added support for overriding locales

app/lib/features/user/data/models/engine_settings.dart

@@ -21,6 +21,7 @@ import 'dart:convert';
 
 import 'package:copy_with_extension/copy_with_extension.dart';
 import 'package:fast_equatable/fast_equatable.dart';
+import 'package:flutter/widgets.dart';
 import 'package:flutter_mozilla_components/flutter_mozilla_components.dart';
 import 'package:json_annotation/json_annotation.dart';
 import 'package:nullability/nullability.dart';
@@ -75,6 +76,9 @@ class EngineSettings extends GeckoEngineSettings with FastEquatable {
   @override
   bool get enterpriseRootsEnabled => super.enterpriseRootsEnabled!;
 
+  @override
+  List<String> get locales => super.locales!;
+
   final QueryParameterStripping queryParameterStripping;
 
   final BounceTrackingProtectionMode bounceTrackingProtectionMode;
@@ -130,6 +134,7 @@ class EngineSettings extends GeckoEngineSettings with FastEquatable {
     required this.dohExceptionsList,
     required super.fingerprintingProtectionOverrides,
     required this.enablePdfJs,
+    required super.locales,
   });
 
   EngineSettings.withDefaults({
@@ -154,6 +159,7 @@ class EngineSettings extends GeckoEngineSettings with FastEquatable {
     List<String>? dohExceptionsList,
     String? fingerprintingProtectionOverrides,
     bool? enablePdfJs,
+    List<String>? locales,
   }) : queryParameterStripping =
            queryParameterStripping ?? QueryParameterStripping.disabled,
        bounceTrackingProtectionMode =
@@ -188,6 +194,11 @@ class EngineSettings extends GeckoEngineSettings with FastEquatable {
          fingerprintingProtectionOverrides:
              fingerprintingProtectionOverrides ??
              FingerprintOverrides.defaults().toString(),
+         locales:
+             locales ??
+             WidgetsBinding.instance.platformDispatcher.locales
+                 .map((x) => x.toLanguageTag())
+                 .toList(),
        );
 
   static AddonCollection? _addonCollectionFromJson(String? json) =>
@@ -226,5 +237,6 @@ class EngineSettings extends GeckoEngineSettings with FastEquatable {
     dohExceptionsList,
     fingerprintingProtectionOverrides,
     enablePdfJs,
+    locales,
   ];
 }

app/lib/features/user/data/models/engine_settings.g.dart

@@ -67,6 +67,8 @@ abstract class _$EngineSettingsCWProxy {
 
   EngineSettings enablePdfJs(bool enablePdfJs);
 
+  EngineSettings locales(List<String>? locales);
+
   /// Creates a new instance with the provided field values.
   /// Passing `null` to a nullable field nullifies it, while `null` for a non-nullable field is ignored. To update a single field use `EngineSettings(...).copyWith.fieldName(value)`.
   ///
@@ -96,6 +98,7 @@ abstract class _$EngineSettingsCWProxy {
     List<String> dohExceptionsList,
     String? fingerprintingProtectionOverrides,
     bool enablePdfJs,
+    List<String>? locales,
   });
 }
 
@@ -207,6 +210,9 @@ class _$EngineSettingsCWProxyImpl implements _$EngineSettingsCWProxy {
   EngineSettings enablePdfJs(bool enablePdfJs) =>
       call(enablePdfJs: enablePdfJs);
 
+  @override
+  EngineSettings locales(List<String>? locales) => call(locales: locales);
+
   @override
   /// Creates a new instance with the provided field values.
   /// Passing `null` to a nullable field nullifies it, while `null` for a non-nullable field is ignored. To update a single field use `EngineSettings(...).copyWith.fieldName(value)`.
@@ -239,6 +245,7 @@ class _$EngineSettingsCWProxyImpl implements _$EngineSettingsCWProxy {
     Object? dohExceptionsList = const $CopyWithPlaceholder(),
     Object? fingerprintingProtectionOverrides = const $CopyWithPlaceholder(),
     Object? enablePdfJs = const $CopyWithPlaceholder(),
+    Object? locales = const $CopyWithPlaceholder(),
   }) {
     return EngineSettings(
       javascriptEnabled: javascriptEnabled == const $CopyWithPlaceholder()
@@ -350,6 +357,10 @@ class _$EngineSettingsCWProxyImpl implements _$EngineSettingsCWProxy {
           ? _value.enablePdfJs
           // ignore: cast_nullable_to_non_nullable
           : enablePdfJs as bool,
+      locales: locales == const $CopyWithPlaceholder()
+          ? _value.locales
+          // ignore: cast_nullable_to_non_nullable
+          : locales as List<String>?,
     );
   }
 }
@@ -422,6 +433,9 @@ EngineSettings _$EngineSettingsFromJson(Map<String, dynamic> json) =>
       fingerprintingProtectionOverrides:
           json['fingerprintingProtectionOverrides'] as String?,
       enablePdfJs: json['enablePdfJs'] as bool?,
+      locales: (json['locales'] as List<dynamic>?)
+          ?.map((e) => e as String)
+          .toList(),
     );
 
 Map<String, dynamic> _$EngineSettingsToJson(
@@ -448,6 +462,7 @@ Map<String, dynamic> _$EngineSettingsToJson(
       _$WebContentIsolationStrategyEnumMap[instance
           .webContentIsolationStrategy]!,
   'enterpriseRootsEnabled': instance.enterpriseRootsEnabled,
+  'locales': instance.locales,
   'queryParameterStripping':
       _$QueryParameterStrippingEnumMap[instance.queryParameterStripping]!,
   'bounceTrackingProtectionMode':