Span<StringView const> relevant_extension_keys)
+ThrowCompletionOr<LocaleResult> resolve_locale(VM& vm, Vector<String> const& requested_locales, LocaleOptions const& options, Span<StringView const> relevant_extension_keys)
 {
     // 1. Let matcher be options.[[localeMatcher]].
     auto const& matcher = options.locale_matcher;
@@ -434,9 +434,9 @@ ThrowCompletionOr<LocaleResult> resolve_locale(VM& vm, Vector<DeprecatedString>
         // f. Assert: Type(value) is either String or Null.
         // NOTE: ECMA-402 assumes keyLocaleData is sorted by locale preference. Our list is sorted
         //       alphabetically, so we get the locale's preferred value from LibUnicode.
-        Optional<DeprecatedString> value;
+        Optional<String> value;
         if (auto preference = ::Locale::get_preferred_keyword_value_for_locale(found_locale, key); preference.has_value())
-            value = *preference;
+            value = TRY_OR_THROW_OOM(vm, String::from_utf8(*preference));
 
         // g. Let supportedExtensionAddition be "".
         Optional<::Locale::Keyword> supported_extension_addition {};
@@ -456,7 +456,7 @@ ThrowCompletionOr<LocaleResult> resolve_locale(VM& vm, Vector<DeprecatedString>
                 // a. If keyLocaleData contains requestedValue, then
                 if (key_locale_data.contains_slow(requested_value)) {
                     // i. Let value be requestedValue.
-                    value = requested_value.to_deprecated_string();
+                    value = move(requested_value);
 
                     // ii. Let supportedExtensionAddition be the string-concatenation of "-", key, "-", and value.
                     supported_extension_addition = ::Locale::Keyword { TRY_OR_THROW_OOM(vm, String::from_utf8(key)), move(entry.value) };
@@ -465,7 +465,7 @@ ThrowCompletionOr<LocaleResult> resolve_locale(VM& vm, Vector<DeprecatedString>
             // 4. Else if keyLocaleData contains "true", then
             else if (key_locale_data.contains_slow("true"sv)) {
                 // a. Let value be "true".
-                value = "true"sv;
+                value = TRY_OR_THROW_OOM(vm, String::from_utf8("true"sv));
 
                 // b. Let supportedExtensionAddition be the string-concatenation of "-" and key.
                 supported_extension_addition = ::Locale::Keyword { TRY_OR_THROW_OOM(vm, String::from_utf8(key)), {} };
@@ -483,14 +483,12 @@ ThrowCompletionOr<LocaleResult> resolve_locale(VM& vm, Vector<DeprecatedString>
         if (options_value.has_value()) {
             // 1. Let optionsValue be the string optionsValue after performing the algorithm steps to transform Unicode extension values to canonical syntax per Unicode Technical Standard #35 LDML § 3.2.1 Canonical Unicode Locale Identifiers, treating key as ukey and optionsValue as uvalue productions.
             // 2. Let optionsValue be the string optionsValue after performing the algorithm steps to replace Unicode extension values with their canonical form per Unicode Technical Standard #35 LDML § 3.2.1 Canonical Unicode Locale Identifiers, treating key as ukey and optionsValue as uvalue productions.
-            auto options_value_string = TRY_OR_THROW_OOM(vm, String::from_deprecated_string(*options_value));
-            TRY_OR_THROW_OOM(vm, ::Locale::canonicalize_unicode_extension_values(key, options_value_string, true));
-            options_value = options_value_string.to_deprecated_string();
+            TRY_OR_THROW_OOM(vm, ::Locale::canonicalize_unicode_extension_values(key, *options_value, true));
 
             // 3. If optionsValue is the empty String, then
             if (options_value->is_empty()) {
                 // a. Let optionsValue be "true".
-                options_value = "true"sv;
+                options_value = TRY_OR_THROW_OOM(vm, String::from_utf8("true"sv));
             }
         }
 
@@ -528,10 +526,10 @@ ThrowCompletionOr<LocaleResult> resolve_locale(VM& vm, Vector<DeprecatedString>
 }
 
 // 9.2.8 LookupSupportedLocales ( availableLocales, requestedLocales ), https://tc39.es/ecma402/#sec-lookupsupportedlocales
-static ThrowCompletionOr<Vector<DeprecatedString>> lookup_supported_locales(VM& vm, Vector<DeprecatedString> const& requested_locales)
+static ThrowCompletionOr<Vector<String>> lookup_supported_locales(VM& vm, Vector<String> const& requested_locales)
 {
     // 1. Let subset be a new empty List.
-    Vector<DeprecatedString> subset;
+    Vector<String> subset;
 
     // 2. For each element locale of requestedLocales, do
     for (auto const& locale : requested_locales) {
@@ -540,7 +538,7 @@ static ThrowCompletionOr<Vector<DeprecatedString>> lookup_supported_locales(VM&
 
         // a. Let noExtensionsLocale be the String value that is locale with any Unicode locale extension sequences removed.
         locale_id->remove_extension_type<::Locale::LocaleExtension>();
-        auto no_extensions_locale = locale_id->to_deprecated_string();
+        auto no_extensions_locale = TRY_OR_THROW_OOM(vm, locale_id->to_string());
 
         // b. Let availableLocale be ! BestAvailableLocale(availableLocales, noExtensionsLocale).
         auto available_locale = best_available_locale(no_extensions_locale);
@@ -555,7 +553,7 @@ static ThrowCompletionOr<Vector<DeprecatedString>> lookup_supported_locales(VM&
 }
 
 // 9.2.9 BestFitSupportedLocales ( availableLocales, requestedLocales ), https://tc39.es/ecma402/#sec-bestfitsupportedlocales
-static ThrowCompletionOr<Vector<DeprecatedString>> best_fit_supported_locales(VM& vm, Vector<DeprecatedString> const& requested_locales)
+static ThrowCompletionOr<Vector<String>> best_fit_supported_locales(VM& vm, Vector<String> const& requested_locales)
 {
     // The BestFitSupportedLocales abstract operation returns the subset of the provided BCP 47
     // language priority list requestedLocales for which availableLocales has a matching locale
@@ -567,7 +565,7 @@ static ThrowCompletionOr<Vector<DeprecatedString>> best_fit_supported_locales(VM
 }
 
 // 9.2.10 SupportedLocales ( availableLocales, requestedLocales, options ), https://tc39.es/ecma402/#sec-supportedlocales
-ThrowCompletionOr<Array*> supported_locales(VM& vm, Vector<DeprecatedString> const& requested_locales, Value options)
+ThrowCompletionOr<Array*> supported_locales(VM& vm, Vector<String> const& requested_locales, Value options)
 {
     auto& realm = *vm.current_realm();
 
@@ -577,7 +575,7 @@ ThrowCompletionOr<Array*> supported_locales(VM& vm, Vector<DeprecatedString> con
     // 2. Let matcher be ? GetOption(options, "localeMatcher", string, « "lookup", "best fit" », "best fit").
     auto matcher = TRY(get_option(vm, *options_object, vm.names.localeMatcher, OptionType::String, { "lookup"sv, "best fit"sv }, "best fit"sv));
 
-    Vector<DeprecatedString> supported_locales;
+    Vector<String> supported_locales;
 
     // 3. If matcher is "best fit", then
     if (TRY(matcher.as_string().utf8_string_view()) == "best fit"sv) {
@@ -591,7 +589,7 @@ ThrowCompletionOr<Array*> supported_locales(VM& vm, Vector<DeprecatedString> con
     }
 
     // 5. Return CreateArrayFromList(supportedLocales).
-    return Array::create_from<DeprecatedString>(realm, supported_locales, [&vm](auto& locale) { return PrimitiveString::create(vm, locale); }).ptr();
+    return Array::create_from<String>(realm, supported_locales, [&vm](auto& locale) { return PrimitiveString::create(vm, move(locale)); }).ptr();
 }
 
 // 9.2.12 CoerceOptionsToObject ( options ), https://tc39.es/ecma402/#sec-coerceoptionstoobject
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/AbstractOperations.h b/Userland/Libraries/LibJS/Runtime/Intl/AbstractOperations.h
index c892857f04..3257eaa54f 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/AbstractOperations.h
+++ b/Userland/Libraries/LibJS/Runtime/Intl/AbstractOperations.h
@@ -8,6 +8,7 @@
 
 #include <AK/DeprecatedString.h>
 #include <AK/Span.h>
+#include <AK/String.h>
 #include <AK/Variant.h>
 #include <AK/Vector.h>
 #include <LibJS/Forward.h>
@@ -21,23 +22,23 @@ namespace JS::Intl {
 
 struct LocaleOptions {
     Value locale_matcher;
-    Optional<DeprecatedString> ca; // [[Calendar]]
-    Optional<DeprecatedString> co; // [[Collation]]
-    Optional<DeprecatedString> hc; // [[HourCycle]]
-    Optional<DeprecatedString> kf; // [[CaseFirst]]
-    Optional<DeprecatedString> kn; // [[Numeric]]
-    Optional<DeprecatedString> nu; // [[NumberingSystem]]
+    Optional<String> ca; // [[Calendar]]
+    Optional<String> co; // [[Collation]]
+    Optional<String> hc; // [[HourCycle]]
+    Optional<String> kf; // [[CaseFirst]]
+    Optional<String> kn; // [[Numeric]]
+    Optional<String> nu; // [[NumberingSystem]]
 };
 
 struct LocaleResult {
-    DeprecatedString locale;
-    DeprecatedString data_locale;
-    Optional<DeprecatedString> ca; // [[Calendar]]
-    Optional<DeprecatedString> co; // [[Collation]]
-    Optional<DeprecatedString> hc; // [[HourCycle]]
-    Optional<DeprecatedString> kf; // [[CaseFirst]]
-    Optional<DeprecatedString> kn; // [[Numeric]]
-    Optional<DeprecatedString> nu; // [[NumberingSystem]]
+    String locale;
+    String data_locale;
+    Optional<String> ca; // [[Calendar]]
+    Optional<String> co; // [[Collation]]
+    Optional<String> hc; // [[HourCycle]]
+    Optional<String> kf; // [[CaseFirst]]
+    Optional<String> kn; // [[Numeric]]
+    Optional<String> nu; // [[NumberingSystem]]
 };
 
 struct PatternPartition {
@@ -80,14 +81,14 @@ struct PatternPartitionWithSource : public PatternPartition {
 using StringOrBoolean = Variant<StringView, bool>;
 
 ThrowCompletionOr<Optional<::Locale::LocaleID>> is_structurally_valid_language_tag(VM&, StringView locale);
-ThrowCompletionOr<DeprecatedString> canonicalize_unicode_locale_id(VM&, ::Locale::LocaleID& locale);
+ThrowCompletionOr<String> canonicalize_unicode_locale_id(VM&, ::Locale::LocaleID& locale);
 bool is_well_formed_currency_code(StringView currency);
 bool is_well_formed_unit_identifier(StringView unit_identifier);
-ThrowCompletionOr<Vector<DeprecatedString>> canonicalize_locale_list(VM&, Value locales);
-Optional<DeprecatedString> best_available_locale(StringView locale);
-ThrowCompletionOr<DeprecatedString> insert_unicode_extension_and_canonicalize(VM&, ::Locale::LocaleID locale_id, ::Locale::LocaleExtension extension);
-ThrowCompletionOr<LocaleResult> resolve_locale(VM&, Vector<DeprecatedString> const& requested_locales, LocaleOptions const& options, Span<StringView const> relevant_extension_keys);
-ThrowCompletionOr<Array*> supported_locales(VM&, Vector<DeprecatedString> const& requested_locales, Value options);
+ThrowCompletionOr<Vector<String>> canonicalize_locale_list(VM&, Value locales);
+Optional<StringView> best_available_locale(StringView locale);
+ThrowCompletionOr<String> insert_unicode_extension_and_canonicalize(VM&, ::Locale::LocaleID locale_id, ::Locale::LocaleExtension extension);
+ThrowCompletionOr<LocaleResult> resolve_locale(VM&, Vector<String> const& requested_locales, LocaleOptions const& options, Span<StringView const> relevant_extension_keys);
+ThrowCompletionOr<Array*> supported_locales(VM&, Vector<String> const& requested_locales, Value options);
 ThrowCompletionOr<Object*> coerce_options_to_object(VM&, Value options);
 ThrowCompletionOr<StringOrBoolean> get_string_or_boolean_option(VM&, Object const& options, PropertyKey const& property, Span<StringView const> values, StringOrBoolean true_value, StringOrBoolean falsy_value, StringOrBoolean fallback);
 ThrowCompletionOr<Optional<int>> default_number_option(VM&, Value value, int minimum, int maximum, Optional<int> fallback);
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/Collator.h b/Userland/Libraries/LibJS/Runtime/Intl/Collator.h
index 72d0c84bda..bd319bc801 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/Collator.h
+++ b/Userland/Libraries/LibJS/Runtime/Intl/Collator.h
@@ -7,7 +7,7 @@
 #pragma once
 
 #include <AK/Array.h>
-#include <AK/DeprecatedString.h>
+#include <AK/String.h>
 #include <AK/StringView.h>
 #include <LibJS/Runtime/Intl/CollatorCompareFunction.h>
 #include <LibJS/Runtime/Object.h>
@@ -45,8 +45,8 @@ public:
 
     virtual ~Collator() override = default;
 
-    DeprecatedString const& locale() const { return m_locale; }
-    void set_locale(DeprecatedString locale) { m_locale = move(locale); }
+    String const& locale() const { return m_locale; }
+    void set_locale(String locale) { m_locale = move(locale); }
 
     Usage usage() const { return m_usage; }
     void set_usage(StringView usage);
@@ -60,8 +60,8 @@ public:
     void set_case_first(StringView case_first);
     StringView case_first_string() const;
 
-    DeprecatedString const& collation() const { return m_collation; }
-    void set_collation(DeprecatedString collation) { m_collation = move(collation); }
+    String const& collation() const { return m_collation; }
+    void set_collation(String 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; }
@@ -77,11 +77,11 @@ private:
 
     virtual void visit_edges(Visitor&) override;
 
-    DeprecatedString m_locale;                            // [[Locale]]
+    String m_locale;                                      // [[Locale]]
     Usage m_usage { Usage::Sort };                        // [[Usage]]
     Sensitivity m_sensitivity { Sensitivity::Variant };   // [[Sensitivity]]
     CaseFirst m_case_first { CaseFirst::False };          // [[CaseFirst]]
-    DeprecatedString m_collation;                         // [[Collation]]
+    String m_collation;                                   // [[Collation]]
     bool m_ignore_punctuation { false };                  // [[IgnorePunctuation]]
     bool m_numeric { false };                             // [[Numeric]]
     CollatorCompareFunction* m_bound_compare { nullptr }; // [[BoundCompare]]
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/CollatorConstructor.cpp b/Userland/Libraries/LibJS/Runtime/Intl/CollatorConstructor.cpp
index 705576ea4c..1718d76356 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/CollatorConstructor.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Intl/CollatorConstructor.cpp
@@ -53,7 +53,7 @@ static ThrowCompletionOr<Collator*> initialize_collator(VM& vm, Collator& collat
             return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, collation, "collation"sv);
 
         // 12. Set opt.[[co]] to collation.
-        opt.co = TRY(collation.as_string().deprecated_string());
+        opt.co = TRY(collation.as_string().utf8_string());
     }
 
     // 13. Let numeric be ? GetOption(options, "numeric", boolean, empty, undefined).
@@ -62,14 +62,16 @@ static ThrowCompletionOr<Collator*> initialize_collator(VM& vm, Collator& collat
     // 14. If numeric is not undefined, then
     //     a. Let numeric be ! ToString(numeric).
     // 15. Set opt.[[kn]] to numeric.
-    if (!numeric.is_undefined())
-        opt.kn = MUST(numeric.to_deprecated_string(vm));
+    if (!numeric.is_undefined()) {
+        // NOTE: We TRY this operation only to propagate OOM errors.
+        opt.kn = TRY(numeric.to_string(vm));
+    }
 
     // 16. Let caseFirst be ? GetOption(options, "caseFirst", string, « "upper", "lower", "false" », undefined).
     // 17. Set opt.[[kf]] to caseFirst.
     auto case_first = TRY(get_option(vm, *options, vm.names.caseFirst, OptionType::String, { "upper"sv, "lower"sv, "false"sv }, Empty {}));
     if (!case_first.is_undefined())
-        opt.kf = TRY(case_first.as_string().deprecated_string());
+        opt.kf = TRY(case_first.as_string().utf8_string());
 
     // 18. Let relevantExtensionKeys be %Collator%.[[RelevantExtensionKeys]].
     auto relevant_extension_keys = Collator::relevant_extension_keys();
@@ -83,7 +85,7 @@ static ThrowCompletionOr<Collator*> initialize_collator(VM& vm, Collator& collat
     // 21. Let collation be r.[[co]].
     // 22. If collation is null, let collation be "default".
     // 23. Set collator.[[Collation]] to collation.
-    collator.set_collation(result.co.has_value() ? result.co.release_value() : "default");
+    collator.set_collation(result.co.has_value() ? result.co.release_value() : TRY_OR_THROW_OOM(vm, String::from_utf8("default"sv)));
 
     // 24. If relevantExtensionKeys contains "kn", then
     if (relevant_extension_keys.span().contains_slow("kn"sv) && result.kn.has_value()) {
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/DateTimeFormat.h b/Userland/Libraries/LibJS/Runtime/Intl/DateTimeFormat.h
index 7e9ac01710..4077f664c9 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/DateTimeFormat.h
+++ b/Userland/Libraries/LibJS/Runtime/Intl/DateTimeFormat.h
@@ -8,6 +8,7 @@
 
 #include <AK/Array.h>
 #include <AK/DeprecatedString.h>
+#include <AK/String.h>
 #include <AK/StringView.h>
 #include <AK/Time.h>
 #include <AK/Types.h>
@@ -43,17 +44,17 @@ public:
 
     virtual ~DateTimeFormat() override = default;
 
-    DeprecatedString const& locale() const { return m_locale; }
-    void set_locale(DeprecatedString locale) { m_locale = move(locale); }
+    String const& locale() const { return m_locale; }
+    void set_locale(String locale) { m_locale = move(locale); }
 
-    DeprecatedString const& data_locale() const { return m_data_locale; }
-    void set_data_locale(DeprecatedString data_locale) { m_data_locale = move(data_locale); }
+    String const& data_locale() const { return m_data_locale; }
+    void set_data_locale(String data_locale) { m_data_locale = move(data_locale); }
 
-    DeprecatedString const& calendar() const { return m_calendar; }
-    void set_calendar(DeprecatedString calendar) { m_calendar = move(calendar); }
+    String const& calendar() const { return m_calendar; }
+    void set_calendar(String calendar) { m_calendar = move(calendar); }
 
-    DeprecatedString const& numbering_system() const { return m_numbering_system; }
-    void set_numbering_system(DeprecatedString numbering_system) { m_numbering_system = move(numbering_system); }
+    String const& numbering_system() const { return m_numbering_system; }
+    void set_numbering_system(String numbering_system) { m_numbering_system = move(numbering_system); }
 
     bool has_hour_cycle() const { return m_hour_cycle.has_value(); }
     ::Locale::HourCycle hour_cycle() const { return *m_hour_cycle; }
@@ -134,9 +135,9 @@ private:
 
     virtual void visit_edges(Visitor&) override;
 
-    DeprecatedString m_locale;                               // [[Locale]]
-    DeprecatedString m_calendar;                             // [[Calendar]]
-    DeprecatedString m_numbering_system;                     // [[NumberingSystem]]
+    String m_locale;                                         // [[Locale]]
+    String m_calendar;                                       // [[Calendar]]
+    String m_numbering_system;                               // [[NumberingSystem]]
     Optional<::Locale::HourCycle> m_hour_cycle;              // [[HourCycle]]
     DeprecatedString m_time_zone;                            // [[TimeZone]]
     Optional<Style> m_date_style;                            // [[DateStyle]]
@@ -144,7 +145,7 @@ private:
     Vector<::Locale::CalendarRangePattern> m_range_patterns; // [[RangePatterns]]
     NativeFunction* m_bound_format { nullptr };              // [[BoundFormat]]
 
-    DeprecatedString m_data_locale;
+    String m_data_locale;
 };
 
 enum class OptionRequired {
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/DateTimeFormatConstructor.cpp b/Userland/Libraries/LibJS/Runtime/Intl/DateTimeFormatConstructor.cpp
index 389469c97b..52781e3aff 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/DateTimeFormatConstructor.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Intl/DateTimeFormatConstructor.cpp
@@ -110,7 +110,7 @@ ThrowCompletionOr<DateTimeFormat*> initialize_date_time_format(VM& vm, DateTimeF
             return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, calendar, "calendar"sv);
 
         // 8. Set opt.[[ca]] to calendar.
-        opt.ca = TRY(calendar.as_string().deprecated_string());
+        opt.ca = TRY(calendar.as_string().utf8_string());
     }
 
     // 9. Let numberingSystem be ? GetOption(options, "numberingSystem", string, empty, undefined).
@@ -123,7 +123,7 @@ ThrowCompletionOr<DateTimeFormat*> initialize_date_time_format(VM& vm, DateTimeF
             return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, numbering_system, "numberingSystem"sv);
 
         // 11. Set opt.[[nu]] to numberingSystem.
-        opt.nu = TRY(numbering_system.as_string().deprecated_string());
+        opt.nu = TRY(numbering_system.as_string().utf8_string());
     }
 
     // 12. Let hour12 be ? GetOption(options, "hour12", boolean, empty, undefined).
@@ -140,7 +140,7 @@ ThrowCompletionOr<DateTimeFormat*> initialize_date_time_format(VM& vm, DateTimeF
 
     // 15. Set opt.[[hc]] to hourCycle.
     if (!hour_cycle.is_nullish())
-        opt.hc = TRY(hour_cycle.as_string().deprecated_string());
+        opt.hc = TRY(hour_cycle.as_string().utf8_string());
 
     // 16. Let localeData be %DateTimeFormat%.[[LocaleData]].
     // 17. Let r be ResolveLocale(%DateTimeFormat%.[[AvailableLocales]], requestedLocales, opt, %DateTimeFormat%.[[RelevantExtensionKeys]], localeData).
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/DisplayNames.h b/Userland/Libraries/LibJS/Runtime/Intl/DisplayNames.h
index 008ee5f574..ebe0a55f9c 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/DisplayNames.h
+++ b/Userland/Libraries/LibJS/Runtime/Intl/DisplayNames.h
@@ -6,8 +6,8 @@
 
 #pragma once
 
-#include <AK/DeprecatedString.h>
 #include <AK/Optional.h>
+#include <AK/String.h>
 #include <AK/StringView.h>
 #include <LibJS/Runtime/Object.h>
 #include <LibLocale/Locale.h>
@@ -41,8 +41,8 @@ class DisplayNames final : public Object {
 public:
     virtual ~DisplayNames() override = default;
 
-    DeprecatedString const& locale() const { return m_locale; }
-    void set_locale(DeprecatedString locale) { m_locale = move(locale); }
+    String const& locale() const { return m_locale; }
+    void set_locale(String locale) { m_locale = move(locale); }
 
     ::Locale::Style style() const { return m_style; }
     void set_style(StringView style) { m_style = ::Locale::style_from_string(style); }
@@ -64,7 +64,7 @@ public:
 private:
     DisplayNames(Object& prototype);
 
-    DeprecatedString m_locale;                         // [[Locale]]
+    String m_locale;                                   // [[Locale]]
     ::Locale::Style m_style { ::Locale::Style::Long }; // [[Style]]
     Type m_type { Type::Invalid };                     // [[Type]]
     Fallback m_fallback { Fallback::Invalid };         // [[Fallback]]
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/DurationFormat.h b/Userland/Libraries/LibJS/Runtime/Intl/DurationFormat.h
index 17b0b260cc..c298a73392 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/DurationFormat.h
+++ b/Userland/Libraries/LibJS/Runtime/Intl/DurationFormat.h
@@ -9,6 +9,7 @@
 
 #include <AK/Array.h>
 #include <AK/DeprecatedString.h>
+#include <AK/String.h>
 #include <LibJS/Runtime/Intl/AbstractOperations.h>
 #include <LibJS/Runtime/Object.h>
 #include <LibJS/Runtime/Temporal/Duration.h>
@@ -51,18 +52,18 @@ public:
 
     virtual ~DurationFormat() override = default;
 
-    void set_locale(DeprecatedString locale) { m_locale = move(locale); }
-    DeprecatedString const& locale() const { return m_locale; }
+    void set_locale(String locale) { m_locale = move(locale); }
+    String const& locale() const { return m_locale; }
 
-    void set_data_locale(DeprecatedString data_locale) { m_data_locale = move(data_locale); }
-    DeprecatedString const& data_locale() const { return m_data_locale; }
+    void set_data_locale(String data_locale) { m_data_locale = move(data_locale); }
+    String const& data_locale() const { return m_data_locale; }
 
-    void set_numbering_system(DeprecatedString numbering_system) { m_numbering_system = move(numbering_system); }
-    DeprecatedString const& numbering_system() const { return m_numbering_system; }
+    void set_numbering_system(String numbering_system) { m_numbering_system = move(numbering_system); }
+    String const& numbering_system() const { return m_numbering_system; }
 
     void set_style(StringView style) { m_style = style_from_string(style); }
     Style style() const { return m_style; }
-    DeprecatedString style_string() const { return style_to_string(m_style); }
+    StringView style_string() const { return style_to_string(m_style); }
 
     void set_years_style(StringView years_style) { m_years_style = date_style_from_string(years_style); }
     ValueStyle years_style() const { return m_years_style; }
@@ -160,9 +161,9 @@ private:
     static Display display_from_string(StringView display);
     static StringView display_to_string(Display);
 
-    DeprecatedString m_locale;                            // [[Locale]]
-    DeprecatedString m_data_locale;                       // [[DataLocale]]
-    DeprecatedString m_numbering_system;                  // [[NumberingSystem]]
+    String m_locale;                                      // [[Locale]]
+    String m_data_locale;                                 // [[DataLocale]]
+    String m_numbering_system;                            // [[NumberingSystem]]
     Style m_style { Style::Long };                        // [[Style]]
     ValueStyle m_years_style { ValueStyle::Long };        // [[YearsStyle]]
     Display m_years_display { Display::Auto };            // [[YearsDisplay]]
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/DurationFormatConstructor.cpp b/Userland/Libraries/LibJS/Runtime/Intl/DurationFormatConstructor.cpp
index 9896980fa5..204b312beb 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/DurationFormatConstructor.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Intl/DurationFormatConstructor.cpp
@@ -74,7 +74,7 @@ ThrowCompletionOr<NonnullGCPtr<Object>> DurationFormatConstructor::construct(Fun
     // 8. Let opt be the Record { [[localeMatcher]]: matcher, [[nu]]: numberingSystem }.
     LocaleOptions opt {};
     opt.locale_matcher = matcher;
-    opt.nu = numbering_system.is_undefined() ? Optional<DeprecatedString>() : TRY(numbering_system.as_string().deprecated_string());
+    opt.nu = numbering_system.is_undefined() ? Optional<String>() : TRY(numbering_system.as_string().utf8_string());
 
     // 9. Let r be ResolveLocale(%DurationFormat%.[[AvailableLocales]], requestedLocales, opt, %DurationFormat%.[[RelevantExtensionKeys]], %DurationFormat%.[[LocaleData]]).
     auto result = TRY(resolve_locale(vm, requested_locales, opt, DurationFormat::relevant_extension_keys()));
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/ListFormat.h b/Userland/Libraries/LibJS/Runtime/Intl/ListFormat.h
index 8db448bf1b..b5a7fe8645 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/ListFormat.h
+++ b/Userland/Libraries/LibJS/Runtime/Intl/ListFormat.h
@@ -8,6 +8,7 @@
 
 #include <AK/DeprecatedString.h>
 #include <AK/HashMap.h>
+#include <AK/String.h>
 #include <AK/StringView.h>
 #include <AK/Variant.h>
 #include <AK/Vector.h>
@@ -30,8 +31,8 @@ public:
 
     virtual ~ListFormat() override = default;
 
-    DeprecatedString const& locale() const { return m_locale; }
-    void set_locale(DeprecatedString locale) { m_locale = move(locale); }
+    String const& locale() const { return m_locale; }
+    void set_locale(String locale) { m_locale = move(locale); }
 
     Type type() const { return m_type; }
     void set_type(StringView type);
@@ -44,7 +45,7 @@ public:
 private:
     explicit ListFormat(Object& prototype);
 
-    DeprecatedString m_locale;                         // [[Locale]]
+    String m_locale;                                   // [[Locale]]
     Type m_type { Type::Invalid };                     // [[Type]]
     ::Locale::Style m_style { ::Locale::Style::Long }; // [[Style]]
 };
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/Locale.cpp b/Userland/Libraries/LibJS/Runtime/Intl/Locale.cpp
index 9143ad0ff5..7acac0a58c 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/Locale.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Intl/Locale.cpp
@@ -14,48 +14,44 @@
 
 namespace JS::Intl {
 
-NonnullGCPtr<Locale> Locale::create(Realm& realm, ::Locale::LocaleID const& locale_id)
+ThrowCompletionOr<NonnullGCPtr<Locale>> Locale::create(Realm& realm, ::Locale::LocaleID locale_id)
 {
-    return realm.heap().allocate<Locale>(realm, locale_id, *realm.intrinsics().intl_locale_prototype());
-}
+    auto locale = realm.heap().allocate<Locale>(realm, *realm.intrinsics().intl_locale_prototype());
+    locale->set_locale(TRY_OR_THROW_OOM(realm.vm(), locale_id.to_string()));
 
-// 14 Locale Objects, https://tc39.es/ecma402/#locale-objects
-Locale::Locale(Object& prototype)
-    : Object(ConstructWithPrototypeTag::Tag, prototype)
-{
-}
-
-Locale::Locale(::Locale::LocaleID const& locale_id, Object& prototype)
-    : Object(ConstructWithPrototypeTag::Tag, prototype)
-{
-    set_locale(locale_id.to_deprecated_string());
-
-    for (auto const& extension : locale_id.extensions) {
+    for (auto& extension : locale_id.extensions) {
         if (!extension.has<::Locale::LocaleExtension>())
             continue;
 
-        for (auto const& keyword : extension.get<::Locale::LocaleExtension>().keywords) {
-            if (keyword.key == "ca"sv) {
-                set_calendar(keyword.value.to_deprecated_string());
-            } else if (keyword.key == "co"sv) {
-                set_collation(keyword.value.to_deprecated_string());
-            } else if (keyword.key == "hc"sv) {
-                set_hour_cycle(keyword.value.to_deprecated_string());
-            } else if (keyword.key == "kf"sv) {
-                set_case_first(keyword.value.to_deprecated_string());
-            } else if (keyword.key == "kn"sv) {
-                set_numeric(keyword.value.is_empty());
-            } else if (keyword.key == "nu"sv) {
-                set_numbering_system(keyword.value.to_deprecated_string());
-            }
+        for (auto& keyword : extension.get<::Locale::LocaleExtension>().keywords) {
+            if (keyword.key == "ca"sv)
+                locale->set_calendar(move(keyword.value));
+            else if (keyword.key == "co"sv)
+                locale->set_collation(move(keyword.value));
+            else if (keyword.key == "hc"sv)
+                locale->set_hour_cycle(move(keyword.value));
+            else if (keyword.key == "kf"sv)
+                locale->set_case_first(move(keyword.value));
+            else if (keyword.key == "kn"sv)
+                locale->set_numeric(keyword.value.is_empty());
+            else if (keyword.key == "nu"sv)
+                locale->set_numbering_system(move(keyword.value));
         }
 
         break;
     }
+
+    return locale;
+}
+
+// 14 Locale Objects, https://tc39.es/ecma402/#locale-objects
+Locale::Locale(Object& prototype)
+    : Object(ConstructWithPrototypeTag::Tag, prototype)
+{
 }
 
 // 1.1.1 CreateArrayFromListOrRestricted ( list , restricted )
-static Array* create_array_from_list_or_restricted(VM& vm, Vector<StringView> list, Optional<DeprecatedString> restricted)
+static Array* create_array_from_list_or_restricted(VM& vm, Vector<StringView> list, Optional<String> restricted)
 {
     auto& realm = *vm.current_realm();
 
@@ -75,7 +71,7 @@ static Array* create_array_from_list_or_restricted(VM& vm, Vector<StringView> li
 Array* calendars_of_locale(VM& vm, Locale const& locale_object)
 {
     // 1. Let restricted be loc.[[Calendar]].
-    Optional<DeprecatedString> restricted = locale_object.has_calendar() ? locale_object.calendar() : Optional<DeprecatedString> {};
+    Optional<String> restricted = locale_object.has_calendar() ? locale_object.calendar() : Optional<String> {};
 
     // 2. Let locale be loc.[[Locale]].
     auto const& locale = locale_object.locale();
@@ -94,7 +90,7 @@ Array* calendars_of_locale(VM& vm, Locale const& locale_object)
 Array* collations_of_locale(VM& vm, Locale const& locale_object)
 {
     // 1. Let restricted be loc.[[Collation]].
-    Optional<DeprecatedString> restricted = locale_object.has_collation() ? locale_object.collation() : Optional<DeprecatedString> {};
+    Optional<String> restricted = locale_object.has_collation() ? locale_object.collation() : Optional<String> {};
 
     // 2. Let locale be loc.[[Locale]].
     auto const& locale = locale_object.locale();
@@ -113,7 +109,7 @@ Array* collations_of_locale(VM& vm, Locale const& locale_object)
 Array* hour_cycles_of_locale(VM& vm, Locale const& locale_object)
 {
     // 1. Let restricted be loc.[[HourCycle]].
-    Optional<DeprecatedString> restricted = locale_object.has_hour_cycle() ? locale_object.hour_cycle() : Optional<DeprecatedString> {};
+    Optional<String> restricted = locale_object.has_hour_cycle() ? locale_object.hour_cycle() : Optional<String> {};
 
     // 2. Let locale be loc.[[Locale]].
     auto const& locale = locale_object.locale();
@@ -132,7 +128,7 @@ Array* hour_cycles_of_locale(VM& vm, Locale const& locale_object)
 Array* numbering_systems_of_locale(VM& vm, Locale const& locale_object)
 {
     // 1. Let restricted be loc.[[NumberingSystem]].
-    Optional<DeprecatedString> restricted = locale_object.has_numbering_system() ? locale_object.numbering_system() : Optional<DeprecatedString> {};
+    Optional<String> restricted = locale_object.has_numbering_system() ? locale_object.numbering_system() : Optional<String> {};
 
     // 2. Let locale be loc.[[Locale]].
     auto const& locale = locale_object.locale();
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/Locale.h b/Userland/Libraries/LibJS/Runtime/Intl/Locale.h
index 1a3bfafe94..05a059c39a 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/Locale.h
+++ b/Userland/Libraries/LibJS/Runtime/Intl/Locale.h
@@ -7,8 +7,8 @@
 #pragma once
 
 #include <AK/Array.h>
-#include <AK/DeprecatedString.h>
 #include <AK/Optional.h>
+#include <AK/String.h>
 #include <AK/Vector.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/Object.h>
@@ -21,7 +21,7 @@ class Locale final : public Object {
     JS_OBJECT(Locale, Object);
 
 public:
-    static NonnullGCPtr<Locale> create(Realm&, ::Locale::LocaleID const&);
+    static ThrowCompletionOr<NonnullGCPtr<Locale>> create(Realm&, ::Locale::LocaleID);
 
     static constexpr auto relevant_extension_keys()
     {
@@ -36,43 +36,42 @@ public:
 
     virtual ~Locale() override = default;
 
-    DeprecatedString const& locale() const { return m_locale; }
-    void set_locale(DeprecatedString locale) { m_locale = move(locale); }
+    String const& locale() const { return m_locale; }
+    void set_locale(String locale) { m_locale = move(locale); }
 
     bool has_calendar() const { return m_calendar.has_value(); }
-    DeprecatedString const& calendar() const { return m_calendar.value(); }
-    void set_calendar(DeprecatedString calendar) { m_calendar = move(calendar); }
+    String const& calendar() const { return m_calendar.value(); }
+    void set_calendar(String calendar) { m_calendar = move(calendar); }
 
     bool has_case_first() const { return m_case_first.has_value(); }
-    DeprecatedString const& case_first() const { return m_case_first.value(); }
-    void set_case_first(DeprecatedString case_first) { m_case_first = move(case_first); }
+    String const& case_first() const { return m_case_first.value(); }
+    void set_case_first(String case_first) { m_case_first = move(case_first); }
 
     bool has_collation() const { return m_collation.has_value(); }
-    DeprecatedString const& collation() const { return m_collation.value(); }
-    void set_collation(DeprecatedString collation) { m_collation = move(collation); }
+    String const& collation() const { return m_collation.value(); }
+    void set_collation(String collation) { m_collation = move(collation); }
 
     bool has_hour_cycle() const { return m_hour_cycle.has_value(); }
-    DeprecatedString const& hour_cycle() const { return m_hour_cycle.value(); }
-    void set_hour_cycle(DeprecatedString hour_cycle) { m_hour_cycle = move(hour_cycle); }
+    String const& hour_cycle() const { return m_hour_cycle.value(); }
+    void set_hour_cycle(String hour_cycle) { m_hour_cycle = move(hour_cycle); }
 
     bool has_numbering_system() const { return m_numbering_system.has_value(); }
-    DeprecatedString const& numbering_system() const { return m_numbering_system.value(); }
-    void set_numbering_system(DeprecatedString numbering_system) { m_numbering_system = move(numbering_system); }
+    String const& numbering_system() const { return m_numbering_system.value(); }
+    void set_numbering_system(String numbering_system) { m_numbering_system = move(numbering_system); }
 
     bool numeric() const { return m_numeric; }
     void set_numeric(bool numeric) { m_numeric = numeric; }
 
 private:
     explicit Locale(Object& prototype);
-    Locale(::Locale::LocaleID const&, Object& prototype);
-
-    DeprecatedString m_locale;                     // [[Locale]]
-    Optional<DeprecatedString> m_calendar;         // [[Calendar]]
-    Optional<DeprecatedString> m_case_first;       // [[CaseFirst]]
-    Optional<DeprecatedString> m_collation;        // [[Collation]]
-    Optional<DeprecatedString> m_hour_cycle;       // [[HourCycle]]
-    Optional<DeprecatedString> m_numbering_system; // [[NumberingSystem]]
-    bool m_numeric { false };                      // [[Numeric]]
+
+    String m_locale;                     // [[Locale]]
+    Optional<String> m_calendar;         // [[Calendar]]
+    Optional<String> m_case_first;       // [[CaseFirst]]
+    Optional<String> m_collation;        // [[Collation]]
+    Optional<String> m_hour_cycle;       // [[HourCycle]]
+    Optional<String> m_numbering_system; // [[NumberingSystem]]
+    bool m_numeric { false };            // [[Numeric]]
 };
 
 // Table 1: WeekInfo Record Fields, https://tc39.es/proposal-intl-locale-info/#table-locale-weekinfo-record
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/LocaleConstructor.cpp b/Userland/Libraries/LibJS/Runtime/Intl/LocaleConstructor.cpp
index fe5a7492a4..3bcd7653d2 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/LocaleConstructor.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Intl/LocaleConstructor.cpp
@@ -41,7 +41,7 @@ static ThrowCompletionOr<Optional<String>> get_string_option(VM& vm, Object cons
 }
 
 // 14.1.2 ApplyOptionsToTag ( tag, options ), https://tc39.es/ecma402/#sec-apply-options-to-tag
-static ThrowCompletionOr<DeprecatedString> apply_options_to_tag(VM& vm, StringView tag, Object const& options)
+static ThrowCompletionOr<String> apply_options_to_tag(VM& vm, StringView tag, Object const& options)
 {
     // 1. Assert: Type(tag) is String.
     // 2. Assert: Type(options) is Object.
@@ -200,7 +200,7 @@ static ThrowCompletionOr<LocaleAndKeys> apply_unicode_extension_to_tag(VM& vm, S
 
     // 7. Let locale be the String value that is tag with any Unicode locale extension sequences removed.
     locale_id->remove_extension_type<::Locale::LocaleExtension>();
-    auto locale = locale_id->to_string().release_value_but_fixme_should_propagate_errors();
+    auto locale = TRY_OR_THROW_OOM(vm, locale_id->to_string());
 
     // 8. Let newExtension be a Unicode BCP 47 U Extension based on attributes and keywords.
     ::Locale::LocaleExtension new_extension { move(attributes), move(keywords) };
@@ -208,7 +208,7 @@ static ThrowCompletionOr<LocaleAndKeys> apply_unicode_extension_to_tag(VM& vm, S
     // 9. If newExtension is not the empty String, then
     if (!new_extension.attributes.is_empty() || !new_extension.keywords.is_empty()) {
         // a. Let locale be ! InsertUnicodeExtensionAndCanonicalize(locale, newExtension).
-        locale = TRY_OR_THROW_OOM(vm, String::from_deprecated_string(TRY(insert_unicode_extension_and_canonicalize(vm, locale_id.release_value(), move(new_extension)))));
+        locale = TRY(insert_unicode_extension_and_canonicalize(vm, locale_id.release_value(), move(new_extension)));
     }
 
     // 10. Set result.[[locale]] to locale.
@@ -262,7 +262,7 @@ ThrowCompletionOr<NonnullGCPtr<Object>> LocaleConstructor::construct(FunctionObj
     // 6. Let locale be ? OrdinaryCreateFromConstructor(NewTarget, "%Locale.prototype%", internalSlotsList).
     auto locale = TRY(ordinary_create_from_constructor<Locale>(vm, new_target, &Intrinsics::intl_locale_prototype));
 
-    DeprecatedString tag;
+    String tag;
 
     // 7. If Type(tag) is not String or Object, throw a TypeError exception.
     if (!tag_value.is_string() && !tag_value.is_object())
@@ -277,7 +277,7 @@ ThrowCompletionOr<NonnullGCPtr<Object>> LocaleConstructor::construct(FunctionObj
     // 9. Else,
     else {
         // a. Let tag be ? ToString(tag).
-        tag = TRY(tag_value.to_deprecated_string(vm));
+        tag = TRY(tag_value.to_string(vm));
     }
 
     // 10. Set options to ? CoerceOptionsToObject(options).
@@ -328,28 +328,28 @@ ThrowCompletionOr<NonnullGCPtr<Object>> LocaleConstructor::construct(FunctionObj
     auto result = TRY(apply_unicode_extension_to_tag(vm, tag, move(opt), relevant_extension_keys));
 
     // 30. Set locale.[[Locale]] to r.[[locale]].
-    locale->set_locale(result.locale.to_deprecated_string());
+    locale->set_locale(move(result.locale));
     // 31. Set locale.[[Calendar]] to r.[[ca]].
     if (result.ca.has_value())
-        locale->set_calendar(result.ca->to_deprecated_string());
+        locale->set_calendar(result.ca.release_value());
     // 32. Set locale.[[Collation]] to r.[[co]].
     if (result.co.has_value())
-        locale->set_collation(result.co->to_deprecated_string());
+        locale->set_collation(result.co.release_value());
     // 33. Set locale.[[HourCycle]] to r.[[hc]].
     if (result.hc.has_value())
-        locale->set_hour_cycle(result.hc->to_deprecated_string());
+        locale->set_hour_cycle(result.hc.release_value());
 
     // 34. If relevantExtensionKeys contains "kf", then
     if (relevant_extension_keys.span().contains_slow("kf"sv)) {
         // a. Set locale.[[CaseFirst]] to r.[[kf]].
         if (result.kf.has_value())
-            locale->set_case_first(result.kf->to_deprecated_string());
+            locale->set_case_first(result.kf.release_value());
     }
 
     // 35. If relevantExtensionKeys contains "kn", then
     if (relevant_extension_keys.span().contains_slow("kn"sv)) {
         // a. If SameValue(r.[[kn]], "true") is true or r.[[kn]] is the empty String, then
-        if (result.kn.has_value() && (same_value(PrimitiveString::create(vm, *result.kn), PrimitiveString::create(vm, "true")) || result.kn->is_empty())) {
+        if (result.kn.has_value() && (result.kn == "true"sv || result.kn->is_empty())) {
             // i. Set locale.[[Numeric]] to true.
             locale->set_numeric(true);
         }
@@ -362,7 +362,7 @@ ThrowCompletionOr<NonnullGCPtr<Object>> LocaleConstructor::construct(FunctionObj
 
     // 36. Set locale.[[NumberingSystem]] to r.[[nu]].
     if (result.nu.has_value())
-        locale->set_numbering_system(result.nu->to_deprecated_string());
+        locale->set_numbering_system(result.nu.release_value());
 
     // 37. Return locale.
     return locale;
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/LocalePrototype.cpp b/Userland/Libraries/LibJS/Runtime/Intl/LocalePrototype.cpp
index 382bcb8f5b..5cd19a0f6d 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/LocalePrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Intl/LocalePrototype.cpp
@@ -69,7 +69,8 @@ JS_DEFINE_NATIVE_FUNCTION(LocalePrototype::maximize)
         locale->language_id = maximal.release_value();
 
     // 4. Return ! Construct(%Locale%, maximal).
-    return Locale::create(realm, *locale);
+    // NOTE: We TRY this operation only to propagate OOM errors.
+    return TRY(Locale::create(realm, locale.release_value()));
 }
 
 // 14.3.4 Intl.Locale.prototype.minimize ( ), https://tc39.es/ecma402/#sec-Intl.Locale.prototype.minimize
@@ -89,7 +90,8 @@ JS_DEFINE_NATIVE_FUNCTION(LocalePrototype::minimize)
         locale->language_id = minimal.release_value();
 
     // 4. Return ! Construct(%Locale%, minimal).
-    return Locale::create(realm, *locale);
+    // NOTE: We TRY this operation only to propagate OOM errors.
+    return TRY(Locale::create(realm, locale.release_value()));
 }
 
 // 14.3.5 Intl.Locale.prototype.toString ( ), https://tc39.es/ecma402/#sec-Intl.Locale.prototype.toString
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/NumberFormat.h b/Userland/Libraries/LibJS/Runtime/Intl/NumberFormat.h
index c5d54fad9c..58b2439e36 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/NumberFormat.h
+++ b/Userland/Libraries/LibJS/Runtime/Intl/NumberFormat.h
@@ -9,6 +9,7 @@
 #include <AK/Array.h>
 #include <AK/DeprecatedString.h>
 #include <AK/Optional.h>
+#include <AK/String.h>
 #include <LibJS/Runtime/Intl/AbstractOperations.h>
 #include <LibJS/Runtime/Intl/MathematicalValue.h>
 #include <LibJS/Runtime/Object.h>
@@ -58,11 +59,11 @@ public:
 
     virtual ~NumberFormatBase() override = default;
 
-    DeprecatedString const& locale() const { return m_locale; }
-    void set_locale(DeprecatedString locale) { m_locale = move(locale); }
+    String const& locale() const { return m_locale; }
+    void set_locale(String locale) { m_locale = move(locale); }
 
-    DeprecatedString const& data_locale() const { return m_data_locale; }
-    void set_data_locale(DeprecatedString data_locale) { m_data_locale = move(data_locale); }
+    String const& data_locale() const { return m_data_locale; }
+    void set_data_locale(String data_locale) { m_data_locale = move(data_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; }
@@ -102,8 +103,8 @@ protected:
     explicit NumberFormatBase(Object& prototype);
 
 private:
-    DeprecatedString m_locale;                                                    // [[Locale]]
-    DeprecatedString m_data_locale;                                               // [[DataLocale]]
+    String m_locale;                                                              // [[Locale]]
+    String m_data_locale;                                                         // [[DataLocale]]
     int m_min_integer_digits { 0 };                                               // [[MinimumIntegerDigits]]
     Optional<int> m_min_fraction_digits {};                                       // [[MinimumFractionDigits]]
     Optional<int> m_max_fraction_digits {};                                       // [[MaximumFractionDigits]]
@@ -178,16 +179,16 @@ public:
 
     virtual ~NumberFormat() override = default;
 
-    DeprecatedString const& numbering_system() const { return m_numbering_system; }
-    void set_numbering_system(DeprecatedString numbering_system) { m_numbering_system = move(numbering_system); }
+    String const& numbering_system() const { return m_numbering_system; }
+    void set_numbering_system(String numbering_system) { m_numbering_system = move(numbering_system); }
 
     Style style() const { return m_style; }
     StringView style_string() const;
     void set_style(StringView style);
 
     bool has_currency() const { return m_currency.has_value(); }
-    DeprecatedString const& currency() const { return m_currency.value(); }
-    void set_currency(DeprecatedString currency) { m_currency = move(currency); }
+    String const& currency() const { return m_currency.value(); }
+    void set_currency(String currency) { m_currency = move(currency); }
 
     bool has_currency_display() const { return m_currency_display.has_value(); }
     CurrencyDisplay currency_display() const { return *m_currency_display; }
@@ -201,8 +202,8 @@ public:
     void set_currency_sign(StringView set_currency_sign);
 
     bool has_unit() const { return m_unit.has_value(); }
-    DeprecatedString const& unit() const { return m_unit.value(); }
-    void set_unit(DeprecatedString unit) { m_unit = move(unit); }
+    String const& unit() const { return m_unit.value(); }
+    void set_unit(String unit) { m_unit = move(unit); }
 
     bool has_unit_display() const { return m_unit_display.has_value(); }
     ::Locale::Style unit_display() const { return *m_unit_display; }
@@ -238,14 +239,14 @@ private:
 
     virtual void visit_edges(Visitor&) override;
 
-    DeprecatedString m_locale;                           // [[Locale]]
-    DeprecatedString m_data_locale;                      // [[DataLocale]]
-    DeprecatedString m_numbering_system;                 // [[NumberingSystem]]
+    String m_locale;                                     // [[Locale]]
+    String m_data_locale;                                // [[DataLocale]]
+    String m_numbering_system;                           // [[NumberingSystem]]
     Style m_style { Style::Invalid };                    // [[Style]]
-    Optional<DeprecatedString> m_currency {};            // [[Currency]]
+    Optional<String> m_currency {};                      // [[Currency]]
     Optional<CurrencyDisplay> m_currency_display {};     // [[CurrencyDisplay]]
     Optional<CurrencySign> m_currency_sign {};           // [[CurrencySign]]
-    Optional<DeprecatedString> m_unit {};                // [[Unit]]
+    Optional<String> m_unit {};                          // [[Unit]]
     Optional<::Locale::Style> m_unit_display {};         // [[UnitDisplay]]
     UseGrouping m_use_grouping { false };                // [[UseGrouping]]
     Notation m_notation { Notation::Invalid };           // [[Notation]]
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/NumberFormatConstructor.cpp b/Userland/Libraries/LibJS/Runtime/Intl/NumberFormatConstructor.cpp
index a6b1b68543..68f0bf7a32 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/NumberFormatConstructor.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Intl/NumberFormatConstructor.cpp
@@ -107,7 +107,7 @@ ThrowCompletionOr<NumberFormat*> initialize_number_format(VM& vm, NumberFormat&
             return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, numbering_system, "numberingSystem"sv);
 
         // 8. Set opt.[[nu]] to numberingSystem.
-        opt.nu = TRY(numbering_system.as_string().deprecated_string());
+        opt.nu = TRY(numbering_system.as_string().utf8_string());
     }
 
     // 9. Let localeData be %NumberFormat%.[[LocaleData]].
@@ -454,7 +454,7 @@ ThrowCompletionOr<void> set_number_format_unit_options(VM& vm, NumberFormat& int
     // 14. If style is "currency", then
     if (intl_object.style() == NumberFormat::Style::Currency) {
         // a. Set intlObj.[[Currency]] to the ASCII-uppercase of currency.
-        intl_object.set_currency(TRY(currency.as_string().deprecated_string()).to_uppercase());
+        intl_object.set_currency(TRY_OR_THROW_OOM(vm, TRY(currency.as_string().utf8_string()).to_uppercase()));
 
         // c. Set intlObj.[[CurrencyDisplay]] to currencyDisplay.
         intl_object.set_currency_display(TRY(currency_display.as_string().utf8_string_view()));
@@ -466,7 +466,7 @@ ThrowCompletionOr<void> set_number_format_unit_options(VM& vm, NumberFormat& int
     // 15. If style is "unit", then
     if (intl_object.style() == NumberFormat::Style::Unit) {
         // a. Set intlObj.[[Unit]] to unit.
-        intl_object.set_unit(TRY(unit.as_string().utf8_string_view()));
+        intl_object.set_unit(TRY(unit.as_string().utf8_string()));
 
         // b. Set intlObj.[[UnitDisplay]] to unitDisplay.
         intl_object.set_unit_display(TRY(unit_display.as_string().utf8_string_view()));
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.h b/Userland/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.h
index 1a3e45a0a7..947573565a 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.h
+++ b/Userland/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.h
@@ -8,6 +8,7 @@
 
 #include <AK/Array.h>
 #include <AK/DeprecatedString.h>
+#include <AK/String.h>
 #include <AK/StringView.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/Intl/AbstractOperations.h>
@@ -35,14 +36,14 @@ public:
 
     virtual ~RelativeTimeFormat() override = default;
 
-    DeprecatedString const& locale() const { return m_locale; }
-    void set_locale(DeprecatedString locale) { m_locale = move(locale); }
+    String const& locale() const { return m_locale; }
+    void set_locale(String locale) { m_locale = move(locale); }
 
-    DeprecatedString const& data_locale() const { return m_data_locale; }
-    void set_data_locale(DeprecatedString data_locale) { m_data_locale = move(data_locale); }
+    String const& data_locale() const { return m_data_locale; }
+    void set_data_locale(String data_locale) { m_data_locale = move(data_locale); }
 
-    DeprecatedString const& numbering_system() const { return m_numbering_system; }
-    void set_numbering_system(DeprecatedString numbering_system) { m_numbering_system = move(numbering_system); }
+    String const& numbering_system() const { return m_numbering_system; }
+    void set_numbering_system(String numbering_system) { m_numbering_system = move(numbering_system); }
 
     ::Locale::Style style() const { return m_style; }
     void set_style(StringView style) { m_style = ::Locale::style_from_string(style); }
@@ -63,9 +64,9 @@ private:
 
     virtual void visit_edges(Cell::Visitor&) override;
 
-    DeprecatedString m_locale;                         // [[Locale]]
-    DeprecatedString m_data_locale;                    // [[DataLocale]]
-    DeprecatedString m_numbering_system;               // [[NumberingSystem]]
+    String m_locale;                                   // [[Locale]]
+    String m_data_locale;                              // [[DataLocale]]
+    String m_numbering_system;                         // [[NumberingSystem]]
     ::Locale::Style m_style { ::Locale::Style::Long }; // [[Style]]
     Numeric m_numeric { Numeric::Always };             // [[Numeric]]
     NumberFormat* m_number_format { nullptr };         // [[NumberFormat]]
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/RelativeTimeFormatConstructor.cpp b/Userland/Libraries/LibJS/Runtime/Intl/RelativeTimeFormatConstructor.cpp
index 487717ae9d..2381a3b575 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/RelativeTimeFormatConstructor.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Intl/RelativeTimeFormatConstructor.cpp
@@ -105,7 +105,7 @@ ThrowCompletionOr<RelativeTimeFormat*> initialize_relative_time_format(VM& vm, R
             return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, numbering_system, "numberingSystem"sv);
 
         // 8. Set opt.[[nu]] to numberingSystem.
-        opt.nu = TRY(numbering_system.as_string().deprecated_string());
+        opt.nu = TRY(numbering_system.as_string().utf8_string());
     }
 
     // 9. Let localeData be %RelativeTimeFormat%.[[LocaleData]].
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/Segmenter.h b/Userland/Libraries/LibJS/Runtime/Intl/Segmenter.h
index 4034b1b077..e9fc8f1619 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/Segmenter.h
+++ b/Userland/Libraries/LibJS/Runtime/Intl/Segmenter.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/DeprecatedString.h>
+#include <AK/String.h>
 #include <LibJS/Runtime/Object.h>
 
 namespace JS::Intl {
@@ -23,8 +23,8 @@ public:
 
     virtual ~Segmenter() override = default;
 
-    DeprecatedString const& locale() const { return m_locale; }
-    void set_locale(DeprecatedString locale) { m_locale = move(locale); }
+    String const& locale() const { return m_locale; }
+    void set_locale(String locale) { m_locale = move(locale); }
 
     SegmenterGranularity segmenter_granularity() const { return m_segmenter_granularity; }
     void set_segmenter_granularity(StringView);
@@ -33,7 +33,7 @@ public:
 private:
     explicit Segmenter(Object& prototype);
 
-    DeprecatedString m_locale;                                                       // [[Locale]]
+    String m_locale;                                                                 // [[Locale]]
     SegmenterGranularity m_segmenter_granularity { SegmenterGranularity::Grapheme }; // [[SegmenterGranularity]]
 };
 
diff --git a/Userland/Libraries/LibJS/Runtime/StringPrototype.cpp b/Userland/Libraries/LibJS/Runtime/StringPrototype.cpp
index 6e964016b7..7f1a3d63cb 100644
--- a/Userland/Libraries/LibJS/Runtime/StringPrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/StringPrototype.cpp
@@ -901,7 +901,7 @@ static ThrowCompletionOr<String> transform_case(VM& vm, String const& string, Va
 
     // 4. Let noExtensionsLocale be the String value that is requestedLocale with any Unicode locale extension sequences (6.2.1) removed.
     requested_locale->remove_extension_type<Locale::LocaleExtension>();
-    auto no_extensions_locale = requested_locale->to_deprecated_string();
+    auto no_extensions_locale = TRY_OR_THROW_OOM(vm, requested_locale->to_string());
 
     // 5. Let availableLocales be a List with language tags that includes the languages for which the Unicode Character Database contains language sensitive case mappings. Implementations may add additional language tags if they support case mapping for additional locales.
     // 6. Let locale be ! BestAvailableLocale(availableLocales, noExtensionsLocale).