fast_i18n #

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

For legacy users: version 4.x.x-legacy is built on build 1.3.0, glob 1.2.0, yaml 2.2.1 and build_runner 1.10.2. This way, you can access the latest features in your legacy project.

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.

This is how you access the translations:

final t = Translations.of(context); // optional, there is also a static getter without context

String a = t.mainScreen.title;                         // simple use case
String b = t.game.end.highscore(score: 32.6);          // with parameters
String c = t.items(count: 2);                          // with pluralization (using count)
String d = t.greet(name: 'Tom', context: Gender.male); // with custom context
String e = t.intro.step[4];                            // with index
String f = t.error.type['WARNING'];                    // with dynamic key
String g = t['mainScreen.title'];                      // with fully dynamic key

Table of Contents #

• Getting Started
• Configuration
• Features
  • Auto Rebuild
  • String Interpolation
  • Linked Translations
  • Locale Enum
  • Pluralization
  • Custom Contexts
  • Maps
  • Dynamic Keys
  • Lists
  • Fallback
• API
• FAQ

Getting Started #

Step 1: Add dependencies

It is recommended to add fast_i18n to dev_dependencies.

dev_dependencies:
  build_runner: any
  fast_i18n: 5.0.0

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).

// File: strings.i18n.json (mandatory, default, fallback)
{
  "hello": "Hello $name",
  "save": "Save",
  "login": {
    "success": "Logged in successfully",
    "fail": "Logged in failed"
  }
}

// File: 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.

# File: pubspec.yaml
dependencies:
  flutter:
    sdk: flutter
  flutter_localizations: # add this
    sdk: flutter

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; // get translation

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:
        options:
          base_locale: fr
          fallback_strategy: base_locale
          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
          string_interpolation: double_braces
          flat_map: false
          maps:
            - error.codes
            - category
            - iconNames
          pluralization:
            auto: cardinal
            cardinal:
              - someKey.apple
            ordinal:
              - someKey.place
          contexts:
            gender_context:
              enum:
                - male
                - female
              auto: false
              paths:
                - my.path.to.greet

Features #

Auto Rebuild #

You can let the library rebuild automatically for you. The watch function from build_runner is NOT maintained.

Just run this command:

flutter pub run fast_i18n watch

String Interpolation #

There are three modes configurable via string_interpolation in build.yaml.

You can always escape them by adding a backslash, e.g. \{notAnArgument}.

Linked Translations #

You can link one translation to another. Add the prefix @: followed by the translation key.

{
  "meta": {
    "appName": "My App"
  },
  "welcome": "Welcome to @:meta.appName"
}

Locale Enum #

Typesafety is one of the main advantages of this library. No typos. Enjoy exhausted switch-cases!

// this enum is generated automatically for you
enum AppLocale {
  en,
  fr,
  zhCn,
}

// use cases
LocaleSettings.setLocale(AppLocale.en); // set locale
List<AppLocale> locales = AppLocale.values; // list all supported locales
Locale locale = AppLocale.en.flutterLocale; // convert to native flutter locale
String tag = AppLocale.en.languageTag; // convert to string tag (e.g. en-US)
final t = AppLocale.en.translations; // get translations of one locale

Pluralization #

This library uses the concept defined here.

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

Plurals are detected by the following keywords: zero, one, two, few, many, other.

You can access the num count but it is optional.

// File: strings.i18n.json
{
  "someKey": {
    "apple": {
      "one": "I have $count apple.",
      "other": "I have $count apples."
    }
  }
}

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

Plurals are interpreted as cardinals by default. You can configure or disable it.

// File: 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."
    }
  }
}

# File: build.yaml
targets:
  $default:
    builders:
      fast_i18n:
        options:
          pluralization:
            auto: off
            cardinal:
              - someKey.apple
            ordinal:
              - someKey.place

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.
// you don't need to specify both
LocaleSettings.setPluralResolver(
  language: 'en',
  cardinalResolver: (num n, {String? zero, String? one, String? two, String? few, String? many, String? other}) {
    if (n == 0)
      return zero ?? other!;
    if (n == 1)
      return one ?? other!;
    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 ?? other!;
    if (n % 10 == 2 && n % 100 != 12)
      return two ?? other!;
    if (n % 10 == 3 && n % 100 != 13)
      return few ?? other!;
    return other!;
  },
);

Custom Contexts #

You can utilize custom contexts to differentiate between male and female forms.

// File: strings.i18n.json
{
  "greet": {
    "male": "Hello Mr $name",
    "female": "Hello Ms $name"
  }
}

# File: build.yaml
targets:
  $default:
    builders:
      fast_i18n:
        options:
          contexts:
            gender_context:
              enum:
                - male
                - female
            polite_context:
              enum:
                - polite
                - rude

String a = t.greet(name: 'Maria', context: GenderContext.female);

Auto detection is on by default. You can disable auto detection. This may speed up build time.

# File: build.yaml
targets:
  $default:
    builders:
      fast_i18n:
        options:
          contexts:
            gender_context:
              enum:
                - male
                - female
              auto: false # disable auto detection
              paths: # now you must specify paths manually
                - my.path.to.greet

In contrast to pluralization, you must provide all forms. Collapse it to save space.

// File: strings.i18n.json
{
  "greet": {
    "male,female": "Hello $name",
  }
}

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.

// File: strings.i18n.json
{
  "a": {
    "hello world": "hello"
  },
  "b": {
    "b0": "hey",
    "b1": {
      "hi there": "hi"
    }
  }
}

# File: build.yaml
targets:
  $default:
    builders:
      fast_i18n:
        options:
          maps:
            - a
            - b.b1

Now you can access the translations via keys:

String a = t.a['hello world']; // "hello"
String b = t.b.b0; // "hey"
String c = t.b.b1['hi there']; // "hi"

Dynamic Keys #

A more general solution to Maps.

It is supported out of the box. No configuration needed. Please use this sparingly.

String a = t['myPath.anotherPath'];
String b = t['myPath.anotherPath.3']; // with index for arrays
String c = t['myPath.anotherPath'](name: 'Tom'); // with arguments

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"

Fallback #

By default, you must provide all translations for all locales. Otherwise, you cannot compile it.

In case of rapid development, you can turn off this feature. Missing translations will fallback to base locale.

targets:
  $default:
    builders:
      fast_i18n:
        options:
          base_locale: en
          fallback_strategy: base_locale  # add this

// English
{
  "hello": "Hello",
  "bye": "Bye"
}

// French
{
  "hello": "Salut",
  // "bye" is missing, fallback to English version
}

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

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:
        options:
          input_directory: assets/i18n
          output_directory: lib/i18n

Can I skip translations or use them from base locale?

Yes. Please set fallback_strategy: base_locale in build.yaml.

Now you can leave out translations in secondary languages. Missing translations will fallback to base locale.

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.

My plural resolver is not specified?

An exception is thrown by _missingPluralResolver because you missed to add LocaleSettings.setPluralResolver for the specific language.

See Pluralization.

How does auto detection work?

You can let the library detect plurals or contexts.

For plurals, it checks if any json node has zero, one, two, few, many or other as children.

As soon as an unknown item has been detected, then this json node is not a pluralization.

{
  "fake": {
    "one": "One apple",
    "two": "Two apples",
    "three": "Three apples" // unknown key word 'three', 'fake' is not a pluralization
  }
}

For contexts, all enum values must exist.

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.