Flutter API Reference — Better I18N

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BetterI18nProvider
Props
BuildContext Extensions
BetterI18nController
Constructor
Getters
Methods
I18nCore
Methods
BetterI18nScope
Static Methods
Types
Storage
Testing Utilities

Complete API reference for the better_i18n Flutter/Dart SDK.

BetterI18nProvider #

The top-level widget. Manages the BetterI18nController lifecycle and provides translations to all descendant widgets via BetterI18nScope.

Dart

BetterI18nProvider(
  projectId: 'acme/app',
  defaultLocale: 'en',
  storage: SharedPrefsStorage(),
  loadingBuilder: (_) => const CircularProgressIndicator(),
  child: const MyApp(),
)

Props #

Prop	Type	Required	Default	Description
`projectId`	`String`	Yes	—	Project ID — `"org/project"` slug or canonical UUID
`defaultLocale`	`String`	Yes	—	Fallback locale used when no locale is set
`child`	`Widget`	Yes	—	Root widget of your app
`locale`	`String?`	No	`null`	Externally controlled locale (e.g., from a Cubit/BLoC)
`cdnBaseUrl`	`String?`	No	`https://cdn.better-i18n.com`	CDN URL override
`ttl`	`int?`	No	`300000`	Memory cache TTL in milliseconds (5 min)
`timeout`	`int?`	No	`10000`	CDN fetch timeout in milliseconds
`retry`	`int?`	No	`1`	Number of retry attempts on CDN failure
`storage`	`TranslationStorage?`	No	`null`	Persistent storage adapter — use `SharedPrefsStorage()`
`staticData`	`Map<String, Messages>?`	No	`null`	Bundled fallback translations for airplane mode first launch
`loadingBuilder`	`WidgetBuilder?`	No	`null`	Widget shown while translations are loading (initial load only)
`errorBuilder`	`Widget Function(BuildContext, Object)?`	No	`null`	Widget shown when a fatal error occurs

BuildContext Extensions #

Available on any BuildContext below BetterI18nProvider in the widget tree.

Translate a key with optional interpolation arguments.

Dart

// Simple key
Text(context.t('common.welcome'))

// With interpolation
Text(context.t('common.greeting', args: {'name': 'Osman'}))
// → "Hello, Osman!" (if translation is "Hello, {{name}}!")

Parameters:

Parameter	Type	Required	Description
`key`	`String`	Yes	Key in `"namespace.key"` format
`args`	`Map<String, dynamic>?`	No	Interpolation arguments

Returns: String — Translated text, or the key itself if not found.

Key format: "namespace.key" (e.g., "common.hello", "auth.loginButton"). The part before the first . is the namespace; the rest is the key within that namespace.

Returns the current active locale code.

Dart

final locale = context.i18nLocale;
// → "en", "tr", "de", etc.

Returns: String

Returns the list of available languages from the CDN manifest.

Dart

final languages = context.i18nLanguages;
// → [LanguageOption(code: 'en', name: 'English', ...), ...]

Returns: List<LanguageOption>

Switch to a new locale. Fetches translations from CDN (or cache) and triggers a widget rebuild.

Dart

await context.setI18nLocale('tr');

Parameters:

Parameter	Type	Required	Description
`code`	`String`	Yes	Locale code (e.g., `"tr"`, `"de"`)

Returns: Future<void>

Direct access to the BetterI18nController. Use for advanced scenarios.

Dart

final controller = context.i18n;
final isReady = controller.isReady;
final messages = controller.messages;

Returns: BetterI18nController

BetterI18nController #

Manages i18n state — locale, messages, and languages. Extends ChangeNotifier so widgets rebuild when state changes.

Dart

final controller = BetterI18nController(
  config: const I18nConfig(
    projectId: 'acme/app',
    defaultLocale: 'en',
  ),
  initialLocale: 'tr',
);
await controller.initialize();

Constructor #

Parameter	Type	Required	Description
`config`	`I18nConfig`	Yes	Core configuration
`initialLocale`	`String?`	No	Starting locale — defaults to `config.defaultLocale`

Getters #

Getter	Type	Description
`locale`	`String`	Current active locale
`messages`	`Messages?`	Loaded translation messages (`null` until ready)
`languages`	`List<LanguageOption>`	Available languages from CDN manifest
`isLoading`	`bool`	Whether translations are currently loading
`isReady`	`bool`	Whether the controller is initialized and ready
`error`	`Object?`	Last error that occurred during loading, if any

Methods #

Fetches the CDN manifest and initial locale messages in parallel. Called automatically by BetterI18nProvider — only call manually when using BetterI18nController directly.

Dart

await controller.initialize();

Returns: Future<void>

Switch to a new locale and reload messages.

Dart

await controller.setLocale('tr');

Returns: Future<void>

Translate a key with optional interpolation arguments. Returns the key itself if not found.

Dart

final text = controller.translate('common.welcome', args: {'name': 'Osman'});

Returns: String

I18nCore #

The pure Dart core engine — no Flutter dependency. Implements the 4-tier fallback chain. Used internally by BetterI18nController.

Dart

final core = I18nCore(
  config: NormalizedConfig(
    projectId: 'acme/app',
    defaultLocale: 'en',
    cdnBaseUrl: 'https://cdn.better-i18n.com',
    manifestCacheTtlMs: 300000,
    timeout: 10000,
    retry: 1,
  ),
);

Methods #

Fetch the CDN manifest with full fallback chain (memory → CDN → storage).

Dart

final manifest = await core.getManifest();
final manifest = await core.getManifest(forceRefresh: true);

Returns: Future<ManifestResponse>

Fetch translation messages for a locale with full fallback chain.

Dart

final messages = await core.getMessages('tr');

Returns: Future<Messages>

Get available languages as LanguageOption list.

Dart

final languages = await core.getLanguages();

Returns: Future<List<LanguageOption>>

Get available locale codes.

Dart

final locales = await core.getLocales();
// → ["en", "tr", "de"]

Returns: Future<List<String>>

Clear all static caches — manifest and messages. Useful between tests.

Dart

I18nCore.clearAllCaches();

Also available as separate methods:

Dart

I18nCore.clearManifestCache();
I18nCore.clearMessagesCache();

BetterI18nScope #

Low-level InheritedNotifier that provides BetterI18nController to the widget tree. Used internally by BetterI18nProvider — use directly only for testing or advanced scenarios.

Dart

BetterI18nScope(
  controller: myController,
  child: MyWidget(),
)

Static Methods #

Look up the nearest BetterI18nController in the widget tree.

Dart

final controller = BetterI18nScope.of(context);

Returns: BetterI18nController

Throws if no BetterI18nScope is found in the ancestor tree.

Types #

Simplified language info for UI components (e.g., language picker).

Dart

class LanguageOption {
  final String code;          // "en", "tr"
  final String? name;         // "English", "Turkish" (English name)
  final String? nativeName;   // "English", "Türkçe" (native name)
  final String? flagUrl;      // URL to flag image (from dashboard)
  final bool isDefault;       // true for the source/default language
}

Translation messages keyed by namespace, then by key.

Dart

typedef Messages = Map<String, Map<String, dynamic>>;

// Example:
// {
//   "common": {"welcome": "Welcome", "appTitle": "My App"},
//   "auth": {"loginButton": "Sign In"},
// }

Matches the CDN response format exactly.

Abstract interface for persistent storage adapters.

Dart

abstract class TranslationStorage {
  Future<String?> get(String key);
  Future<void> set(String key, String value);
  Future<void> remove(String key);
}

Implement this class to use a custom storage backend (SQLite, Hive, secure storage, etc.).

Core configuration class passed to BetterI18nController.

Dart

const I18nConfig({
  required String project,       // "org/project"
  required String defaultLocale, // "en"
  String? cdnBaseUrl,            // CDN URL override
  int? ttl,                      // memory cache TTL (ms)
  int? timeout,                  // fetch timeout (ms)
  int? retry,                    // retry count
  TranslationStorage? storage,   // persistent storage
  Map<String, Messages>? staticData, // bundled fallback
})

CDN manifest data returned by I18nCore.getManifest().

Dart

class ManifestResponse {
  final List<ManifestLanguage> languages;
  final String? projectSlug;
  final String? sourceLanguage;
  final String? updatedAt;
}

Raw language info from the CDN manifest.

Dart

class ManifestLanguage {
  final String code;
  final String? name;
  final String? nativeName;
  final String? flagUrl;
  final bool isSource; // true for source language
}

Storage #

Persistent storage adapter backed by shared_preferences. The recommended choice for production Flutter apps.

Dart

import 'package:better_i18n/better_i18n.dart';

BetterI18nProvider(
  projectId: 'acme/app',
  defaultLocale: 'en',
  storage: SharedPrefsStorage(),
  child: const MyApp(),
)

Requires the shared_preferences package in pubspec.yaml.

Testing Utilities #

Inject a pre-configured controller directly into the widget tree — no CDN calls needed:

Dart

import 'package:better_i18n/better_i18n.dart';
import 'package:flutter_test/flutter_test.dart';

testWidgets('renders translated welcome text', (tester) async {
  // Clear static caches between tests
  I18nCore.clearAllCaches();

  final controller = BetterI18nController(
    config: const I18nConfig(
      projectId: 'test/app',
      defaultLocale: 'en',
      staticData: {
        'en': {
          'common': {
            'welcome': 'Welcome',
            'greeting': 'Hello, {{name}}!',
          },
        },
      },
    ),
  );
  await controller.initialize();

  await tester.pumpWidget(
    BetterI18nScope(
      controller: controller,
      child: Builder(
        builder: (ctx) => MaterialApp(
          home: Scaffold(
            body: Text(ctx.t('common.welcome')),
          ),
        ),
      ),
    ),
  );

  expect(find.text('Welcome'), findsOneWidget);
});

Static method to clear all in-memory caches between tests. Essential when multiple tests share the same project identifier.

Dart

setUp(() {
  I18nCore.clearAllCaches();
});

Clears both manifest and messages caches. Also available as:

I18nCore.clearManifestCache() — manifest only
I18nCore.clearMessagesCache() — messages only