diff --git a/.github/workflows/intl4x.yml b/.github/workflows/intl4x.yml
index 13430fbd..d54e48c3 100644
--- a/.github/workflows/intl4x.yml
+++ b/.github/workflows/intl4x.yml
@@ -120,7 +120,7 @@ jobs:
         cd ffi/dart
         dart pub get
         cd ../..
-        dart run ffi/dart/tool/build_libs.dart bin/linux_x64 linux_x64 dynamic icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,compiled_data
+        dart run ffi/dart/tool/build_libs.dart bin/linux_x64 linux_x64 dynamic icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap,compiled_data
 
     - name: Build Mac
       if: matrix.os == 'macos-latest'
@@ -132,7 +132,7 @@ jobs:
         cd ffi/dart
         dart pub get
         cd ../..
-        dart run ffi/dart/tool/build_libs.dart bin/macos_arm64 macos_arm64 dynamic icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,compiled_data
+        dart run ffi/dart/tool/build_libs.dart bin/macos_arm64 macos_arm64 dynamic icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap,compiled_data
 
     - name: Build Windows
       if: matrix.os == 'windows-latest'
@@ -144,7 +144,7 @@ jobs:
         cd ffi/dart
         dart pub get
         cd ../..
-        dart run ffi/dart/tool/build_libs.dart bin/windows_x64 windows_x64 dynamic icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,compiled_data
+        dart run ffi/dart/tool/build_libs.dart bin/windows_x64 windows_x64 dynamic icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap,compiled_data
 
     - run: echo "LOCAL_ICU4X_BINARY=$(realpath submodules/icu4x/bin/linux_x64)" >> $GITHUB_ENV
       if: matrix.os == 'ubuntu-latest'
diff --git a/.github/workflows/intl4x_artifacts.yml b/.github/workflows/intl4x_artifacts.yml
index d318c0a9..d5a738fe 100644
--- a/.github/workflows/intl4x_artifacts.yml
+++ b/.github/workflows/intl4x_artifacts.yml
@@ -68,14 +68,14 @@ jobs:
         cd ffi/dart
         dart pub get
         cd ../..
-        dart run ffi/dart/tool/build_libs.dart bin/android_arm_${{ matrix.compiletype }} android_arm ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
-        dart run ffi/dart/tool/build_libs.dart bin/android_arm64_${{ matrix.compiletype }} android_arm64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
-        dart run ffi/dart/tool/build_libs.dart bin/android_ia32_${{ matrix.compiletype }} android_ia32 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
-        dart run ffi/dart/tool/build_libs.dart bin/android_x64_${{ matrix.compiletype }} android_x64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
-        dart run ffi/dart/tool/build_libs.dart bin/linux_arm_${{ matrix.compiletype }} linux_arm ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
-        dart run ffi/dart/tool/build_libs.dart bin/linux_arm64_${{ matrix.compiletype }} linux_arm64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
-        dart run ffi/dart/tool/build_libs.dart bin/linux_riscv64_${{ matrix.compiletype }} linux_riscv64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
-        dart run ffi/dart/tool/build_libs.dart bin/linux_x64_${{ matrix.compiletype }} linux_x64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/android_arm_${{ matrix.compiletype }} android_arm ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/android_arm64_${{ matrix.compiletype }} android_arm64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/android_ia32_${{ matrix.compiletype }} android_ia32 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/android_x64_${{ matrix.compiletype }} android_x64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/linux_arm_${{ matrix.compiletype }} linux_arm ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/linux_arm64_${{ matrix.compiletype }} linux_arm64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/linux_riscv64_${{ matrix.compiletype }} linux_riscv64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/linux_x64_${{ matrix.compiletype }} linux_x64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
 
     - name: Build Linux data
       if: matrix.os == 'ubuntu-latest' && matrix.compiletype == 'static'
@@ -105,11 +105,11 @@ jobs:
         cd ffi/dart
         dart pub get
         cd ../..
-        dart run ffi/dart/tool/build_libs.dart bin/ios_arm_${{ matrix.compiletype }} ios_arm ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
-        dart run ffi/dart/tool/build_libs.dart bin/ios_arm64_${{ matrix.compiletype }} ios_arm64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
-        dart run ffi/dart/tool/build_libs.dart bin/ios_x64_${{ matrix.compiletype }} ios_x64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
-        dart run ffi/dart/tool/build_libs.dart bin/macos_arm64_${{ matrix.compiletype }} macos_arm64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
-        dart run ffi/dart/tool/build_libs.dart bin/macos_x64_${{ matrix.compiletype }} macos_x64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/ios_arm_${{ matrix.compiletype }} ios_arm ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/ios_arm64_${{ matrix.compiletype }} ios_arm64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/ios_x64_${{ matrix.compiletype }} ios_x64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/macos_arm64_${{ matrix.compiletype }} macos_arm64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/macos_x64_${{ matrix.compiletype }} macos_x64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
 
     - name: Build Mac data
       if: matrix.os == 'macos-latest' && matrix.compiletype == 'static'
@@ -134,9 +134,9 @@ jobs:
         cd ffi/dart
         dart pub get
         cd ../..
-        dart run ffi/dart/tool/build_libs.dart bin/windows_arm64_${{ matrix.compiletype }} windows_arm64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
-        dart run ffi/dart/tool/build_libs.dart bin/windows_ia32_${{ matrix.compiletype }} windows_ia32 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
-        dart run ffi/dart/tool/build_libs.dart bin/windows_x64_${{ matrix.compiletype }} windows_x64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/windows_arm64_${{ matrix.compiletype }} windows_arm64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/windows_ia32_${{ matrix.compiletype }} windows_ia32 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
+        dart run ffi/dart/tool/build_libs.dart bin/windows_x64_${{ matrix.compiletype }} windows_x64 ${{ matrix.compiletype }} icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,experimental_components,icu_casemap${{ env.DATA }}
 
     - name: Build Windows data
       if: matrix.os == 'windows-latest' && matrix.compiletype == 'static'
diff --git a/pkgs/intl4x/CHANGELOG.md b/pkgs/intl4x/CHANGELOG.md
index 594384b6..29bfb053 100644
--- a/pkgs/intl4x/CHANGELOG.md
+++ b/pkgs/intl4x/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.10.2-wip
+
+- Add case mapping functionality.
+
 ## 0.10.1
 
 - Upgrade to new artifacts.
diff --git a/pkgs/intl4x/hook/build.dart b/pkgs/intl4x/hook/build.dart
index e19792a9..bd8ea94e 100644
--- a/pkgs/intl4x/hook/build.dart
+++ b/pkgs/intl4x/hook/build.dart
@@ -191,21 +191,23 @@ Future<Uri> buildLib(BuildConfig config, String workingDirectory) async {
     }
     final tempDir = await Directory.systemTemp.createTemp();
 
-    final stdFeatures = [
-      'icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals',
+    final commonFeatures = [
+      'icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals,icu_casemap',
       'compiled_data',
       'buffer_provider',
+      'experimental_components',
+    ];
+
+    final stdFeatures = [
+      ...commonFeatures,
       'logging',
       'simple_logger',
-      'experimental_components',
     ];
     final noStdFeatures = [
-      'icu_collator,icu_datetime,icu_list,icu_decimal,icu_plurals',
-      'compiled_data',
-      'buffer_provider',
+      ...commonFeatures,
+      //noStdFeatures
       'libc-alloc',
       'panic-handler',
-      'experimental_components',
     ];
     final linkModeType = config.linkModePreference == LinkModePreference.static
         ? 'staticlib'
diff --git a/pkgs/intl4x/lib/case_mapping.dart b/pkgs/intl4x/lib/case_mapping.dart
new file mode 100644
index 00000000..9853c6ba
--- /dev/null
+++ b/pkgs/intl4x/lib/case_mapping.dart
@@ -0,0 +1,15 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'intl4x.dart';
+
+export 'src/case_mapping/case_mapping.dart';
+export 'src/locale/locale.dart';
+
+extension CaseMappingWithIntl4X on String {
+  String toLocaleLowerCase(Locale locale) =>
+      Intl(locale: locale).caseMapping.toLowerCase(this);
+  String toLocaleUpperCase(Locale locale) =>
+      Intl(locale: locale).caseMapping.toUpperCase(this);
+}
diff --git a/pkgs/intl4x/lib/intl4x.dart b/pkgs/intl4x/lib/intl4x.dart
index 32dc1912..54ecaa81 100644
--- a/pkgs/intl4x/lib/intl4x.dart
+++ b/pkgs/intl4x/lib/intl4x.dart
@@ -5,6 +5,8 @@
 import 'collation.dart';
 import 'display_names.dart';
 import 'number_format.dart';
+import 'src/case_mapping/case_mapping.dart';
+import 'src/case_mapping/case_mapping_impl.dart';
 import 'src/collation/collation_impl.dart';
 import 'src/data.dart';
 import 'src/datetime_format/datetime_format.dart';
@@ -82,6 +84,9 @@ class Intl {
             localeMatcher, ecmaPolicy),
       );
 
+  CaseMapping get caseMapping => CaseMapping(
+      CaseMappingImpl.build(locale, data, localeMatcher, ecmaPolicy));
+
   /// Construct an [Intl] instance providing the current [locale] and the
   /// [ecmaPolicy] defining which locales should fall back to the browser
   /// provided functions.
diff --git a/pkgs/intl4x/lib/src/case_mapping/case_mapping.dart b/pkgs/intl4x/lib/src/case_mapping/case_mapping.dart
new file mode 100644
index 00000000..3f818fcb
--- /dev/null
+++ b/pkgs/intl4x/lib/src/case_mapping/case_mapping.dart
@@ -0,0 +1,33 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import '../test_checker.dart';
+import 'case_mapping_impl.dart';
+
+/// A locale-sensitive case mapper for transforming strings.
+///
+/// This class provides methods to convert strings to lowercase or uppercase
+/// based on the current locale. During testing, the input is returned
+/// unchanged.
+class CaseMapping {
+  final CaseMappingImpl _caseMappingImpl;
+
+  const CaseMapping(this._caseMappingImpl);
+
+  String toLowerCase(String input) {
+    if (isInTest) {
+      return input;
+    } else {
+      return _caseMappingImpl.toLowerCase(input);
+    }
+  }
+
+  String toUpperCase(String input) {
+    if (isInTest) {
+      return input;
+    } else {
+      return _caseMappingImpl.toUpperCase(input);
+    }
+  }
+}
diff --git a/pkgs/intl4x/lib/src/case_mapping/case_mapping_4x.dart b/pkgs/intl4x/lib/src/case_mapping/case_mapping_4x.dart
new file mode 100644
index 00000000..1b8a67a1
--- /dev/null
+++ b/pkgs/intl4x/lib/src/case_mapping/case_mapping_4x.dart
@@ -0,0 +1,32 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import '../bindings/lib.g.dart' as icu;
+import '../data.dart';
+import '../data_4x.dart';
+import '../locale/locale.dart';
+import '../locale/locale_4x.dart';
+import 'case_mapping_impl.dart';
+
+CaseMappingImpl getCaseMapping4X(
+  Locale locale,
+  Data data,
+  Null _,
+) =>
+    CaseMapping4X(locale, data);
+
+class CaseMapping4X extends CaseMappingImpl {
+  final icu.CaseMapper _caseMapper;
+
+  CaseMapping4X(super.locale, Data data)
+      : _caseMapper = icu.CaseMapper(data.to4X());
+
+  @override
+  String toLowerCase(String input) =>
+      _caseMapper.lowercase(input, locale.to4X());
+
+  @override
+  String toUpperCase(String input) =>
+      _caseMapper.uppercase(input, locale.to4X());
+}
diff --git a/pkgs/intl4x/lib/src/case_mapping/case_mapping_ecma.dart b/pkgs/intl4x/lib/src/case_mapping/case_mapping_ecma.dart
new file mode 100644
index 00000000..9cbe01f3
--- /dev/null
+++ b/pkgs/intl4x/lib/src/case_mapping/case_mapping_ecma.dart
@@ -0,0 +1,39 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:js_interop';
+
+import '../locale/locale.dart';
+import '../options.dart';
+import 'case_mapping_impl.dart';
+
+CaseMappingImpl? getCaseMappingECMA(
+  Locale locale,
+  Null __,
+  LocaleMatcher _,
+) =>
+    _CaseMappingECMA.tryToBuild(locale);
+
+extension on JSString {
+  @JS('String.toLocaleUpperCase')
+  external String toLocaleUpperCase(String locale);
+  @JS('String.toLocaleLowerCase')
+  external String toLocaleLowerCase(String locale);
+}
+
+class _CaseMappingECMA extends CaseMappingImpl {
+  _CaseMappingECMA(super.locale);
+
+  static CaseMappingImpl? tryToBuild(
+    Locale locale,
+  ) =>
+      _CaseMappingECMA(locale);
+  @override
+  String toUpperCase(String input) =>
+      input.toJS.toLocaleUpperCase(locale.toLanguageTag());
+
+  @override
+  String toLowerCase(String input) =>
+      input.toJS.toLocaleLowerCase(locale.toLanguageTag());
+}
diff --git a/pkgs/intl4x/lib/src/case_mapping/case_mapping_impl.dart b/pkgs/intl4x/lib/src/case_mapping/case_mapping_impl.dart
new file mode 100644
index 00000000..3fd43b84
--- /dev/null
+++ b/pkgs/intl4x/lib/src/case_mapping/case_mapping_impl.dart
@@ -0,0 +1,40 @@
+// Copyright (c) 2023, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:meta/meta.dart' show ResourceIdentifier;
+
+import '../../ecma_policy.dart';
+import '../data.dart';
+import '../ecma/ecma_policy.dart';
+import '../locale/locale.dart';
+import '../options.dart';
+import '../utils.dart';
+import 'case_mapping_stub.dart' if (dart.library.js) 'case_mapping_ecma.dart';
+import 'case_mapping_stub_4x.dart' if (dart.library.io) 'case_mapping_4x.dart';
+
+abstract class CaseMappingImpl {
+  final Locale locale;
+
+  CaseMappingImpl(this.locale);
+
+  String toLowerCase(String input);
+  String toUpperCase(String input);
+
+  @ResourceIdentifier('CaseMapping')
+  static CaseMappingImpl build(
+    Locale locales,
+    Data data,
+    LocaleMatcher localeMatcher,
+    EcmaPolicy ecmaPolicy,
+  ) =>
+      buildFormatter(
+        locales,
+        data,
+        null,
+        localeMatcher,
+        ecmaPolicy,
+        getCaseMappingECMA,
+        getCaseMapping4X,
+      );
+}
diff --git a/pkgs/intl4x/lib/src/case_mapping/case_mapping_stub.dart b/pkgs/intl4x/lib/src/case_mapping/case_mapping_stub.dart
new file mode 100644
index 00000000..d0e1fb3c
--- /dev/null
+++ b/pkgs/intl4x/lib/src/case_mapping/case_mapping_stub.dart
@@ -0,0 +1,14 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import '../locale/locale.dart';
+import '../options.dart';
+import 'case_mapping_impl.dart';
+
+CaseMappingImpl? getCaseMappingECMA(
+  Locale locale,
+  Null _,
+  LocaleMatcher __,
+) =>
+    throw UnimplementedError('Cannot use ECMA outside of web environments.');
diff --git a/pkgs/intl4x/lib/src/case_mapping/case_mapping_stub_4x.dart b/pkgs/intl4x/lib/src/case_mapping/case_mapping_stub_4x.dart
new file mode 100644
index 00000000..a1f4533f
--- /dev/null
+++ b/pkgs/intl4x/lib/src/case_mapping/case_mapping_stub_4x.dart
@@ -0,0 +1,14 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import '../data.dart';
+import '../locale/locale.dart';
+import 'case_mapping_impl.dart';
+
+CaseMappingImpl getCaseMapping4X(
+  Locale locale,
+  Data data,
+  Null _,
+) =>
+    throw UnimplementedError('Cannot use ICU4X in web environments.');
diff --git a/pkgs/intl4x/pubspec.yaml b/pkgs/intl4x/pubspec.yaml
index e6db3305..b5a35d32 100644
--- a/pkgs/intl4x/pubspec.yaml
+++ b/pkgs/intl4x/pubspec.yaml
@@ -1,7 +1,7 @@
 name: intl4x
 description: >-
   A lightweight modular library for internationalization (i18n) functionality.
-version: 0.10.1
+version: 0.10.2-wip
 repository: https://github.com/dart-lang/i18n/tree/main/pkgs/intl4x
 platforms:
   web:
diff --git a/pkgs/intl4x/test/case_mapping_test.dart b/pkgs/intl4x/test/case_mapping_test.dart
new file mode 100644
index 00000000..0b95ac25
--- /dev/null
+++ b/pkgs/intl4x/test/case_mapping_test.dart
@@ -0,0 +1,25 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:intl4x/case_mapping.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  testWithFormatting('test name', () {
+    const enUS = Locale(language: 'en', region: 'US');
+    expect('İstanbul'.toLocaleLowerCase(enUS), 'i̇stanbul');
+    expect('ALPHABET'.toLocaleLowerCase(enUS), 'alphabet');
+
+    expect('\u0130'.toLocaleLowerCase(const Locale(language: 'tr')), 'i');
+    expect('\u0130'.toLocaleLowerCase(enUS), isNot('i'));
+
+    final locales = ['tr', 'TR', 'tr-TR', 'tr-u-co-search', 'tr-x-turkish']
+        .map(Locale.parse);
+    for (final locale in locales) {
+      expect('\u0130'.toLocaleLowerCase(locale), 'i');
+    }
+  });
+}