A demonstration of using Riverpod for dynamic locale switching in-app, with persistence.

How It Works

• Fallback Locale: Declared inside locale_state.dart, and set with the @Default decorator.
• Default Locale: At startup, gets the system’s Platform.localeName (via dart:io) and uses it to set the app’s locale.
  • If the platform locale does not match a supported locale
    • The first matching language code locale will be set.
    • Otherwise, the fallback locale will be used.
• Supported Locales: These are stored in a provider, accessible from anywhere. Update this list to add more locales.
• Current Locale: Accessible from a provider anywhere the ref object is available. Watch this provider to rebuild whenever the locale changes. You can still use Localizations.localeOf(context) to get the Locale.

Locale Changes

• initState sets the initial locale from the platform.
  • App starts up with fallback locale
  • initState immediately attempts to restore a locale from persistent storage to Riverpod state.
  • If there is no locale in storage, attempts to use the Platform’s locale.
• The drop down button can be used to select a new locale.
  • This updates state and saves the locale to persistent storage.
• The MaterialApp() is wrapped in a Riverpod ConsumerWidget which will rebuild automatically anytime the watched ref.watch() locale value changes.
• All translated strings are rebuilt as part of this process.

Platform Locale

The Platform.locale property of dart:io library only works on mobile. For web, we need to use dart:html‘s window.navigator.language. This is implemented with the PlatformLocale() interface and conditional imports.

Dependencies

• State Management: Riverpod
• Immutable State: Freezed
  • Notice the custom converter used for saving Locale toJson and fromJson. Freezed works with json_serializable naturally.
• Internationalization / Localization: flutter_localizations
• Persistence: shared_preferences

Getting Started

Code Generator: This app uses build_runner to generate code for freezed.

# flutter pub run build_runner build --delete-conflicting-outputs

Download source code on GitHub

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