Lightweight i18n Solution for Flutter

Lightweight i18n Solution for Flutter

Lightweight i18n Solution for Flutter.Use JSON files to create typesafe translations.



Lightweight i18n solution. Use JSON files to create typesafe translations.

Getting Started

Step 1: Add dependencies

  fast_i18n: ^3.0.3

  build_runner: any

Step 2: Create JSON files

Create these files inside your lib directory. Preferably in one common package like lib/i18n. Only files having the .i18n.json file extension will be detected. You can configure it.

strings.i18n.json (default, fallback)

  "hello": "Hello $name",
  "save": "Save",
  "login": {
    "success": "Logged in successfully",
    "fail": "Logged in failed"


  "hello": "Hallo $name",
  "save": "Speichern",
  "login": {
    "success": "Login erfolgreich",
    "fail": "Login fehlgeschlagen"

Step 3: Generate the dart code

flutter pub run build_runner build

Step 4: Initialize

a) use device locale

void main() {
  WidgetsFlutterBinding.ensureInitialized(); // add this
  LocaleSettings.useDeviceLocale(); // and this

b) use specific locale

void initState() {
  String storedLocale = loadFromStorage(); // your logic here

Step 4a: Override 'supportedLocales'

This is optional but recommended.

Standard flutter controls (e.g. back button's tooltip) will also pick the right locale.

  localizationsDelegates: const [
  supportedLocales: LocaleSettings.supportedLocales, // <---

Step 4b: iOS configuration

File: ios/Runner/Info.plist


Step 5: Use your translations

Text(t.login.success); // plain
Text(t.hello(name: 'Tom')); // with argument
Text(t.step[3]); // with index (for arrays)
Text(t.type['WARNING']); // with key (for maps)

// advanced
TranslationProvider(child: MyApp()); // wrap your app with TranslationProvider
// [...]
final t = Translations.of(context); // forces a rebuild on locale change
String translateAdvanced = t.hello(name: 'Tom');


When the dart code has been generated, you will see some useful classes and functions

t - the translate variable for simple translations

Translations.of(context) - translations which reacts to locale changes

TranslationProvider - App wrapper, used for Translations.of(context)

LocaleSettings.useDeviceLocale() - use the locale of the device

LocaleSettings.setLocale('de') - change the locale

LocaleSettings.setLocaleTyped(AppLocale.en) - change the locale (typed version)

LocaleSettings.currentLocale - get the current locale

LocaleSettings.currentLocaleTyped - get the current locale (typed version)

LocaleSettings.locales - get the supported locales

LocaleSettings.supportedLocales - see step 4a


All settings can be set in the build.yaml file. Place it in the root directory.

          base_locale: en
          input_directory: lib/i18n
          input_file_pattern: .i18n.json
          output_directory: lib/i18n
          output_file_pattern: .g.dart
          translate_var: t
          enum_name: AppLocale
          key_case: snake
            - a
            - b
            - c.d
Key Type Usage Default
base_locale String locale of default json en
input_directory String path to input directory null
input_file_pattern String input file pattern .i18n.json
output_directory String path to output directory null
output_file_pattern String output file pattern .g.dart
translate_var String translate variable name t
enum_name String enum name AppLocale
key_case camel, pascal, snake transform keys (optional) null
maps List<String> entries which should be accessed via keys []


How do I add arguments?

Use the $ prefix.

In edge cases you can also wrap it with ${...}.

  "greeting": "Hello $name",
  "distance": "${distance}m"
t.greeting(name: 'Tom'); // Hello Tom
t.distance(distance: 4.5); // 4.5m

How can I access translations using maps?

Define the maps in your build.yaml. Keep in mind that all nice features like autocompletion are gone.


  "welcome": "Welcome",
  "thisIsAMap": {
    "hello world": "hello"
  "classicClass": {
    "hello": "hello",
    "aMapInClass": {
      "hi": "hi"


            - thisIsAMap
            - classicClass.aMapInClass

Now you can access the translations via keys:

String a = t.thisIsAMap['hello world'];
String b = t.classicClass.hello; // the "classical" way
String c = t.classicClass.aMapInClass['hi']; // nested

Can I use lists?

Lists are fully supported. You can also put lists or maps inside lists!

  "niceList": [
      "first item in nested list",
      "second item in nested list"
      "wow": "WOW!",
      "ok": "OK!"
      "a map entry": "access via key",
      "another entry": "access via second key"
String a = t.niceList[1]; // "nice"
String b = t.niceList[2][0]; // "first item in nested list"
String c = t.niceList[3].ok; // "OK!"
String d = t.niceList[4]['a map entry']; // "access via key"

Download Details:

Author: Tienisto Download Link: Download The Source Code Official Website: License: MIT License

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