Lightweight i18n solution for Flutter

fast_i18n

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

Getting Started

Step 1: Add dependencies

dependencies:
  fast_i18n: ^3.0.2

dev_dependencies:
  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"
  }
}

strings_de.i18n.json

{
  "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
  runApp(MyApp());
}

b) use specific locale

@override
void initState() {
  super.initState();
  String storedLocale = loadFromStorage(); // your logic here
  LocaleSettings.setLocale(storedLocale);
}

Step 4a: Override 'supportedLocales'

This is optional but recommended.

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

MaterialApp(
  localizationsDelegates: const [
    GlobalMaterialLocalizations.delegate,
    GlobalWidgetsLocalizations.delegate,
    GlobalCupertinoLocalizations.delegate,
  ],
  supportedLocales: LocaleSettings.supportedLocales, // <---
)

Step 4b: iOS configuration

File: ios/Runner/Info.plist

<key>CFBundleLocalizations</key>
<array>
   <string>en</string>
   <string>de</string>
</array>

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');

API

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

Configuration

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

targets:
  $default:
    builders:
      fast_i18n:i18nBuilder:
        options:
          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
          maps:
            - 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	[]

FAQ

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.

strings.i18n.json

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

build.yaml

targets:
  $default:
    builders:
      fast_i18n:i18nBuilder:
        options:
          maps:
            - 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": [
    "hello",
    "nice",
    [
      "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"

GitHub

https://github.com/Tienisto/flutter-fast-i18n