--- a/js/src/builtin/intl/CommonFunctions.js
+++ b/js/src/builtin/intl/CommonFunctions.js
@@ -564,92 +564,16 @@ function parseLanguageTag(locale) {
     if (hasOwn(ts.localeLowercase, grandfatheredMappings))
         updateGrandfatheredMappings(tagObj);
 
     // Return if the complete input was successfully parsed.
     return tagObj;
 }
 
 /**
- * Returns the input normalized to lower case if it matches the
- * 'unicode_language_subtag' production. Otherwise returns null.
- */
-function parseStandaloneLanguage(language) {
-    // unicode_language_subtag = alpha{2,3} | alpha{5,8} ;
-    var length = language.length;
-    if (length < 2 || length === 4 || length > 8 || !IsASCIIAlphaString(language)) {
-        // Four character language subtags are not allowed in Unicode BCP 47
-        // locale identifiers. Also see the comparison to Unicode CLDR locale
-        // identifiers in <https://unicode.org/reports/tr35/#BCP_47_Conformance>.
-        return null;
-    }
-
-    return callFunction(std_String_toLowerCase, language);
-}
-
-/**
- * Returns the input normalized to title case if it matches the
- * 'unicode_script_subtag' production. Otherwise returns null.
- */
-function parseStandaloneScript(script) {
-    // unicode_script_subtag = alpha{4} ;
-    if (script.length !== 4 || !IsASCIIAlphaString(script)) {
-        return null;
-    }
-
-    // The first character of a script code needs to be capitalized.
-    // "hans" -> "Hans"
-    return callFunction(std_String_toUpperCase, script[0]) +
-           callFunction(std_String_toLowerCase, Substring(script, 1, script.length - 1));
-}
-
-/**
- * Returns the input normalized to upper case if it matches the
- * 'unicode_region_subtag' production. Otherwise returns null.
- */
-function parseStandaloneRegion(region) {
-    // unicode_region_subtag = (alpha{2} | digit{3}) ;
-    var length = region.length;
-    if ((length !== 2 || !IsASCIIAlphaString(region)) &&
-        (length !== 3 || !IsASCIIDigitString(region)))
-    {
-        return null;
-    }
-
-    // Region codes need to be in upper-case. "bu" -> "BU"
-    return callFunction(std_String_toUpperCase, region);
-}
-
-/**
- * Returns the input normalized to lower case if it can be parsed as a
- * '(3*8alphanum) *("-" (3*8alphanum))' subtag sequence. Otherwise returns
- * null.
- */
-function parseStandaloneUnicodeExtensionType(type) {
-    // Reuse the BCP 47 parser for Unicode extension types.
-    var ts = new BCP47TokenStream(type);
-    NEXT_TOKEN_OR_RETURN_NULL(ts);
-
-    // Unicode extension 'type' subtags must match the following ABNF.
-    //
-    // type     = (3*8alphanum) *("-" (3*8alphanum))
-    // alphanum = (ALPHA / DIGIT)       ; letters and numbers
-    // ALPHA    = %x41-5A / %x61-7A     ; A-Z / a-z
-    // DIGIT    = %x30-39               ; 0-9
-    do {
-        if (ts.tokenLength < 3 || ts.tokenLength > 8)
-            return null;
-
-        NEXT_TOKEN_OR_RETURN_NULL(ts);
-    } while (ts.token !== NONE);
-
-    return ts.localeLowercase;
-}
-
-/**
  * Return the locale and fields components of the given valid Transform
  * extension subtag.
  */
 function TransformExtensionComponents(extension) {
     assert(typeof extension === "string", "extension is a String value");
     assert(callFunction(std_String_startsWith, extension, "t-"),
            "extension starts with 't-'");
 
@@ -1232,30 +1156,16 @@ function IsASCIIAlphaString(s) {
         var c = callFunction(std_String_charCodeAt, s, i);
         if (!((0x41 <= c && c <= 0x5A) || (0x61 <= c && c <= 0x7A)))
             return false;
     }
     return true;
 }
 
 /**
- * Returns true if the input contains only ASCII digit characters.
- */
-function IsASCIIDigitString(s) {
-    assert(typeof s === "string", "IsASCIIDigitString");
-
-    for (var i = 0; i < s.length; i++) {
-        var c = callFunction(std_String_charCodeAt, s, i);
-        if (!(0x30 <= c && c <= 0x39))
-            return false;
-    }
-    return true;
-}
-
-/**
  * Validates and canonicalizes the given language tag.
  */
 function ValidateAndCanonicalizeLanguageTag(locale) {
     assert(typeof locale === "string", "ValidateAndCanonicalizeLanguageTag");
 
     // Handle the common case (a standalone language) first.
     // Only the following Unicode BCP 47 locale identifier subset is accepted:
     //   unicode_locale_id = unicode_language_id
@@ -1438,19 +1348,19 @@ function CanonicalizeLocaleList(locales)
     // Step 1.
     if (locales === undefined)
         return [];
 
     // Step 3 (and the remaining steps).
     if (typeof locales === "string")
         return [ValidateAndCanonicalizeLanguageTag(locales)];
 
-    var unboxedLocale = callFunction(unboxLocaleOrNull, locales);
+    var unboxedLocale = LocaleToStringOrNull(locales);
     if (unboxedLocale !== null)
-        return [StringFromLanguageTagObject(unboxedLocale.locale)]
+        return [unboxedLocale];
 
     // Step 2.
     var seen = [];
 
     // Step 4.
     var O = ToObject(locales);
 
     // Step 5.
@@ -1466,19 +1376,19 @@ function CanonicalizeLocaleList(locales)
             // Step 7.c.i.
             var kValue = O[k];
 
             // Step 7.c.ii.
             if (!(typeof kValue === "string" || IsObject(kValue)))
                 ThrowTypeError(JSMSG_INVALID_LOCALES_ELEMENT);
 
             // Steps 7.c.iii-iv.
-            var unboxedLocale = callFunction(unboxLocaleOrNull, kValue);
+            var unboxedLocale = LocaleToStringOrNull(kValue);
             var tag = unboxedLocale !== null
-                      ? StringFromLanguageTagObject(unboxedLocale.locale)
+                      ? unboxedLocale
                       : ValidateAndCanonicalizeLanguageTag(ToString(kValue));
 
             // Step 7.c.v.
             if (callFunction(ArrayIndexOf, seen, tag) === -1)
                 _DefineDataProperty(seen, seen.length, tag);
         }
 
         // Step 7.d.

--- a/js/src/builtin/intl/Locale.cpp
+++ b/js/src/builtin/intl/Locale.cpp
@@ -27,618 +27,36 @@
 #include "vm/JSContext.h"
 #include "vm/StringType.h"
 
 #include "vm/JSObject-inl.h"
 #include "vm/NativeObject-inl.h"
 
 using namespace js;
 
-const JSClass LocaleObject::class_ = {
-    js_Object_str,
-    JSCLASS_HAS_RESERVED_SLOTS(LocaleObject::SLOT_COUNT),
-};
-
-static bool locale_toSource(JSContext* cx, unsigned argc, Value* vp) {
-  CallArgs args = CallArgsFromVp(argc, vp);
-  args.rval().setString(cx->names().Locale);
-  return true;
-}
-
-static const JSFunctionSpec locale_methods[] = {
-    JS_SELF_HOSTED_FN("maximize", "Intl_Locale_maximize", 0, 0),
-    JS_SELF_HOSTED_FN("minimize", "Intl_Locale_minimize", 0, 0),
-    JS_SELF_HOSTED_FN("toString", "Intl_Locale_toString", 0, 0),
-    JS_FN(js_toSource_str, locale_toSource, 0, 0), JS_FS_END};
-
-static const JSPropertySpec locale_properties[] = {
-    JS_SELF_HOSTED_GET("baseName", "$Intl_Locale_baseName_get", 0),
-    JS_SELF_HOSTED_GET("calendar", "$Intl_Locale_calendar_get", 0),
-    JS_SELF_HOSTED_GET("collation", "$Intl_Locale_collation_get", 0),
-    JS_SELF_HOSTED_GET("hourCycle", "$Intl_Locale_hourCycle_get", 0),
-    JS_SELF_HOSTED_GET("caseFirst", "$Intl_Locale_caseFirst_get", 0),
-    JS_SELF_HOSTED_GET("numeric", "$Intl_Locale_numeric_get", 0),
-    JS_SELF_HOSTED_GET("numberingSystem", "$Intl_Locale_numberingSystem_get",
-                       0),
-    JS_SELF_HOSTED_GET("language", "$Intl_Locale_language_get", 0),
-    JS_SELF_HOSTED_GET("script", "$Intl_Locale_script_get", 0),
-    JS_SELF_HOSTED_GET("region", "$Intl_Locale_region_get", 0),
-    JS_STRING_SYM_PS(toStringTag, "Intl.Locale", JSPROP_READONLY),
-    JS_PS_END};
-
-static LocaleObject* CreateLocaleObject(JSContext* cx, HandleObject prototype) {
-  RootedObject proto(cx, prototype);
-  if (!proto) {
-    proto = GlobalObject::getOrCreateLocalePrototype(cx, cx->global());
-    if (!proto) {
-      return nullptr;
-    }
-  }
-
-  LocaleObject* locale = NewObjectWithGivenProto<LocaleObject>(cx, proto);
-  if (!locale) {
-    return nullptr;
-  }
-
-  locale->setReservedSlot(LocaleObject::INTERNALS_SLOT, NullValue());
-
-  return locale;
-}
-
-/**
- * Intl.Locale( tag[, options] )
- */
-static bool Locale(JSContext* cx, unsigned argc, Value* vp) {
-  CallArgs args = CallArgsFromVp(argc, vp);
-
-  // Step 1.
-  if (!ThrowIfNotConstructing(cx, args, "Intl.Locale")) {
-    return false;
-  }
-
-  // Steps 2-6 (Inlined 9.1.14, OrdinaryCreateFromConstructor).
-  RootedObject proto(cx);
-  if (!GetPrototypeFromBuiltinConstructor(cx, args, JSProto_Null, &proto)) {
-    return false;
-  }
-
-  Rooted<LocaleObject*> locale(cx, CreateLocaleObject(cx, proto));
-  if (!locale) {
-    return false;
-  }
-
-  HandleValue tag = args.get(0);
-  HandleValue options = args.get(1);
-
-  // Steps 7-37.
-  if (!intl::InitializeObject(cx, locale, cx->names().InitializeLocale, tag,
-                              options)) {
-    return false;
-  }
-
-  // Step 38.
-  args.rval().setObject(*locale);
-  return true;
-}
-
-JSObject* js::CreateLocalePrototype(JSContext* cx, HandleObject Intl,
-                                    Handle<GlobalObject*> global) {
-  RootedFunction ctor(
-      cx, GlobalObject::createConstructor(cx, &Locale, cx->names().Locale, 1));
-  if (!ctor) {
-    return nullptr;
-  }
-
-  RootedObject proto(
-      cx, GlobalObject::createBlankPrototype<PlainObject>(cx, global));
-  if (!proto) {
-    return nullptr;
-  }
-
-  if (!LinkConstructorAndPrototype(cx, ctor, proto)) {
-    return nullptr;
-  }
-
-  if (!DefinePropertiesAndFunctions(cx, proto, locale_properties,
-                                    locale_methods)) {
-    return nullptr;
-  }
-
-  RootedValue ctorValue(cx, ObjectValue(*ctor));
-  if (!DefineDataProperty(cx, Intl, cx->names().Locale, ctorValue, 0)) {
-    return nullptr;
-  }
-
-  return proto;
-}
-
 /* static */ bool js::GlobalObject::addLocaleConstructor(JSContext* cx,
                                                          HandleObject intl) {
   Handle<GlobalObject*> global = cx->global();
 
   {
-    const Value& proto = global->getReservedSlot(LOCALE_PROTO);
-    if (!proto.isUndefined()) {
-      MOZ_ASSERT(proto.isObject());
-      JS_ReportErrorASCII(cx,
-                          "the Locale constructor can't be added multiple "
-                          "times in the same global");
-      return false;
-    }
-  }
-
-  JSObject* localeProto = CreateLocalePrototype(cx, intl, global);
-  if (!localeProto) {
-    return false;
-  }
-
-  global->setReservedSlot(LOCALE_PROTO, ObjectValue(*localeProto));
-
-  {
     const Value& proto = global->getReservedSlot(NATIVE_LOCALE_PROTO);
     if (!proto.isUndefined()) {
       MOZ_ASSERT(proto.isObject());
       JS_ReportErrorASCII(
           cx,
           "the Locale constructor can't be added multiple times in the"
           "same global");
       return false;
     }
   }
 
-  localeProto = CreateNativeLocalePrototype(cx, intl, global);
+  JSObject* localeProto = CreateNativeLocalePrototype(cx, intl, global);
   if (!localeProto) {
     return false;
   }
 
   global->setReservedSlot(NATIVE_LOCALE_PROTO, ObjectValue(*localeProto));
   return true;
 }
 
 bool js::AddLocaleConstructor(JSContext* cx, JS::Handle<JSObject*> intl) {
   return GlobalObject::addLocaleConstructor(cx, intl);
 }
-
-bool js::intl_CreateUninitializedLocale(JSContext* cx, unsigned argc,
-                                        Value* vp) {
-  CallArgs args = CallArgsFromVp(argc, vp);
-  MOZ_ASSERT(args.length() == 0);
-
-  LocaleObject* locale = CreateLocaleObject(cx, nullptr);
-  if (!locale) {
-    return false;
-  }
-
-  args.rval().setObject(*locale);
-  return true;
-}
-
-#ifdef DEBUG
-
-template <typename CharT>
-struct LanguageTagValidator {
-  bool operator()(mozilla::Range<const CharT> language) const {
-    // Tell the analysis the |std::all_of| function can't GC.
-    JS::AutoSuppressGCAnalysis nogc;
-
-    // BNF: unicode_language_subtag = alpha{2,3} | alpha{5,8} ;
-    // Canonical form is lower case.
-    return ((2 <= language.length() && language.length() <= 3) ||
-            (5 <= language.length() && language.length() <= 8)) &&
-           std::all_of(language.begin().get(), language.end().get(),
-                       mozilla::IsAsciiLowercaseAlpha<CharT>);
-  }
-};
-
-template <typename CharT>
-struct ScriptTagValidator {
-  bool operator()(mozilla::Range<const CharT> script) const {
-    // Tell the analysis the |std::all_of| function can't GC.
-    JS::AutoSuppressGCAnalysis nogc;
-
-    // BNF: unicode_script_subtag = alpha{4} ;
-    // Canonical form is title case.
-    return script.length() == 4 && mozilla::IsAsciiUppercaseAlpha(script[0]) &&
-           std::all_of(std::next(script.begin().get()), script.end().get(),
-                       mozilla::IsAsciiLowercaseAlpha<CharT>);
-  }
-};
-
-template <typename CharT>
-struct RegionTagValidator {
-  bool operator()(mozilla::Range<const CharT> region) const {
-    // Tell the analysis the |std::all_of| function can't GC.
-    JS::AutoSuppressGCAnalysis nogc;
-
-    // BNF: unicode_region_subtag = (alpha{2} | digit{3}) ;
-    // Canonical form is upper case.
-    return (region.length() == 2 &&
-            std::all_of(region.begin().get(), region.end().get(),
-                        mozilla::IsAsciiUppercaseAlpha<CharT>)) ||
-           (region.length() == 3 &&
-            std::all_of(region.begin().get(), region.end().get(),
-                        mozilla::IsAsciiDigit<CharT>));
-  }
-};
-
-template <template <typename> class Validator, typename CharT>
-static bool IsStructurallyValidSubtag(mozilla::Range<const CharT> subtag) {
-  return Validator<CharT>{}(subtag);
-}
-
-template <template <typename> class Validator>
-static bool IsStructurallyValidSubtag(JSLinearString* subtag) {
-  JS::AutoCheckCannotGC nogc;
-  return subtag->hasLatin1Chars()
-             ? Validator<JS::Latin1Char>{}(subtag->latin1Range(nogc))
-             : Validator<char16_t>{}(subtag->twoByteRange(nogc));
-}
-
-template <typename T>
-static bool IsStructurallyValidLanguageTag(const T& language) {
-  return IsStructurallyValidSubtag<LanguageTagValidator>(language);
-}
-
-template <typename T>
-static bool IsStructurallyValidScriptTag(const T& script) {
-  return IsStructurallyValidSubtag<ScriptTagValidator>(script);
-}
-
-template <typename T>
-static bool IsStructurallyValidRegionTag(const T& region) {
-  return IsStructurallyValidSubtag<RegionTagValidator>(region);
-}
-
-#endif /* DEBUG */
-
-// unicode_language_subtag = alpha{2,3} | alpha{5,8} ;
-static constexpr size_t LanguageTagMaxLength = 8;
-
-// unicode_script_subtag = alpha{4} ;
-static constexpr size_t ScriptTagMaxLength = 4;
-
-// unicode_region_subtag = (alpha{2} | digit{3}) ;
-static constexpr size_t RegionTagMaxLength = 3;
-
-// Zero-terminated ICU Locale ID.
-using LocaleId =
-    js::Vector<char, LanguageTagMaxLength + 1 + ScriptTagMaxLength + 1 +
-                         RegionTagMaxLength + 1>;
-
-struct LocaleSubtags {
-  using Subtag = mozilla::Range<const char>;
-
-  Subtag language;
-  Subtag script;
-  Subtag region;
-
-  LocaleSubtags(Subtag language, Subtag script, Subtag region)
-      : language(language), script(script), region(region) {}
-};
-
-// Split the language, script, and region subtags from the input ICU locale ID.
-//
-// ICU provides |uloc_getLanguage|, |uloc_getScript|, and |uloc_getCountry| to
-// retrieve these subtags, but unfortunately these functions are rather slow, so
-// we use our own implementation.
-static LocaleSubtags GetLocaleSubtags(const LocaleId& localeId) {
-  // Locale ID should be zero-terminated for ICU.
-  MOZ_ASSERT(localeId.back() == '\0');
-
-  using Subtag = LocaleSubtags::Subtag;
-
-  // mozilla::Range uses 'const' members, so we can't assign to it. Use |Maybe|
-  // to defer initialization to workaround this.
-  mozilla::Maybe<Subtag> language, script, region;
-
-  size_t subtagStart = 0;
-  for (size_t i = 0; i < localeId.length(); i++) {
-    char c = localeId[i];
-
-    // Skip over any characters until we hit either separator char or the end.
-    if (c != '_' && c != '-' && c != '\0') {
-      continue;
-    }
-
-    size_t length = i - subtagStart;
-    const char* start = localeId.begin() + subtagStart;
-    if (subtagStart == 0) {
-      // unicode_language_subtag = alpha{2,3} | alpha{5,8} ;
-      if ((2 <= length && length <= 3) || (5 <= length && length <= 8)) {
-        language.emplace(start, length);
-        MOZ_ASSERT(IsStructurallyValidLanguageTag(*language));
-      }
-    } else if (length == 4) {
-      // unicode_script_subtag = alpha{4} ;
-      script.emplace(start, length);
-      MOZ_ASSERT(IsStructurallyValidScriptTag(*script));
-    } else if (length == 2 || length == 3) {
-      // unicode_region_subtag = (alpha{2} | digit{3}) ;
-      region.emplace(start, length);
-      MOZ_ASSERT(IsStructurallyValidRegionTag(*region));
-    } else {
-      // Ignore any trailing variant or extension subtags.
-      break;
-    }
-
-    subtagStart = i + 1;
-  }
-
-  return {language.valueOr(Subtag()), script.valueOr(Subtag()),
-          region.valueOr(Subtag())};
-}
-
-enum class LikelySubtags : bool { Add, Remove };
-
-// Return true iff the input subtags are already maximized resp. minimized.
-static bool HasLikelySubtags(LikelySubtags likelySubtags,
-                             JSLinearString* language, JSLinearString* script,
-                             JSLinearString* region) {
-  // The language tag is already maximized if language, script, and region
-  // subtags are present and no placeholder subtags ("und", "Zzzz", "ZZ")
-  // are used.
-  if (likelySubtags == LikelySubtags::Add) {
-    return !StringEqualsLiteral(language, "und") && script &&
-           !StringEqualsLiteral(script, "Zzzz") && region &&
-           !StringEqualsLiteral(region, "ZZ");
-  }
-
-  // The language tag is already minimized if it only contains a language
-  // subtag whose value is not the placeholder value "und".
-  return !StringEqualsLiteral(language, "und") && !script && !region;
-}
-
-// Create an ICU locale ID from the given language, script, and region subtags.
-static bool CreateLocaleForLikelySubtags(JSLinearString* language,
-                                         JSLinearString* script,
-                                         JSLinearString* region,
-                                         LocaleId& locale) {
-  MOZ_ASSERT(locale.length() == 0);
-
-  auto appendSubtag = [&locale](JSLinearString* subtag) {
-    if (locale.length() > 0 && !locale.append('_')) {
-      return false;
-    }
-    if (!locale.growBy(subtag->length())) {
-      return false;
-    }
-    char* dest = locale.end() - subtag->length();
-    CopyChars(reinterpret_cast<Latin1Char*>(dest), *subtag);
-    return true;
-  };
-
-  // Append the language subtag.
-  if (!appendSubtag(language)) {
-    return false;
-  }
-
-  // Append the script subtag if present.
-  if (script && !appendSubtag(script)) {
-    return false;
-  }
-
-  // Append the region subtag if present.
-  if (region && !appendSubtag(region)) {
-    return false;
-  }
-
-  // Zero-terminated for use with ICU.
-  return locale.append('\0');
-}
-
-template <decltype(uloc_addLikelySubtags) likelySubtagsFn>
-static bool CallLikelySubtags(JSContext* cx, const LocaleId& localeId,
-                              LocaleId& result) {
-  // Locale ID must be zero-terminated before passing it to ICU.
-  MOZ_ASSERT(localeId.back() == '\0');
-  MOZ_ASSERT(result.length() == 0);
-
-  // Ensure there's enough room for the result.
-  MOZ_ALWAYS_TRUE(result.resize(LocaleId::InlineLength));
-
-  int32_t length = intl::CallICU(
-      cx,
-      [&localeId](char* chars, int32_t size, UErrorCode* status) {
-        return likelySubtagsFn(localeId.begin(), chars, size, status);
-      },
-      result);
-  if (length < 0) {
-    return false;
-  }
-
-  MOZ_ASSERT(
-      size_t(length) <= LocaleId::InlineLength,
-      "Unexpected extra subtags were added by ICU. If this assertion ever "
-      "fails, simply remove it and move on like nothing ever happended.");
-
-  // Resize the vector to the actual string length.
-  result.shrinkTo(length);
-
-  // Zero-terminated for use with ICU.
-  return result.append('\0');
-}
-
-// Return the array |[language, script or undefined, region or undefined]|.
-static ArrayObject* CreateLikelySubtagsResult(JSContext* cx,
-                                              HandleValue language,
-                                              HandleValue script,
-                                              HandleValue region) {
-  enum LikelySubtagsResult {
-    LikelySubtagsResult_Language = 0,
-    LikelySubtagsResult_Script,
-    LikelySubtagsResult_Region,
-
-    LikelySubtagsResult_Length
-  };
-
-  ArrayObject* result =
-      NewDenseFullyAllocatedArray(cx, LikelySubtagsResult_Length);
-  if (!result) {
-    return nullptr;
-  }
-  result->setDenseInitializedLength(LikelySubtagsResult_Length);
-
-  result->initDenseElement(LikelySubtagsResult_Language, language);
-  result->initDenseElement(LikelySubtagsResult_Script, script);
-  result->initDenseElement(LikelySubtagsResult_Region, region);
-
-  return result;
-}
-
-// The canonical way to compute the Unicode BCP 47 locale identifier with likely
-// subtags is as follows:
-//
-// 1. Call uloc_forLanguageTag() to transform the input locale identifer into an
-//    ICU locale ID.
-// 2. Call uloc_addLikelySubtags() to add the likely subtags to the locale ID.
-// 3. Call uloc_toLanguageTag() to transform the resulting locale ID back into
-//    a Unicode BCP 47 locale identifier.
-//
-// Since uloc_forLanguageTag() and uloc_toLanguageTag() are both kind of slow
-// and we know, by construction, that the input Unicode BCP 47 locale identifier
-// only contains a language, script, and region subtag, we can avoid both calls
-// if we implement their guts ourselves, see CreateLocaleForLikelySubtags().
-// (Where "slow" means about 50% of the execution time of Locale.p.maximize.)
-static ArrayObject* LikelySubtags(JSContext* cx, LikelySubtags likelySubtags,
-                                  const CallArgs& args) {
-  MOZ_ASSERT(args.length() == 3);
-  MOZ_ASSERT(args[0].isString());
-  MOZ_ASSERT(args[1].isString() || args[1].isUndefined());
-  MOZ_ASSERT(args[2].isString() || args[2].isUndefined());
-
-  RootedLinearString language(cx, args[0].toString()->ensureLinear(cx));
-  if (!language) {
-    return nullptr;
-  }
-  MOZ_ASSERT(IsStructurallyValidLanguageTag(language));
-
-  RootedLinearString script(cx);
-  if (args[1].isString()) {
-    script = args[1].toString()->ensureLinear(cx);
-    if (!script) {
-      return nullptr;
-    }
-    MOZ_ASSERT(IsStructurallyValidScriptTag(script));
-  }
-
-  RootedLinearString region(cx);
-  if (args[2].isString()) {
-    region = args[2].toString()->ensureLinear(cx);
-    if (!region) {
-      return nullptr;
-    }
-    MOZ_ASSERT(IsStructurallyValidRegionTag(region));
-  }
-
-  // Return early if the input is already maximized/minimized.
-  if (HasLikelySubtags(likelySubtags, language, script, region)) {
-    return CreateLikelySubtagsResult(cx, args[0], args[1], args[2]);
-  }
-
-  // Create the locale ID for the input arguments.
-  LocaleId locale(cx);
-  if (!CreateLocaleForLikelySubtags(language, script, region, locale)) {
-    return nullptr;
-  }
-
-  // UTS #35 requires that locale ID is maximized before its likely subtags are
-  // removed, so we need to call uloc_addLikelySubtags() for both cases.
-  // See <https://ssl.icu-project.org/trac/ticket/10220> and
-  // <https://ssl.icu-project.org/trac/ticket/12345>.
-
-  LocaleId localeLikelySubtags(cx);
-
-  // Add likely subtags to the locale ID. When minimizing we can skip adding the
-  // likely subtags for already maximized tags. (When maximizing we've already
-  // verified above that the tag is missing likely subtags.)
-  bool addLikelySubtags =
-      likelySubtags == LikelySubtags::Add ||
-      !HasLikelySubtags(LikelySubtags::Add, language, script, region);
-
-  if (addLikelySubtags) {
-    if (!CallLikelySubtags<uloc_addLikelySubtags>(cx, locale,
-                                                  localeLikelySubtags)) {
-      return nullptr;
-    }
-  }
-
-  // Now that we've succesfully maximized the locale, we can minimize it.
-  if (likelySubtags == LikelySubtags::Remove) {
-    if (addLikelySubtags) {
-      // Copy the maximized subtags back into |locale|.
-      locale = std::move(localeLikelySubtags);
-      localeLikelySubtags = LocaleId(cx);
-    }
-
-    // Remove likely subtags from the locale ID.
-    if (!CallLikelySubtags<uloc_minimizeSubtags>(cx, locale,
-                                                 localeLikelySubtags)) {
-      return nullptr;
-    }
-  }
-
-  // Retrieve the individual language, script, and region subtags from the
-  // resulting locale ID.
-  LocaleSubtags subtags = GetLocaleSubtags(localeLikelySubtags);
-
-  // Convert each subtag back to a JSString. Use |undefined| for absent subtags.
-  auto toValue = [cx](const auto& subtag, MutableHandleValue result) {
-    if (subtag.length() > 0) {
-      JSLinearString* str =
-          NewStringCopyN<CanGC>(cx, subtag.begin().get(), subtag.length());
-      if (!str) {
-        return false;
-      }
-      result.setString(str);
-    } else {
-      result.setUndefined();
-    }
-    return true;
-  };
-
-  RootedValue languageValue(cx);
-  if (!toValue(subtags.language, &languageValue)) {
-    return nullptr;
-  }
-  if (languageValue.isUndefined()) {
-    // ICU replaces "und" with the empty string. Handle this case separately.
-    JSLinearString* str = NewStringCopyZ<CanGC>(cx, "und");
-    if (!str) {
-      return nullptr;
-    }
-    languageValue.setString(str);
-  }
-
-  RootedValue scriptValue(cx);
-  if (!toValue(subtags.script, &scriptValue)) {
-    return nullptr;
-  }
-
-  RootedValue regionValue(cx);
-  if (!toValue(subtags.region, &regionValue)) {
-    return nullptr;
-  }
-
-  // Return the language, script, and region subtags in an array.
-  return CreateLikelySubtagsResult(cx, languageValue, scriptValue, regionValue);
-}
-
-bool js::intl_AddLikelySubtags(JSContext* cx, unsigned argc, Value* vp) {
-  CallArgs args = CallArgsFromVp(argc, vp);
-
-  ArrayObject* result = LikelySubtags(cx, LikelySubtags::Add, args);
-  if (!result) {
-    return false;
-  }
-  args.rval().setObject(*result);
-  return true;
-}
-
-bool js::intl_RemoveLikelySubtags(JSContext* cx, unsigned argc, Value* vp) {
-  CallArgs args = CallArgsFromVp(argc, vp);
-
-  ArrayObject* result = LikelySubtags(cx, LikelySubtags::Remove, args);
-  if (!result) {
-    return false;
-  }
-  args.rval().setObject(*result);
-  return true;
-}

--- a/js/src/builtin/intl/Locale.h
+++ b/js/src/builtin/intl/Locale.h
@@ -12,32 +12,16 @@
 #include "builtin/SelfHostingDefines.h"
 #include "js/Class.h"
 #include "vm/NativeObject.h"
 
 namespace js {
 
 class GlobalObject;
 
-class LocaleObject : public NativeObject {
- public:
-  static const JSClass class_;
-
-  static constexpr uint32_t INTERNALS_SLOT = 0;
-  static constexpr uint32_t SLOT_COUNT = 1;
-
-  static_assert(INTERNALS_SLOT == INTL_INTERNALS_OBJECT_SLOT,
-                "INTERNALS_SLOT must match self-hosting define for internals "
-                "object slot");
-};
-
-extern JSObject* CreateLocalePrototype(JSContext* cx,
-                                       JS::Handle<JSObject*> Intl,
-                                       JS::Handle<GlobalObject*> global);
-
 class NativeLocaleObject : public NativeObject {
  public:
   static const JSClass class_;
 
   static constexpr uint32_t LANGUAGE_TAG_SLOT = 0;
   static constexpr uint32_t BASENAME_SLOT = 1;
   static constexpr uint32_t UNICODE_EXTENSION_SLOT = 2;
   static constexpr uint32_t SLOT_COUNT = 3;
@@ -60,36 +44,11 @@ class NativeLocaleObject : public Native
     return getFixedSlot(UNICODE_EXTENSION_SLOT);
   }
 };
 
 extern JSObject* CreateNativeLocalePrototype(JSContext* cx,
                                              JS::Handle<JSObject*> Intl,
                                              JS::Handle<GlobalObject*> global);
 
-/**
- * Creates an uninitialized Intl.Locale object.
- */
-extern MOZ_MUST_USE bool intl_CreateUninitializedLocale(JSContext* cx,
-                                                        unsigned argc,
-                                                        Value* vp);
-
-/**
- * Adds likely subtags to the given canonicalized language BCP47 subtags per
- * the "Add Likely Subtags" algorithm from UTS #35.
- *
- * Usage: subtags = intl_AddLikelySubtags(language, script, region)
- */
-extern MOZ_MUST_USE bool intl_AddLikelySubtags(JSContext* cx, unsigned argc,
-                                               Value* vp);
-
-/**
- * Removes likely subtags from the given canonicalized BCP47 subtags per
- * the "Remove Likely Subtags" algorithm from UTS #35.
- *
- * Usage: subtags = intl_RemoveLikelySubtags(language, script, region)
- */
-extern MOZ_MUST_USE bool intl_RemoveLikelySubtags(JSContext* cx, unsigned argc,
-                                                  Value* vp);
-
 }  // namespace js
 
 #endif /* builtin_intl_Locale_h */

deleted file mode 100644
--- a/js/src/builtin/intl/Locale.js
+++ /dev/null
@@ -1,690 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-/**
- * Intl.Locale internal properties.
- */
-var localeInternalProperties = {
-    relevantExtensionKeys: ["ca", "co", "hc", "kf", "kn", "nu"],
-};
-
-/**
- * ApplyOptionsToTag( tag, options )
- */
-function ApplyOptionsToTag(tagObj, options) {
-    // Steps 1-2 (Already performed in caller).
-
-    // Step 3.
-    var languageOption = GetOption(options, "language", "string", undefined, undefined);
-
-    // Step 4.
-    var language;
-    if (languageOption !== undefined) {
-        language = parseStandaloneLanguage(languageOption);
-        if (language === null)
-            ThrowRangeError(JSMSG_INVALID_OPTION_VALUE, "language", languageOption);
-    }
-
-    // Step 5.
-    var scriptOption = GetOption(options, "script", "string", undefined, undefined);
-
-    // Step 6.
-    var script;
-    if (scriptOption !== undefined) {
-        script = parseStandaloneScript(scriptOption);
-        if (script === null)
-            ThrowRangeError(JSMSG_INVALID_OPTION_VALUE, "script", scriptOption);
-    }
-
-    // Step 7.
-    var regionOption = GetOption(options, "region", "string", undefined, undefined);
-
-    // Step 8.
-    var region;
-    if (regionOption !== undefined) {
-        region = parseStandaloneRegion(regionOption);
-        if (region === null)
-            ThrowRangeError(JSMSG_INVALID_OPTION_VALUE, "region", regionOption);
-    }
-
-    // Step 9 (Already performed in caller).
-
-    // Return early when no subtags were modified.
-    if (language === undefined && script === undefined && region === undefined)
-        return;
-
-    // Step 10.
-    if (language !== undefined)
-        tagObj.language = language;
-
-    // Step 11.
-    if (script !== undefined)
-        tagObj.script = script;
-
-    // Step 12.
-    if (region !== undefined)
-        tagObj.region = region;
-
-    // Replacing the "language" subtag may have turned this locale tag
-    // into a grandfathered language tag. For example consider the
-    // case `new Intl.Locale("en-hakka", {language: "zh"})`, where
-    // "zh-hakka" is a regular grandfathered language tag.
-    if (language !== undefined)
-        updateGrandfatheredMappings(tagObj);
-
-    // Step 13.
-    // Optimized to only update the mappings, because all other canonicalization
-    // steps already happended earlier, so there's no need to repeat them here.
-    updateLocaleIdMappings(tagObj);
-}
-
-/**
- * ApplyUnicodeExtensionToTag( tag, options, relevantExtensionKeys )
- */
-function ApplyUnicodeExtensionToTag(tagObj, options, relevantExtensionKeys) {
-    // Steps 1-2 (Not applicable).
-
-    // Step 3.a
-    // Find the Unicode extension subtag index in |tagObj.extensions|.
-    var extensions = tagObj.extensions;
-    var extensionIndex = -1;
-    for (var i = 0; i < extensions.length; i++) {
-        if (extensions[i][0] === "u") {
-            extensionIndex = i;
-            break;
-        }
-    }
-
-    // If Unicode extensions are neither present in |tagObj| nor in |options|,
-    // we can skip everything below and directly return here.
-    if (extensionIndex < 0) {
-        var hasUnicodeOptions = false;
-        for (var i = 0; i < relevantExtensionKeys.length; i++) {
-            if (options[relevantExtensionKeys[i]] !== undefined) {
-                hasUnicodeOptions = true;
-                break;
-            }
-        }
-        if (!hasUnicodeOptions)
-            return;
-    }
-
-    var attributes, keywords;
-    if (extensionIndex >= 0) {
-        // Step 3.b.
-        var components = UnicodeExtensionComponents(extensions[extensionIndex]);
-
-        // Step 3.c.
-        attributes = components.attributes;
-
-        // Step 3.d.
-        keywords = components.keywords;
-    } else {
-        // Step 4.a.
-        attributes = [];
-
-        // Step 4.b.
-        keywords = [];
-    }
-
-    // Step 5 (Not applicable).
-
-    // Step 6.
-    for (var i = 0; i < relevantExtensionKeys.length; i++) {
-        var key = relevantExtensionKeys[i];
-
-        // Step 6.a.
-        var value = undefined;
-
-        // Steps 6.b-c.
-        var entry = null;
-        for (var j = 0; j < keywords.length; j++) {
-            if (keywords[j].key === key) {
-                entry = keywords[j];
-                value = entry.value;
-                break;
-            }
-        }
-
-        // Step 6.d.
-        assert(hasOwn(key, options), "option value for each extension key present");
-
-        // Step 6.e.
-        var optionsValue = options[key];
-
-        // Step 6.f.
-        if (optionsValue !== undefined) {
-            // Step 6.f.i.
-            assert(typeof optionsValue === "string", "optionsValue is a string");
-
-            // Step 6.f.ii.
-            value = optionsValue;
-
-            // Steps 6.f.iii-iv.
-            if (entry !== null)
-                entry.value = value;
-            else
-                _DefineDataProperty(keywords, keywords.length, {key, value});
-        }
-
-        // Step 6.g (Modify |options| in place).
-        options[key] = value;
-    }
-
-    // Step 7 (Not applicable).
-
-    // Step 8.
-    var newExtension = CanonicalizeUnicodeExtension(attributes, keywords, true);
-
-    // Step 9 (Inlined call to InsertUnicodeExtension).
-    // If the shortcut below step 3.a wasn't taken, the Unicode extension is
-    // definitely non-empty; assert this here.
-    assert(newExtension !== "", "unexpected empty Unicode extension");
-
-    // Update or add the new Unicode extension sequence.
-    if (extensionIndex >= 0) {
-        extensions[extensionIndex] = newExtension;
-    } else {
-        _DefineDataProperty(extensions, extensions.length, newExtension);
-
-        // Extension sequences are sorted by their singleton characters.
-        if (extensions.length > 1) {
-            callFunction(ArraySort, extensions);
-        }
-    }
-
-    // Steps 10-11 (Not applicable).
-}
-
-/**
- * Intl.Locale( tag[, options] )
- */
-function InitializeLocale(locale, tag, options) {
-    // Step 7.
-    if (!(typeof tag === "string" || IsObject(tag)))
-        ThrowTypeError(JSMSG_INVALID_LOCALES_ELEMENT);
-
-    // Steps 8-9.
-    var unboxedLocale = callFunction(unboxLocaleOrNull, tag);
-    if (unboxedLocale === null)
-        tag = ToString(tag);
-
-    // Steps 10-11.
-    var hasOptions = options !== undefined;
-    if (hasOptions)
-        options = ToObject(options);
-
-    // Step 12.
-    var tagObj;
-    if (unboxedLocale === null) {
-        tagObj = parseLanguageTag(tag);
-        if (tagObj === null)
-            ThrowRangeError(JSMSG_INVALID_LANGUAGE_TAG, tag);
-
-        // ApplyOptionsToTag, step 9.
-        CanonicalizeLanguageTagObject(tagObj);
-    } else {
-        tagObj = copyLanguageTagObject(unboxedLocale.locale);
-
-        // |tagObj| is already canonicalized for Intl.Locale objects, so we can
-        // skip ApplyOptionsToTag, step 9.
-    }
-
-    // Step 13.
-    var opt = new Record();
-
-    // Skip rest of step 12 and steps 14-29 if no options were passed to the
-    // Intl.Locale constructor.
-    if (hasOptions) {
-        // Step 12.
-        ApplyOptionsToTag(tagObj, options);
-
-        // Step 14.
-        var calendar = GetOption(options, "calendar", "string", undefined, undefined);
-
-        // Step 15.
-        if (calendar !== undefined) {
-            var standaloneCalendar = parseStandaloneUnicodeExtensionType(calendar);
-            if (standaloneCalendar === null)
-                ThrowRangeError(JSMSG_INVALID_OPTION_VALUE, "calendar", calendar);
-
-            calendar = standaloneCalendar;
-        }
-
-        // Step 16.
-        opt.ca = calendar;
-
-        // Step 17.
-        var collation = GetOption(options, "collation", "string", undefined, undefined);
-
-        // Step 18.
-        if (collation !== undefined) {
-            var standaloneCollation = parseStandaloneUnicodeExtensionType(collation);
-            if (standaloneCollation === null)
-                ThrowRangeError(JSMSG_INVALID_OPTION_VALUE, "collation", collation);
-
-            collation = standaloneCollation;
-        }
-
-        // Step 19.
-        opt.co = collation;
-
-        // Steps 20-21.
-        opt.hc = GetOption(options, "hourCycle", "string", ["h11", "h12", "h23", "h24"],
-                           undefined);
-
-        // Steps 22-23.
-        opt.kf = GetOption(options, "caseFirst", "string", ["upper", "lower", "false"],
-                           undefined);
-
-        // Step 24.
-        var numeric = GetOption(options, "numeric", "boolean", undefined, undefined);
-
-        // Step 25.
-        if (numeric !== undefined)
-            numeric = ToString(numeric);
-
-        // Step 26.
-        opt.kn = numeric;
-
-        // Step 27.
-        var numberingSystem = GetOption(options, "numberingSystem", "string", undefined,
-                                        undefined);
-
-        // Step 28.
-        if (numberingSystem !== undefined) {
-            var standaloneNumberingSystem = parseStandaloneUnicodeExtensionType(numberingSystem);
-            if (standaloneNumberingSystem === null)
-                ThrowRangeError(JSMSG_INVALID_OPTION_VALUE, "numberingSystem", numberingSystem);
-
-            numberingSystem = standaloneNumberingSystem;
-        }
-
-        // Step 29.
-        opt.nu = numberingSystem;
-    } else {
-        // Steps 14-29.
-        opt.ca = undefined;
-        opt.co = undefined;
-        opt.hc = undefined;
-        opt.kf = undefined;
-        opt.kn = undefined;
-        opt.nu = undefined;
-    }
-
-    // Step 2.
-    var {relevantExtensionKeys} = localeInternalProperties;
-
-    // Step 30.
-    if (hasOptions || unboxedLocale === null) {
-        ApplyUnicodeExtensionToTag(tagObj, opt, relevantExtensionKeys);
-    } else {
-        // Directly copy the Unicode extension keys from the source object if
-        // no options were passed to the constructor.
-        opt.ca = unboxedLocale.calendar;
-        opt.co = unboxedLocale.collation;
-        opt.hc = unboxedLocale.hourCycle;
-        opt.kf = unboxedLocale.caseFirst;
-        opt.kn = unboxedLocale.numeric;
-        opt.nu = unboxedLocale.numberingSystem;
-    }
-
-    // Steps 31-37.
-    var internals = new Record();
-    internals.locale = tagObj;
-    internals.calendar = opt.ca;
-    internals.collation = opt.co;
-    internals.hourCycle = opt.hc;
-    internals.caseFirst = opt.kf;
-    internals.numeric = opt.kn === "true" || opt.kn === "";
-    internals.numberingSystem = opt.nu;
-
-    assert(UnsafeGetReservedSlot(locale, INTL_INTERNALS_OBJECT_SLOT) === null,
-           "Internal slot already initialized?");
-    UnsafeSetReservedSlot(locale, INTL_INTERNALS_OBJECT_SLOT, internals);
-}
-
-/**
- * Creates a new Intl.Locale object using the language tag object |tagObj|.
- * The other internal slots are copied over from |otherLocale|.
- */
-function CreateLocale(tagObj, otherLocale) {
-    assert(IsObject(tagObj), "CreateLocale called with non-object");
-    assert(GuardToLocale(otherLocale) !== null, "CreateLocale called with non-Locale");
-
-#ifdef DEBUG
-    var localeTag = StringFromLanguageTagObject(tagObj);
-    assert(localeTag === CanonicalizeLanguageTag(localeTag),
-           "CreateLocale called with non-canonical language tag");
-#endif
-
-    var locInternals = getLocaleInternals(otherLocale);
-
-    var internals = new Record();
-    internals.locale = tagObj;
-    internals.calendar = locInternals.calendar;
-    internals.collation = locInternals.collation;
-    internals.hourCycle = locInternals.hourCycle;
-    internals.caseFirst = locInternals.caseFirst;
-    internals.numeric = locInternals.numeric;
-    internals.numberingSystem = locInternals.numberingSystem;
-
-    var locale = intl_CreateUninitializedLocale();
-    assert(UnsafeGetReservedSlot(locale, INTL_INTERNALS_OBJECT_SLOT) === null,
-                                 "Internal slot already initialized?");
-    UnsafeSetReservedSlot(locale, INTL_INTERNALS_OBJECT_SLOT, internals);
-
-    return locale;
-}
-
-/**
- * Unboxes the |this| argument if it is an Intl.Locale object, otherwise
- * returns null.
- */
-function unboxLocaleOrNull() {
-    if (!IsObject(this))
-        return null;
-
-    var loc = GuardToLocale(this);
-    if (loc !== null)
-        return getLocaleInternals(loc);
-    if (IsWrappedLocale(this))
-        return callFunction(CallLocaleMethodIfWrapped, this, "unboxLocaleOrNull");
-    return null;
-}
-
-/**
- * Creates a copy of the given language tag object.
- */
-function copyLanguageTagObject(tagObj) {
-    assert(IsObject(tagObj), "copyLanguageTagObject called with non-object");
-
-    var variants = [];
-    for (var i = 0; i < tagObj.variants.length; i++)
-        _DefineDataProperty(variants, i, tagObj.variants[i]);
-
-    var extensions = [];
-    for (var i = 0; i < tagObj.extensions.length; i++)
-        _DefineDataProperty(extensions, i, tagObj.extensions[i]);
-
-    return {
-        language: tagObj.language,
-        script: tagObj.script,
-        region: tagObj.region,
-        variants,
-        extensions,
-        privateuse: tagObj.privateuse,
-    };
-}
-
-function getLocaleInternals(obj) {
-    assert(IsObject(obj), "getLocaleInternals called with non-object");
-    assert(GuardToLocale(obj) !== null, "getLocaleInternals called with non-Locale");
-
-    var internals = UnsafeGetReservedSlot(obj, INTL_INTERNALS_OBJECT_SLOT);
-    assert(IsObject(internals), "Internal slot not initialized?");
-
-    return internals;
-}
-
-/**
- * Intl.Locale.prototype.maximize ()
- */
-function Intl_Locale_maximize() {
-    // Step 1.
-    var loc = this;
-
-    // Step 2.
-    if (!IsObject(loc) || (loc = GuardToLocale(loc)) === null)
-        return callFunction(CallLocaleMethodIfWrapped, this, "Intl_Locale_maximize");
-
-    // Step 3.
-    var tagObj = copyLanguageTagObject(getLocaleInternals(loc).locale);
-
-    var maximal = intl_AddLikelySubtags(tagObj.language, tagObj.script, tagObj.region);
-    tagObj.language = maximal[0];
-    tagObj.script = maximal[1];
-    tagObj.region = maximal[2];
-
-    // Update mappings in case ICU returned a non-canonicalized locale.
-    updateLocaleIdMappings(tagObj);
-
-    // Step 4.
-    return CreateLocale(tagObj, loc);
-}
-
-/**
- * Intl.Locale.prototype.minimize ()
- */
-function Intl_Locale_minimize() {
-    // Step 1.
-    var loc = this;
-
-    // Step 2.
-    if (!IsObject(loc) || (loc = GuardToLocale(loc)) === null)
-        return callFunction(CallLocaleMethodIfWrapped, this, "Intl_Locale_minimize");
-
-    // Step 3.
-    var tagObj = copyLanguageTagObject(getLocaleInternals(loc).locale);
-
-    var minimal = intl_RemoveLikelySubtags(tagObj.language, tagObj.script, tagObj.region);
-    tagObj.language = minimal[0];
-    tagObj.script = minimal[1];
-    tagObj.region = minimal[2];
-
-    // Update mappings in case ICU returned a non-canonicalized locale.
-    updateLocaleIdMappings(tagObj);
-
-    // Step 4.
-    return CreateLocale(tagObj, loc);
-}
-
-/**
- * Intl.Locale.prototype.toString ()
- */
-function Intl_Locale_toString() {
-    // Step 1.
-    var loc = this;
-
-    // Step 2.
-    if (!IsObject(loc) || (loc = GuardToLocale(loc)) === null)
-        return callFunction(CallLocaleMethodIfWrapped, this, "Intl_Locale_toString");
-
-    // Step 3.
-    var tagObj = getLocaleInternals(loc).locale;
-    return StringFromLanguageTagObject(tagObj);
-}
-
-/**
- * get Intl.Locale.prototype.baseName
- */
-function $Intl_Locale_baseName_get() {
-    // Step 1.
-    var loc = this;
-
-    // Step 2.
-    if (!IsObject(loc) || (loc = GuardToLocale(loc)) === null)
-        return callFunction(CallLocaleMethodIfWrapped, this, "$Intl_Locale_baseName_get");
-
-    // Step 3.
-    var tagObj = getLocaleInternals(loc).locale;
-
-    // Step 4.
-    // FIXME: spec bug - unicode_locale_id is always matched.
-
-    // Step 5.
-    // FIXME: spec bug - subtag production names not updated.
-    var baseName = tagObj.language;
-
-    if (tagObj.script !== undefined)
-        baseName += "-" + tagObj.script;
-    if (tagObj.region !== undefined)
-        baseName += "-" + tagObj.region;
-    if (tagObj.variants.length > 0)
-        baseName += "-" + callFunction(std_Array_join, tagObj.variants, "-");
-
-    return baseName;
-}
-_SetCanonicalName($Intl_Locale_baseName_get, "get baseName");
-
-/**
- * get Intl.Locale.prototype.calendar
- */
-function $Intl_Locale_calendar_get() {
-    // Step 1.
-    var loc = this;
-
-    // Step 2.
-    if (!IsObject(loc) || (loc = GuardToLocale(loc)) === null)
-        return callFunction(CallLocaleMethodIfWrapped, this, "$Intl_Locale_calendar_get");
-
-    // Step 3.
-    return getLocaleInternals(loc).calendar;
-}
-_SetCanonicalName($Intl_Locale_calendar_get, "get calendar");
-
-/**
- * get Intl.Locale.prototype.collation
- */
-function $Intl_Locale_collation_get() {
-    // Step 1.
-    var loc = this;
-
-    // Step 2.
-    if (!IsObject(loc) || (loc = GuardToLocale(loc)) === null)
-        return callFunction(CallLocaleMethodIfWrapped, this, "$Intl_Locale_collation_get");
-
-    // Step 3.
-    return getLocaleInternals(loc).collation;
-}
-_SetCanonicalName($Intl_Locale_collation_get, "get collation");
-
-/**
- * get Intl.Locale.prototype.hourCycle
- */
-function $Intl_Locale_hourCycle_get() {
-    // Step 1.
-    var loc = this;
-
-    // Step 2.
-    if (!IsObject(loc) || (loc = GuardToLocale(loc)) === null)
-        return callFunction(CallLocaleMethodIfWrapped, this, "$Intl_Locale_hourCycle_get");
-
-    // Step 3.
-    return getLocaleInternals(loc).hourCycle;
-}
-_SetCanonicalName($Intl_Locale_hourCycle_get, "get hourCycle");
-
-/**
- * get Intl.Locale.prototype.caseFirst
- */
-function $Intl_Locale_caseFirst_get() {
-    // Step 1.
-    var loc = this;
-
-    // Step 2.
-    if (!IsObject(loc) || (loc = GuardToLocale(loc)) === null)
-        return callFunction(CallLocaleMethodIfWrapped, this, "$Intl_Locale_caseFirst_get");
-
-    // Step 3.
-    return getLocaleInternals(loc).caseFirst;
-}
-_SetCanonicalName($Intl_Locale_caseFirst_get, "get caseFirst");
-
-/**
- * get Intl.Locale.prototype.numeric
- */
-function $Intl_Locale_numeric_get() {
-    // Step 1.
-    var loc = this;
-
-    // Step 2.
-    if (!IsObject(loc) || (loc = GuardToLocale(loc)) === null)
-        return callFunction(CallLocaleMethodIfWrapped, this, "$Intl_Locale_numeric_get");
-
-    // Step 3.
-    return getLocaleInternals(loc).numeric;
-}
-_SetCanonicalName($Intl_Locale_numeric_get, "get numeric");
-
-/**
- * get Intl.Locale.prototype.numberingSystem
- */
-function $Intl_Locale_numberingSystem_get() {
-    // Step 1.
-    var loc = this;
-
-    // Step 2.
-    if (!IsObject(loc) || (loc = GuardToLocale(loc)) === null)
-        return callFunction(CallLocaleMethodIfWrapped, this, "$Intl_Locale_numberingSystem_get");
-
-    // Step 3.
-    return getLocaleInternals(loc).numberingSystem;
-}
-_SetCanonicalName($Intl_Locale_numberingSystem_get, "get numberingSystem");
-
-/**
- * get Intl.Locale.prototype.language
- */
-function $Intl_Locale_language_get() {
-    // Step 1.
-    var loc = this;
-
-    // Step 2.
-    if (!IsObject(loc) || (loc = GuardToLocale(loc)) === null)
-        return callFunction(CallLocaleMethodIfWrapped, this, "$Intl_Locale_language_get");
-
-    // Step 3.
-    var tagObj = getLocaleInternals(loc).locale;
-
-    // Step 4 (Unnecessary assertion).
-
-    // Step 5.
-    return tagObj.language;
-}
-_SetCanonicalName($Intl_Locale_language_get, "get language");
-
-/**
- * get Intl.Locale.prototype.script
- */
-function $Intl_Locale_script_get() {
-    // Step 1.
-    var loc = this;
-
-    // Step 2.
-    if (!IsObject(loc) || (loc = GuardToLocale(loc)) === null)
-        return callFunction(CallLocaleMethodIfWrapped, this, "$Intl_Locale_script_get");
-
-    // Step 3.
-    var tagObj = getLocaleInternals(loc).locale;
-
-    // Step 4 (Unnecessary assertion).
-
-    // Steps 5-6.
-    // FIXME: spec bug - not all production names updated.
-    return tagObj.script;
-}
-_SetCanonicalName($Intl_Locale_script_get, "get script");
-
-/**
- * get Intl.Locale.prototype.region
- */
-function $Intl_Locale_region_get() {
-    // Step 1.
-    var loc = this;
-
-    // Step 2.
-    if (!IsObject(loc) || (loc = GuardToLocale(loc)) === null)
-        return callFunction(CallLocaleMethodIfWrapped, this, "$Intl_Locale_region_get");
-
-    // Step 3.
-    var tagObj = getLocaleInternals(loc).locale;
-
-    // Step 4 (Unnecessary assertion).
-
-    // Steps 5-6.
-    // FIXME: spec bug - not all production names updated.
-    return tagObj.region;
-}
-_SetCanonicalName($Intl_Locale_region_get, "get region");

--- a/js/src/builtin/intl/NativeLocale.cpp
+++ b/js/src/builtin/intl/NativeLocale.cpp
@@ -1248,14 +1248,14 @@ JSObject* js::CreateNativeLocalePrototyp
   }
 
   if (!DefinePropertiesAndFunctions(cx, proto, locale_native_properties,
                                     locale_native_methods)) {
     return nullptr;
   }
 
   RootedValue ctorValue(cx, ObjectValue(*ctor));
-  if (!DefineDataProperty(cx, Intl, cx->names().locale, ctorValue, 0)) {
+  if (!DefineDataProperty(cx, Intl, cx->names().Locale, ctorValue, 0)) {
     return nullptr;
   }
 
   return proto;
 }

--- a/js/src/jit/InlinableNatives.h
+++ b/js/src/jit/InlinableNatives.h
@@ -26,17 +26,16 @@
   _(AtomicsOr)                                     \
   _(AtomicsXor)                                    \
   _(AtomicsIsLockFree)                             \
                                                    \
   _(Boolean)                                       \
                                                    \
   _(IntlGuardToCollator)                           \
   _(IntlGuardToDateTimeFormat)                     \
-  _(IntlGuardToLocale)                             \
   _(IntlGuardToNumberFormat)                       \
   _(IntlGuardToPluralRules)                        \
   _(IntlGuardToRelativeTimeFormat)                 \
                                                    \
   _(MathAbs)                                       \
   _(MathFloor)                                     \
   _(MathCeil)                                      \
   _(MathRound)                                     \

--- a/js/src/jit/MCallOptimize.cpp
+++ b/js/src/jit/MCallOptimize.cpp
@@ -7,17 +7,16 @@
 #include "mozilla/Casting.h"
 
 #include "jsmath.h"
 
 #include "builtin/AtomicsObject.h"
 #ifdef ENABLE_INTL_API
 #  include "builtin/intl/Collator.h"
 #  include "builtin/intl/DateTimeFormat.h"
-#  include "builtin/intl/Locale.h"
 #  include "builtin/intl/NumberFormat.h"
 #  include "builtin/intl/PluralRules.h"
 #  include "builtin/intl/RelativeTimeFormat.h"
 #endif
 #include "builtin/MapObject.h"
 #include "builtin/String.h"
 #include "builtin/TestingFunctions.h"
 #include "builtin/TypedObject.h"
@@ -106,17 +105,16 @@ static bool CanInlineCrossRealm(Inlinabl
       return true;
 
     case InlinableNative::MathRandom:
       // RNG state is per-realm.
       return false;
 
     case InlinableNative::IntlGuardToCollator:
     case InlinableNative::IntlGuardToDateTimeFormat:
-    case InlinableNative::IntlGuardToLocale:
     case InlinableNative::IntlGuardToNumberFormat:
     case InlinableNative::IntlGuardToPluralRules:
     case InlinableNative::IntlGuardToRelativeTimeFormat:
     case InlinableNative::IsRegExpObject:
     case InlinableNative::RegExpMatcher:
     case InlinableNative::RegExpSearcher:
     case InlinableNative::RegExpTester:
     case InlinableNative::RegExpPrototypeOptimizable:
@@ -314,28 +312,25 @@ IonBuilder::InliningResult IonBuilder::i
       return inlineBoolean(callInfo);
 
 #ifdef ENABLE_INTL_API
     // Intl natives.
     case InlinableNative::IntlGuardToCollator:
       return inlineGuardToClass(callInfo, &CollatorObject::class_);
     case InlinableNative::IntlGuardToDateTimeFormat:
       return inlineGuardToClass(callInfo, &DateTimeFormatObject::class_);
-    case InlinableNative::IntlGuardToLocale:
-      return inlineGuardToClass(callInfo, &LocaleObject::class_);
     case InlinableNative::IntlGuardToNumberFormat:
       return inlineGuardToClass(callInfo, &NumberFormatObject::class_);
     case InlinableNative::IntlGuardToPluralRules:
       return inlineGuardToClass(callInfo, &PluralRulesObject::class_);
     case InlinableNative::IntlGuardToRelativeTimeFormat:
       return inlineGuardToClass(callInfo, &RelativeTimeFormatObject::class_);
 #else
     case InlinableNative::IntlGuardToCollator:
     case InlinableNative::IntlGuardToDateTimeFormat:
-    case InlinableNative::IntlGuardToLocale:
     case InlinableNative::IntlGuardToNumberFormat:
     case InlinableNative::IntlGuardToPluralRules:
     case InlinableNative::IntlGuardToRelativeTimeFormat:
       MOZ_CRASH("Intl API disabled");
 #endif
 
     // Math natives.
     case InlinableNative::MathAbs:

--- a/js/src/moz.build
+++ b/js/src/moz.build
@@ -478,17 +478,16 @@ selfhosted_inputs = [
     'builtin/WeakSet.js'
 ] + ([
     'builtin/intl/Collator.js',
     'builtin/intl/CommonFunctions.js',
     'builtin/intl/CurrencyDataGenerated.js',
     'builtin/intl/DateTimeFormat.js',
     'builtin/intl/IntlObject.js',
     'builtin/intl/LangTagMappingsGenerated.js',
-    'builtin/intl/Locale.js',
     'builtin/intl/NumberFormat.js',
     'builtin/intl/PluralRules.js',
     'builtin/intl/RelativeTimeFormat.js',
     'builtin/intl/UnicodeExtensionsGenerated.js',
 ] if CONFIG['ENABLE_INTL_API'] else [])
 
 # Prepare self-hosted JS code for embedding
 GeneratedFile('selfhosted.out.h', 'selfhosted.js',

--- a/js/src/vm/SelfHosting.cpp
+++ b/js/src/vm/SelfHosting.cpp
@@ -2075,16 +2075,45 @@ static bool intrinsic_ToNumeric(JSContex
   MOZ_ASSERT(args.length() == 1);
   if (!ToNumeric(cx, args[0])) {
     return false;
   }
   args.rval().set(args[0]);
   return true;
 }
 
+static bool intrinsic_LocaleToStringOrNull(JSContext* cx, unsigned argc,
+                                           Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  MOZ_ASSERT(args.length() == 1);
+
+  if (!args[0].isObject()) {
+    args.rval().setNull();
+    return true;
+  }
+
+  JSObject* unwrapped = CheckedUnwrapStatic(&args[0].toObject());
+  if (!unwrapped) {
+    ReportAccessDenied(cx);
+    return false;
+  }
+
+  if (!unwrapped->is<NativeLocaleObject>()) {
+    args.rval().setNull();
+    return true;
+  }
+
+  RootedString str(cx, unwrapped->as<NativeLocaleObject>().languageTag());
+  if (!cx->compartment()->wrap(cx, &str)) {
+    return false;
+  }
+  args.rval().setString(str);
+  return true;
+}
+
 // The self-hosting global isn't initialized with the normal set of builtins.
 // Instead, individual C++-implemented functions that're required by
 // self-hosted code are defined as global functions. Accessing these
 // functions via a content compartment's builtins would be unsafe, because
 // content script might have changed the builtins' prototypes' members.
 // Installing the whole set of builtins in the self-hosting compartment, OTOH,
 // would be wasteful: it increases memory usage and initialization time for
 // self-hosting compartment.
@@ -2450,51 +2479,41 @@ static const JSFunctionSpec intrinsic_fu
           intl_PluralRules_availableLocales, 0, 0),
     JS_FN("intl_GetPluralCategories", intl_GetPluralCategories, 1, 0),
     JS_FN("intl_SelectPluralRule", intl_SelectPluralRule, 2, 0),
     JS_FN("intl_RelativeTimeFormat_availableLocales",
           intl_RelativeTimeFormat_availableLocales, 0, 0),
     JS_FN("intl_FormatRelativeTime", intl_FormatRelativeTime, 4, 0),
     JS_FN("intl_toLocaleLowerCase", intl_toLocaleLowerCase, 2, 0),
     JS_FN("intl_toLocaleUpperCase", intl_toLocaleUpperCase, 2, 0),
-    JS_FN("intl_CreateUninitializedLocale", intl_CreateUninitializedLocale, 0,
-          0),
-    JS_FN("intl_AddLikelySubtags", intl_AddLikelySubtags, 3, 0),
-    JS_FN("intl_RemoveLikelySubtags", intl_RemoveLikelySubtags, 3, 0),
 
     JS_INLINABLE_FN("GuardToCollator", intrinsic_GuardToBuiltin<CollatorObject>,
                     1, 0, IntlGuardToCollator),
     JS_INLINABLE_FN("GuardToDateTimeFormat",
                     intrinsic_GuardToBuiltin<DateTimeFormatObject>, 1, 0,
                     IntlGuardToDateTimeFormat),
-    JS_INLINABLE_FN("GuardToLocale", intrinsic_GuardToBuiltin<LocaleObject>, 1,
-                    0, IntlGuardToLocale),
     JS_INLINABLE_FN("GuardToNumberFormat",
                     intrinsic_GuardToBuiltin<NumberFormatObject>, 1, 0,
                     IntlGuardToNumberFormat),
     JS_INLINABLE_FN("GuardToPluralRules",
                     intrinsic_GuardToBuiltin<PluralRulesObject>, 1, 0,
                     IntlGuardToPluralRules),
     JS_INLINABLE_FN("GuardToRelativeTimeFormat",
                     intrinsic_GuardToBuiltin<RelativeTimeFormatObject>, 1, 0,
                     IntlGuardToRelativeTimeFormat),
 
     JS_FN("IsWrappedDateTimeFormat",
           intrinsic_IsWrappedInstanceOfBuiltin<DateTimeFormatObject>, 1, 0),
-    JS_FN("IsWrappedLocale", intrinsic_IsWrappedInstanceOfBuiltin<LocaleObject>,
-          1, 0),
     JS_FN("IsWrappedNumberFormat",
           intrinsic_IsWrappedInstanceOfBuiltin<NumberFormatObject>, 1, 0),
 
     JS_FN("CallCollatorMethodIfWrapped",
           CallNonGenericSelfhostedMethod<Is<CollatorObject>>, 2, 0),
     JS_FN("CallDateTimeFormatMethodIfWrapped",
           CallNonGenericSelfhostedMethod<Is<DateTimeFormatObject>>, 2, 0),
-    JS_FN("CallLocaleMethodIfWrapped",
-          CallNonGenericSelfhostedMethod<Is<LocaleObject>>, 2, 0),
     JS_FN("CallNumberFormatMethodIfWrapped",
           CallNonGenericSelfhostedMethod<Is<NumberFormatObject>>, 2, 0),
     JS_FN("CallPluralRulesMethodIfWrapped",
           CallNonGenericSelfhostedMethod<Is<PluralRulesObject>>, 2, 0),
     JS_FN("CallRelativeTimeFormatMethodIfWrapped",
           CallNonGenericSelfhostedMethod<Is<RelativeTimeFormatObject>>, 2, 0),
 
     JS_FN("GetDateTimeFormatConstructor",
@@ -2504,16 +2523,18 @@ static const JSFunctionSpec intrinsic_fu
     JS_FN("GetNumberFormatConstructor",
           intrinsic_GetBuiltinIntlConstructor<
               GlobalObject::getOrCreateNumberFormatConstructor>,
           0, 0),
     JS_FN("RuntimeDefaultLocale", intrinsic_RuntimeDefaultLocale, 0, 0),
     JS_FN("IsRuntimeDefaultLocale", intrinsic_IsRuntimeDefaultLocale, 1, 0),
 #endif  // ENABLE_INTL_API
 
+    JS_FN("LocaleToStringOrNull", intrinsic_LocaleToStringOrNull, 1, 0),
+
     JS_FN("GetOwnPropertyDescriptorToArray", GetOwnPropertyDescriptorToArray, 2,
           0),
 
     JS_INLINABLE_FN("IsRegExpObject",
                     intrinsic_IsInstanceOfBuiltin<RegExpObject>, 1, 0,
                     IsRegExpObject),
     JS_FN("CallRegExpMethodIfWrapped",
           CallNonGenericSelfhostedMethod<Is<RegExpObject>>, 2, 0),