internationalization

internationalization

A Flutter package that makes adding multi-language support to your app simple and flexible — no code generation required.

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Features

• ✅ Load translations from local JSON asset files
• ✅ Inject translations at runtime from any external source (API, database, etc.)
• ✅ Nested keys — navigate deep JSON structures with parent or dot notation
• ✅ String interpolation with positional ({0}, {1}) and named (::key::) arguments
• ✅ Plural support — zero, one, other forms
• ✅ Extension methods on String and BuildContext for ergonomic usage
• ✅ TextIntl widget — a drop-in replacement for Text that auto-translates
• ✅ Re-exports NumberFormat and DateFormat from the intl package

---

Installation

dependencies:
  internationalization: ^5.0.1
  flutter_localizations:
    sdk: flutter

---

Setup

1. Asset files

Create one JSON file per language inside your assets folder. The default path is assets/translations/. Files must be named after the language code (e.g. en.json, pt.json).

assets/
└── translations/
    ├── en.json
    ├── pt.json
    └── es.json

Register the folder in pubspec.yaml:

flutter:
  uses-material-design: true
  assets:
    - assets/translations/en.json
    - assets/translations/pt.json
    - assets/translations/es.json

Note: If your translations span multiple files per locale, list every file individually or use a directory entry (e.g. assets/translations/en/). The path must match exactly what you pass to translationsPath.

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2. MaterialApp configuration

import 'package:flutter_localizations/flutter_localizations.dart';
import 'package:internationalization/internationalization.dart';

const _supportedLocales = [
  Locale('en'),
  Locale('pt'),
  Locale('es'),
];

MaterialApp(
  supportedLocales: _supportedLocales,
  localizationsDelegates: [
    InternationalizationDelegate(
      suportedLocales: _supportedLocales,
      // Default path is 'assets/translations/' — only override if needed.
      translationsPath: 'assets/translations/',
      // Optional: merge translations fetched at runtime (API, remote config, etc.)
      addTranslations: (locale) async {
        return {
          'remote_key': 'Value from the network for ${locale.languageCode}',
        };
      },
    ),
    GlobalMaterialLocalizations.delegate,
    GlobalWidgetsLocalizations.delegate,
    GlobalCupertinoLocalizations.delegate,
  ],
);

InternationalizationDelegate parameters

Parameter	Type	Required	Default	Description
suportedLocales	List<Locale>	✅	—	Locales the app supports
translationsPath	String		'assets/translations/'	Path to the JSON files directory
addTranslations	Future<Map<String, dynamic>> Function(Locale)?		null	Callback to inject extra translations at load time

---

JSON structure

Translations are plain JSON objects. Keys can be flat or deeply nested:

{
  "greeting": "Hello, World!",
  "nav": {
    "home": "Home",
    "settings": "Settings"
  },
  "user": {
    "profile": {
      "title": "My Profile"
    }
  }
}

---

Translate

Context extension

// Flat key
context.translate('greeting');

// Nested key — dot notation (shorthand)
context.translate('nav.home');

// Nested key — explicit parent list
context.translate('title', parent: ['user', 'profile']);

String extension

'greeting'.translate(context);

'nav.home'.translate(context);

TextIntl widget

A drop-in replacement for Text that translates its key automatically:

TextIntl('greeting')

TextIntl(
  'nav.home',
  style: TextStyle(fontSize: 18, fontWeight: FontWeight.bold),
)

TextIntl accepts all the same parameters as Text (style, textAlign, overflow, maxLines, etc.) plus the translation parameters parent, args, namedArgs, and pluralValue.

---

Interpolation

Positional arguments — {0}, {1}, …

JSON:

{
  "welcome_message": "Hello, {0}! You have {1} new messages."
}

Dart:

context.translate(
  'welcome_message',
  args: ['Alice', '5'],
);
// → "Hello, Alice! You have 5 new messages."

Named arguments — ::key::

JSON:

{
  "welcome_back": "Welcome back, ::firstName:: ::lastName::!"
}

Dart:

context.translate(
  'welcome_back',
  namedArgs: {'firstName': 'John', 'lastName': 'Doe'},
);
// → "Welcome back, John Doe!"

Combined positional + named

JSON:

{
  "order_ready": "Dear ::name::, your order #{0} is ready."
}

Dart:

context.translate(
  'order_ready',
  args: ['42'],
  namedArgs: {'name': 'Maria'},
);
// → "Dear Maria, your order #42 is ready."

---

Plurals

Define a zero, one, and other form for any key:

JSON:

{
  "cart": {
    "items": {
      "zero": "Your cart is empty.",
      "one": "You have {0} item in your cart.",
      "other": "You have {0} items in your cart."
    }
  }
}

Dart:

// zero
context.translate('items', parent: ['cart'], pluralValue: 0, args: ['0']);
// → "Your cart is empty."

// one
context.translate('items', parent: ['cart'], pluralValue: 1, args: ['1']);
// → "You have 1 item in your cart."

// other
context.translate('items', parent: ['cart'], pluralValue: 42, args: ['42']);
// → "You have 42 items in your cart."

Plural forms can also be combined with named args:

context.translate(
  'download_status',
  parent: ['files'],
  pluralValue: 1,
  namedArgs: {'file': 'report.pdf'},
);

---

NumberFormat & DateFormat

NumberFormat and DateFormat are re-exported directly from the intl package — no extra import needed:

import 'package:internationalization/internationalization.dart';

// Currency
NumberFormat.currency(locale: 'pt_BR', symbol: 'R\$').format(1234.56);
// → "R$ 1.234,56"

// Compact
NumberFormat.compact().format(1200000);
// → "1.2M"

// Date
DateFormat.yMMMMd('en').format(DateTime.now());
// → "April 7, 2026"

DateFormat('EEEE, MMM d yyyy', 'pt').format(DateTime.now());
// → "segunda-feira, abr 7 2026"

See the full docs:

• NumberFormat
• DateFormat

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Runtime translation injection

Use addTranslations to merge extra keys when the delegate loads — useful for remote config, A/B testing, or server-driven copy:

InternationalizationDelegate(
  suportedLocales: _supportedLocales,
  addTranslations: (locale) async {
    final response = await http.get(
      Uri.parse('https://api.example.com/strings/${locale.languageCode}'),
    );
    return jsonDecode(response.body) as Map<String, dynamic>;
  },
),

Injected keys follow the same JSON structure and can be accessed with context.translate, the String extension, or TextIntl exactly like local keys.

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Example

A full showcase example demonstrating every feature is available in the example/ directory. It covers simple strings, nested keys, interpolation, plurals, runtime injection, and NumberFormat/DateFormat — with a live language switcher between English, Portuguese, and Spanish.

cd example
flutter run

---

API reference

Translator

Method	Description
Translator.of(context)	Returns the Translator instance for the current locale
translate(key, {parent, pluralValue, args, namedArgs})	Core translation method
addExternalTranslations(Map)	Merge additional translations at runtime

InternationalizationDelegate

Flutter LocalizationsDelegate<Translator> — wire it into localizationsDelegates.

Extensions

Extension	Method	Description
StringExtension	'key'.translate(context, {...})	Translate from a String literal
ContextTranslator	context.translate('key', {...})	Translate using a BuildContext
ContextTranslator	context.translator	Access the raw Translator instance

TextIntl

A StatelessWidget wrapping Text. Accepts all Text parameters plus parent, args, namedArgs, and pluralValue.