fast_i18n #

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

For Flutter Web users: version 3.0.4 contains the workaround for #79555. Version 4.x.x is web compatible as soon as the Flutter team merge this fix into the stable branch.

About this library #

• 🚀 Minimal setup, create JSON files and get started! No configuration needed.
• 📦 Self-contained, you can remove this library after generation.
• 🐞 Bug-resistant, no typos or missing arguments possible due to compiler errors.
• ⚡ Fast, you get translations using native dart method calls, zero parsing!
• 🔨 Configurable, English is not the default language? Configure it in build.yaml!

You can see an example of the generated file here.

Table of Contents #

• Getting Started
• Configuration
• API
• Features
  • String Interpolation
  • Pluralization
  • Maps
  • Lists
• FAQ

Getting Started #

Step 1: Add dependencies

It is recommended to add fast_i18n to dev_dependencies.

dev_dependencies:
  build_runner: any
  fast_i18n: 4.5.0

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. The part after the underscore _ is the actual locale (e.g. en_US, en-US, fr). You must provide the default translation file (the file without locale extension).

strings.i18n.json (mandatory, 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 fast_i18n

alternative (but slower):

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

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.setLocaleRaw(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

import 'package:my_app/i18n/strings.g.dart'; // import

String a = t.login.success; // plain
String b = t.hello(name: 'Tom'); // with argument
String c = t.step[3]; // with index (for arrays)
String d = 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');

Configuration #

This is optional. This library works without any configuration (in most cases).

For customization, you can create the build.yaml file. Place it in the root directory.

targets:
  $default:
    builders:
      fast_i18n:i18nBuilder:
        options:
          null_safety: true
          base_locale: fr
          input_directory: lib/i18n
          input_file_pattern: .i18n.json
          output_directory: lib/i18n
          output_file_pattern: .g.dart
          translate_var: t
          enum_name: AppLocale
          translation_class_visibility: private
          key_case: snake
          maps:
            - error.codes
            - category
            - iconNames
          pluralization:
            cardinal:
              - someKey.apple
            ordinal:
              - someKey.place

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(AppLocale.en) - change the locale

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

LocaleSettings.currentLocale - get the current locale

LocaleSettings.baseLocale - get the base locale

LocaleSettings.supportedLocalesRaw - get the supported locales

LocaleSettings.supportedLocales - see step 4a

LocaleSettings.setPluralResolver - set pluralization resolver for unsupported languages

Features #

String Interpolation #

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

Pluralization #

This library uses the concept defined here.

Some languages have support out of the box. See here.

In order to use plurals, please add the key paths to build.yaml. Next, add the required quantities to the translation file. You can access the num count but it is optional.

strings.i18n.json

{
  "someKey": {
    "apple": {
      "one": "I have $count apple.",
      "other": "I have $count apples."
    },
    "place": {
      "one": "${count}st place.",
      "two": "${count}nd place.",
      "few": "${count}rd place.",
      "other": "${count}th place."
    }
  }
}

build.yaml

targets:
  $default:
    builders:
      fast_i18n:i18nBuilder:
        options:
          pluralization:
            cardinal:
              - someKey.apple
            ordinal:
              - someKey.place

Now you can access them.

String a = t.someKey.apple(count: 1); // I have 1 apple.
String b = t.someKey.apple(count: 2); // I have 2 apples.

In case your language is not supported, you must provide a custom pluralization resolver:

// add this before you call the pluralization strings. Otherwise an exception will be thrown.
LocaleSettings.setPluralResolver(
  language: 'en',
  cardinalResolver: (num n, {String? zero, String? one, String? two, String? few, String? many, String? other}) {
    if (n == 1)
      return one!;
    return other!;
  },
  ordinalResolver: (num n, {String? zero, String? one, String? two, String? few, String? many, String? other}) {
    if (n % 10 == 1 && n % 100 != 11)
      return one!;
    if (n % 10 == 2 && n % 100 != 12)
      return two!;
    if (n % 10 == 3 && n % 100 != 13)
      return few!;
    return other!;
  },
);

Maps #

You can access each translation via string keys by defining maps.

Define the maps in your build.yaml. Each configuration item represents the translation tree separated by dots.

Keep in mind that all nice features like autocompletion are gone.

strings.i18n.json

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

build.yaml

targets:
  $default:
    builders:
      fast_i18n:i18nBuilder:
        options:
          maps:
            - thisIsAMap
            - notAMapParent.aMapInClass

Now you can access the translations via keys:

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

Lists #

Lists are fully supported. No configuration needed. 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"

FAQ #

Can I write the json files in the asset folder?

Yes. Specify input_directory and output_directory in build.yaml.

targets:
  $default:
    builders:
      fast_i18n:i18nBuilder:
        options:
          input_directory: assets/i18n
          output_directory: lib/i18n

Why setLocale doesn't work?

In most cases you forgot the setState call.

A more elegant solution is to use TranslationProvider(child: MyApp()) and then get you translation variable with final t = Translations.of(context). It will automatically trigger a rebuild on setLocale for all affected widgets.

License #

MIT License

Copyright (c) 2020-2021 Tien Do Nam

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.