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fast_i18n #

Lightweight i18n solution. Use JSON, YAML or CSV files to create typesafe translations.

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); // 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
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

PageData page0 = t.onboarding.pages[0];                // with interfaces
PageData page1 = t.onboarding.pages[1];
String h = page1.title; // type-safe call

Getting Started #

Step 1: Add dependencies

It is recommended to add fast_i18n to dev_dependencies.

dev_dependencies:
  build_runner: any
  fast_i18n: 5.10.0

Step 2: Create JSON files

Create these files inside your lib directory. For example, lib/i18n.

YAML and CSV files are also supported (see File Types).

Writing translations into assets folder requires extra configuration (see FAQ).

Format:

<namespace>_<locale?>.<extension>

You can ignore the namespace for this basic example, so just use a generic name like strings or translations.

Example:

lib/
 └── i18n/
      └── strings.i18n.json
      └── strings_de.i18n.json
      └── strings_zh-CN.i18n.json <-- example for country code

// File: strings.i18n.json (mandatory, base locale)
{
  "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);
}

c) use dependency injection (aka "I handle it myself")

final english = AppLocale.en.build();
final german = AppLocale.de.build();

// read
String a = german.login.success;

You can ignore step 4a and 5 (but not 4b) if you handle the locale yourself.

Step 4a: Flutter locale

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

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(TranslationProvider(child: MyApp())); // Wrap your app with TranslationProvider
}

MaterialApp(
  locale: TranslationProvider.of(context).flutterLocale, // use provider
  supportedLocales: LocaleSettings.supportedLocales,
  localizationsDelegates: GlobalMaterialLocalizations.delegates,
  child: YourFirstScreen(),
)

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 # deprecated, use output_file_name
          output_file_name: translations.g.dart
          output_format: single_file
          locale_handling: true
          namespaces: false
          translate_var: t
          enum_name: AppLocale
          translation_class_visibility: private
          key_case: snake
          key_map_case: camel
          param_case: pascal
          string_interpolation: double_braces
          flat_map: false
          timestamp: true
          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
          interfaces:
            PageData: onboarding.pages.*
            PageData2:
              paths:
                - my.path
                - cool.pages.*
              attributes:
                - String title
                - String? content

Key	Type	Usage	Default
`base_locale`	`String`	locale of default json	`en`
`fallback_strategy`	`none`, `base_locale`	handle missing translations (i)	`none`
`input_directory`	`String`	path to input directory	`null`
`input_file_pattern`	`String`	input file pattern, must end with .json, .yaml or .csv	`.i18n.json`
`output_directory`	`String`	path to output directory	`null`
`output_file_pattern`	`String`	deprecated: output file pattern	`.g.dart`
`output_file_name`	`String`	output file name	`null`
`output_format`	`single_file`, `multiple_files`	split output files (i)	`single_file`
`locale_handling`	`Boolean`	generate locale handling logic (i)	`true`
`namespaces`	`Boolean`	split input files (i)	`false`
`translate_var`	`String`	translate variable name	`t`
`enum_name`	`String`	enum name	`AppLocale`
`translation_class_visibility`	`private`, `public`	class visibility	`private`
`key_case`	`null`, `camel`, `pascal`, `snake`	transform keys (optional) (i)	`null`
`key_map_case`	`null`, `camel`, `pascal`, `snake`	transform keys for maps (optional) (i)	`null`
`param_case`	`null`, `camel`, `pascal`, `snake`	transform parameters (optional) (i)	`null`
`string_interpolation`	`dart`, `braces`, `double_braces`	string interpolation mode (i)	`dart`
`flat_map`	`Boolean`	generate flat map (i)	`true`
`timestamp`	`Boolean`	write "Built on" timestamp	`true`
`maps`	`List<String>`	entries which should be accessed via keys (i)	`[]`
`pluralization`/`auto`	`off`, `cardinal`, `ordinal`	detect plurals automatically (i)	`cardinal`
`pluralization`/`cardinal`	`List<String>`	entries which have cardinals	`[]`
`pluralization`/`ordinal`	`List<String>`	entries which have ordinals	`[]`
`<context>`/`enum`	`List<String>`	context forms (i)	no default
`<context>`/`auto`	`Boolean`	auto detect context	`true`
`<context>`/`paths`	`List<String>`	entries using this context	`[]`
`children of interfaces`	`Pairs of Alias:Path`	alias interfaces (i)	`null`

Features #

➤ File Types #

Type	Supported	Note
JSON	✔	by default
YAML	✔	update `input_file_pattern`
CSV	✔	update `input_file_pattern`

To change to YAML or CSV, please modify input_file_pattern.

# File: build.yaml
targets:
  $default:
    builders:
      fast_i18n:
        options:
          input_directory: assets/i18n
          input_file_pattern: .i18n.yaml # must end with .json, .yaml or .csv

JSON Example

{
  "welcome": {
    "title": "Welcome $name"
  }
}

YAML Example

welcome:
  title: Welcome $name # some comment

CSV Example

You may also combine multiple locales into one CSV (see Compact CSV).

key,translation

welcome.title,Welcome $name
welcome.pages.0.title,First Page
welcome.pages.1.title,Second Page

➤ Namespaces #

You can split the translations into multiple files. Each file represents a namespace.

This feature is disabled by default for single-file usage. You must enable it.

# File: build.yaml
targets:
  $default:
    builders:
      fast_i18n:
        options:
          namespaces: true # enable this feature
          output_directory: lib/i18n # optional
          output_file_name: translations.g.dart # set file name (mandatory)

Let's create two namespaces called widgets and dialogs.

<namespace>_<locale?>.<extension>

i18n/
 └── widgets.i18n.json
 └── widgets_fr.i18n.json
 └── dialogs.i18n.json
 └── dialogs_fr.i18n.json

You can also use different folders. Only file name matters!

i18n/
 └── widgets/
      └── widgets.i18n.json
      └── widgets_fr.i18n.json
 └── dialogs/
      └── dialogs.i18n.json
      └── dialogs_fr.i18n.json

i18n/
 └── en/
      └── widgets.i18n.json
      └── dialogs.i18n.json
 └── fr/
      └── widgets_fr.i18n.json
      └── dialogs_fr.i18n.json

Now access the translations:

// t.<namespace>.<path>
String a = t.widgets.welcomeCard.title;
String b = t.dialogs.logout.title;

➤ 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}.

Mode	Example
`dart (default)`	`Hello $name. I am ${height}m.`
`braces`	`Hello {name}`
`double_braces`	`Hello {{name}}`

➤ 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"

➤ Linked Translations #

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

{
  "fields": {
    "name": "my name is {firstName}",
    "age": "I am {age} years old"
  },
  "introduce": "Hello, @:fields.name and @:fields.age"
}

String s = t.introduce(firstName: 'Tom', age: 27); // Hello, my name is Tom and I am 27 years old.

➤ Interfaces #

Often, multiple objects have the same attributes. You can create a common super class for that.

{
  "onboarding": {
    "whatsNew": {
      "v2": {
        "title": "New in 2.0",
        "rows": [
          "Add sync"
        ]
      },
      "v3": {
        "title": "New in 3.0",
        "rows": [
          "New game modes",
          "And a lot more!"
        ]
      }
    }
  }
}

Here we know that all objects inside whatsNew have the same attributes. Let's name these objects ChangeData.

# File: build.yaml
targets:
  $default:
    builders:
      fast_i18n:
        options:
          interfaces:
            ChangeData: onboarding.whatsNew.*

void myFunction(ChangeData changes) {
  String title = changes.title;
  List<String> rows = changes.rows;
}

void main() {
  myFunction(t.onboarding.whatsNew.v2);
  myFunction(t.onboarding.whatsNew.v3);
}

You can customize the attributes and use different node selectors.

Checkout the full article.

➤ 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,
}

// extension methods
Locale locale = AppLocale.en.flutterLocale; // to native flutter locale
String tag = AppLocale.en.languageTag; // to string tag (e.g. en-US)
final t = AppLocale.en.translations; // get translations of one locale

➤ Dependency Injection #

You don't like the included LocaleSettings solution?

Then you can use your own dependency injection solution!

Just create custom translation instances that don't depend on LocaleSettings or any other side effects.

First, set the following configuration:

# File: build.yaml
targets:
  $default:
    builders:
      fast_i18n:
        options:
          locale_handling: false # remove unused t variable, LocaleSettings, etc.
          translation_class_visibility: public

Example using the riverpod library:

final english = AppLocale.en.build(cardinalResolver: myEnResolver);
final german = AppLocale.de.build(cardinalResolver: myDeResolver);
final translationProvider = StateProvider<StringsEn>((ref) => german); // set it

// access the current instance
final t = ref.watch(translationProvider);
String a = t.welcome.title;

Checkout the full article.

➤ 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.

// 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.

The detected plurals are cardinals by default.

In general, you will probably use only this variant. Ordinals are rarely used. If your project only has cardinals, then you don't need to configure anything! It works out of the box.

However, if you have ordinals, then you will need some configurations.

// File: strings.i18n.json
{
  "someKey": {
    "apple": {
      // cardinal
      "one": "I have $count apple.",
      "other": "I have $count apples."
    },
    "place": {
      // ordinal (rarely used)
      "one": "${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!;
  },
);

By default, the parameter name is count. You can change that by adding a hint.

{
  "someKey": {
    "apple(appleCount)": {
      "one": "I have one apple.",
      "other": "I have multiple apples."
    }
  }
}

String a = t.someKey.apple(appleCount: 2); // notice 'appleCount' instead of 'count'

➤ 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.

{
  "greet": {
    "male,female": "Hello $name"
  }
}

Similarly to plurals, the parameter name is context by default. You can change that by adding a hint.

{
  "greet(gender)": {
    "male": "Hello Mr",
    "female": "Hello Ms"
  }
}

String a = t.greet(gender: GenderContext.female); // notice 'gender' instead of 'context'

➤ Maps #

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

Define maps in your build.yaml.

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 / Flat Map #

A more general solution to Maps. ALL translations are accessible via an one-dimensional map.

It is supported out of the box. No configuration needed.

This can be disabled globally by setting flat_map: false.

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

➤ 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
}

➤ Recasing #

By default, no transformations will be applied.

You can change that by specifying key_case, key_map_case or param_case.

Possible cases are: camel, snake and pascal.

{
  "must_be_camel_case": "The parameter is in {snakeCase}",
  "my_map": {
    "this_should_be_in_pascal": "hi"
  }
}

targets:
  $default:
    builders:
      fast_i18n:
        options:
          key_case: camel
          key_map_case: pascal
          param_case: snake
          maps:
            - myMap # all paths must be cased accordingly

String a = t.mustBeCamelCase(snake_case: 'nice');
String b = t.myMap['ThisShouldBeInPascal'];

➤ Output Format #

By default, a single .g.dart file will be generated.

You can split this file into multiple ones to improve readability and IDE performance.

targets:
  $default:
    builders:
      fast_i18n:
        options:
          output_file_name: translations.g.dart
          output_format: multiple_files # set this

This will generate the following files:

lib/
 └── i18n/
      └── translations.g.dart <-- main file
      └── translations_en.g.dart <-- translation classes
      └── translations_de.g.dart <-- translation classes
      └── ...
      └── translations_map.g.dart <-- translations stored in flat maps

You only need to import the main file!

➤ Compact CSV #

Normally, you would create a new csv file for each locale: strings.i18n.csv, strings_fr.i18n.csv, etc.

You can also merge multiple locales into one single csv file! To do this, you need at least 3 columns. The first row contains the locale names. This library should detect that, so no configuration is needed.

   ,locale_0,locale_1, ... ,locale_n
key,string_0,string_1, ... ,string_n

key,en,de-DE
welcome.title,Welcome $name,Willkommen $name

assets/
 └── i18n/
      └── strings.i18n.csv <-- contains all locales

➤ 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

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.

Can I prevent the timestamp Built on from updating?

No, but you can disable the timestamp altogether. Set timestamp: false in build.yaml.

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 your 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 plural / context 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.

How can I use multiple plurals in one sentence?

You may use linked translations to solve this problem.

{
  "apples(appleCount)": {
    "one": "one apple",
    "other": "{appleCount} apples"
  },
  "bananas(bananaCount)": {
    "one": "one banana",
    "other": "{bananaCount} bananas"
  },
  "sentence": "I have @:apples and @:bananas"
}

String a = t.sentence(appleCount: 1, bananaCount: 2); // two different plural parameters!

What's the difference between AppLocale.en.translations and AppLocale.en.build()?

The plural resolvers of AppLocale.<locale>.translations must be set via LocaleSettings.setPluralResolver. Therefore, calls on LocaleSettings has side effects on AppLocale.<locale>.translations.

When you call AppLocale.<locale>.build(), there are no side effects.

Furthermore, the first method returns the instance managed by this library. The second one always returns a new instance.

License #

MIT License

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.

fast_i18n 5.10.0
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Metadata

fast_i18n #

About this library #

Table of Contents #

Getting Started #

Configuration #

Features #

➤ File Types #

➤ Namespaces #

➤ String Interpolation #

➤ Lists #

➤ Linked Translations #

➤ Interfaces #

➤ Locale Enum #

➤ Dependency Injection #

➤ Pluralization #

➤ Custom Contexts #

➤ Maps #

➤ Dynamic Keys / Flat Map #

➤ Fallback #

➤ Recasing #

➤ Output Format #

➤ Compact CSV #

➤ Auto Rebuild #

FAQ #

Further Reading #

License #

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fast_i18n 5.10.0 fast_i18n: ^5.10.0 copied to clipboard

Metadata

fast_i18n #

About this library #

Table of Contents #

Getting Started #

Configuration #

Features #

➤ File Types #

➤ Namespaces #

➤ String Interpolation #

➤ Lists #

➤ Linked Translations #

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Further Reading #

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fast_i18n 5.10.0
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