slang 3.3.0

Localization / Internationalization (i18n) solution. Use JSON, YAML or CSV files to create typesafe translations via source generation.

slang

[s]tructured [lan]guage file [g]enerator

Type-safe i18n solution using JSON, YAML or CSV files.

The official successor of fast_i18n.

About this library

• 🚀 Minimal setup, create JSON files and get started! No configuration needed.
• 🐞 Bug-resistant, no typos or missing arguments possible due to compile-time checking.
• ⚡ Fast, you get translations using native dart method calls, zero parsing!
• 📁 Organized, split large files into smaller ones via namespaces.
• 🔨 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(n: 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
TextSpan h = t.greet(name: TextSpan(text: 'Tom'));     // with RichText

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

Table of Contents

• Getting Started
• Configuration
• Main Features
  • File Types
  • String Interpolation
  • RichText
  • Lists
  • Maps
  • Dynamic Keys
  • Modifiers
• Complex Features
  • Linked Translations
  • Pluralization
  • Custom Contexts / Enums
  • Locale Stream
  • Interfaces
  • Locale Enum
  • Translation Overrides
  • Dependency Injection
• Structuring Features
  • Namespaces
  • Output Format
  • Compact CSV
• Other Features
  • Fallback
  • Comments
  • Recasing
  • Dart Only
• Tools
  • Main Command
  • Missing and Unused Translations
  • Apply Translations
  • Migration
    • ARB
  • Statistics
  • Auto Rebuild
• Integrations
  • slang X riverpod
• FAQ
• Further Reading

Getting Started

Coming from ARB? There is a tool for that.

Step 1: Add dependencies

You will probably need at least 2 packages: slang and slang_flutter.

dependencies:
  slang: <version>
  slang_flutter: <version> # also add this if you use flutter

dev_dependencies:
  build_runner: <version> # if you use build_runner (1/2)
  slang_build_runner: <version> # if you use build_runner (2/2)

Step 2: Create JSON files

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

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.

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

Built-in:

flutter pub run slang

Alternative (requires slang_build_runner):

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 a slang.yaml or a build.yaml file. Place it in the root directory.

slang.yaml (Click to open example)

If you don't use build_runner, then you can define your config in slang.yaml for less boilerplate.

base_locale: fr
fallback_strategy: base_locale
input_directory: lib/i18n
input_file_pattern: .i18n.json
output_directory: lib/i18n
output_file_name: translations.g.dart
output_format: single_file
locale_handling: true
flutter_integration: 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
translation_overrides: false
timestamp: true
maps:
  - error.codes
  - category
  - iconNames
pluralization:
  auto: cardinal
  default_parameter: n
  cardinal:
    - someKey.apple
  ordinal:
    - someKey.place
contexts:
  gender_context:
    enum:
      - male
      - female
    paths:
      - my.path.to.greet
    default_parameter: gender
    generate_enum: true
interfaces:
  PageData: onboarding.pages.*
  PageData2:
    paths:
      - my.path
      - cool.pages.*
    attributes:
      - String title
      - String? content
imports:
  - 'package:my_package/path_to_enum.dart'

build.yaml (Click to open example)

Using build.yaml is necessary if you use build_runner.

targets:
  $default:
    builders:
      slang_build_runner:
        options:
          base_locale: fr
          fallback_strategy: base_locale
          input_directory: lib/i18n
          input_file_pattern: .i18n.json
          output_directory: lib/i18n
          output_file_name: translations.g.dart
          output_format: single_file
          locale_handling: true
          flutter_integration: 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
          translation_overrides: false
          timestamp: true
          maps:
            - error.codes
            - category
            - iconNames
          pluralization:
            auto: cardinal
            default_parameter: n
            cardinal:
              - someKey.apple
            ordinal:
              - someKey.place
          contexts:
            gender_context:
              enum:
                - male
                - female
              paths:
                - my.path.to.greet
              default_parameter: gender
              generate_enum: true
          interfaces:
            PageData: onboarding.pages.*
            PageData2:
              paths:
                - my.path
                - cool.pages.*
              attributes:
                - String title
                - String? content
          imports:
            - 'package:my_package/path_to_enum.dart'

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_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
flutter_integration	Boolean	generate flutter features (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
translation_overrides	Boolean	enable translation overrides (i)	false
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/default_parameter	String	default plural parameter (i)	n
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>/paths	List<String>	entries using this context	[]
<context>/default_parameter	String	default parameter name	context
<context>/generate_enum	Boolean	generate enum	true
children of interfaces	Pairs of Alias:Path	alias interfaces (i)	null
imports	List<String>	generate import statements	[]

Main Features

➤ File Types

Supported file types: JSON (default), YAML and CSV.

To change to YAML or CSV, please modify input_file_pattern.

# Config
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

Line terminations must be CRLF.

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

# Format: <key>, <translation>

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

➤ String Interpolation

Translations often have a dynamic parameter. There are multiple ways to define them.

# Config
string_interpolation: dart # change to braces or double_braces

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

dart (default)

Hello $name. I am ${height}m.

braces

Hello {name}

double_braces

Hello {{name}}

➤ RichText

You can add multiple styles to one translation.

To do this, please add the (rich) modifier.

Parameters are formatted according to string_interpolation.

Default text can be defined via brackets (...), e.g. underline(here).

{
  "myText(rich)": "Welcome $name. Please click ${tapHere(here)}!"
}

Usage:

// Text.rich is a Flutter built-in feature!
Widget a = Text.rich(t.myText(
  // Show name in blue color
  name: TextSpan(text: 'Tom', style: TextStyle(color: Colors.blue)),
  
  // Turn 'here' into a link
  tapHere: (text) => TextSpan(
    text: text,
    style: TextStyle(color: Colors.blue),
    recognizer: TapGestureRecognizer()..onTap=(){
      print('tap');
    },
  ),
));

➤ 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"

➤ Maps

You can access each translation via string keys.

Add the (map) modifier.

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

For large projects with lots of locales, it may be better to specify them in the config file.

# Config
maps: # Applies to all locales!
  - 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

➤ Modifiers

There are multiple modifiers for further adjustments.

You can combine multiple modifiers with commas like this:

{
  "apple(plural, param=appleCount, rich)": {
    "one": "I have $appleCount apple.",
    "other": "I have $appleCount apples."
  }
}

Available Modifiers:

Modifier	Meaning	Applicable for
(rich)	This is a rich text.	Leaves, Maps (Plural / Context)
(map)	This is a map / dictionary (and not a class).	Maps
(plural)	This is a plural (type: cardinal)	Maps
(cardinal)	This is a plural (type: cardinal)	Maps
(ordinal)	This is a plural (type: ordinal)	Maps
(context=<Context Type>)	This is a context of type <Context Type>	Maps
(param=<Param Name>)	This has the parameter <Param Name>	Maps (Plural / Context)

Complex Features

➤ 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.

RichTexts can also contain links! But only RichTexts can link to RichTexts.

➤ 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 $n apple.",
      "other": "I have $n apples."
    }
  }
}

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

The detected plurals are cardinals by default.

To specify ordinals, you need to add the (ordinal) modifier.

// File: strings.i18n.json
{
  "someKey": {
    "apple(cardinal)": {
      // cardinal
      "one": "I have $n apple.",
      "other": "I have $n apples."
    },
    "place(ordinal)": {
      // ordinal (rarely used)
      "one": "${n}st place.",
      "two": "${n}nd place.",
      "few": "${n}rd place.",
      "other": "${n}th place."
    }
  }
}

You can also specify all plural forms in the global config.

# Config
pluralization: # Applies to all locales!
  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 n. You can change that by adding a modifier.

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

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

You can set the default parameter globally via pluralization/default_parameter.

➤ Custom Contexts / Enums

You can utilize custom contexts to differentiate between male and female forms (or other enums).

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

# Config
contexts:
  GenderContext:
    enum:
      - male
      - female
  UserType:
    enum:
      - user
      - admin

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.

# Config
contexts:
  GenderContext:
    enum:
      - male
      - female
    paths: # only these paths will be considered
      - 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 modifier.

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

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

... or set it globally:

# Config
contexts:
  UserType:
    enum:
      - user
      - admin
    default_parameter: type # by default: "context"

You already have an existing enum? Import it instead!

# Config
imports:
  - 'package:my_package/path_to_enum.dart' # define where your enum is
contexts:
  UserType:
    enum:
      - user
      - admin
    generate_enum: false # turn off enum generation

➤ Locale Stream

You may want to track locale changes. Please use LocaleSettings.getLocaleStream.

LocaleSettings.getLocaleStream().listen((event) {
  print('locale changed: $event');
});

➤ 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.

# Config
interfaces:
  ChangeData: onboarding.whatsNew.*

The following mixin will be automatically generated for you:

mixin ChangeData {
  String get title;
  List<String> get rows;
}

Now you can access these fields using polymorphism:

// before: without interfaces
void myOldFunction(dynamic changes) {
  String title = changes.title; // not type safe!
  List<String> rows = changes.rows; // prone to typos
}

// after: using interfaces
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

➤ Translation Overrides

You may want to update translations dynamically (e.g. via backend server over network).

Set the following configuration:

# Config
translation_overrides: true

Example:

// override
LocaleSettings.overrideTranslations(
  locale: AppLocale.en,
  fileType: FileType.yaml,
  content: r'''
onboarding
  title: 'Welcome {name}'
  '''
);

// access
String a = t.onboarding.title(name: 'Tom'); // "Welcome Tom"

A few remarks:

1. New translations will be parsed but have no effect.
2. New parameters stay unparsed. (i.e. {name} stays {name})
3. Missing translations will use translations before the override.
4. Overriding a second time reverts the last override.

➤ 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:

# Config
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.

Structuring Features

➤ 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.

# Config
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.i18n.json <-- directory locale will be used

Now access the translations:

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

➤ 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.

# Config
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.

Comments are supported. (see Comments)

     ,locale_0 ,locale_1 , ... ,locale_n
key_0,string_00,string_01, ... ,string_0n
key_1,string_10,string_11, ... ,string_1n
...
key_m,string_m0,string_m1, ... ,string_mn

Example:

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

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

Other Features

➤ 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.

# Config
base_locale: en
fallback_strategy: base_locale # add this

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

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

➤ Comments

You can add comments in your translation files.

JSON

All keys starting with @ will be ignored.

If a @key key matches an existing key, then its value will be rendered as a comment.

{
  "@@locale": "en", // fully ignored
  "mainScreen": {
    "button": "Submit",

    // ignored as translation but rendered as a comment
    "@button": "The submit button shown at the bottom",

    // ARB style is also possible, the description will be rendered as a comment
    "@button2": {
      "context": "HomePage",
      "description": "The submit button shown at the bottom"
    },
  }
}

YAML

Currently, not parsed and no comments will be generated.

mainScreen:
  button: Submit # The submit button shown at the bottom

CSV

Columns with parentheses like (my_column) are ignored.

Values in the first column with parentheses will be rendered as a comment.

key,(comment),en,de,(ignored comment)
mainScreen.button,The submit button shown at the bottom,Submit,Bestätigen,fully ignored
mainScreen.content,,Content,Inhalt,

Generated File

/// The submit button shown at the bottom
String get button => 'Submit';

➤ 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"
  }
}

# Config
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'];

➤ Dart Only

You can use this library without flutter.

# Config
flutter_integration: false # set this

Tools

➤ Main Command

The main command to generate dart files from translation resources.

flutter pub run slang

➤ Missing and Unused Translations

You can find missing and unused translations by running a single command.

Missing translations only occurs when fallback_strategy: base_locale is used.

flutter pub run slang analyze [--split] [--flat] [--full] [--outdir=assets/i18n]

Argument	Usage
--split	Generate for each locale
--flat	Generate parent as path to reduce nesting
--full	Find unused translations in whole source code
--outdir=<dir>	Path of analysis output (input_directory by default)

Result file:

{
  "de": {
    "mainScreen": {
      "login": "This translation is missing, showing base translation here"
    }
  },
  "fr": {} // everything ok
}

➤ Apply Translations

The follow-up command for flutter pub run slang analyze.

It reads the _missing_translations file and adds the translations to the original files.

Currently, only JSON and YAML are supported.

flutter pub run slang apply [--flat] [--outdir=assets/i18n]

Argument	Usage
--flat	Missing translations file is in flat format
--outdir=<dir>	Path of analysis output (input_directory by default)

➤ Migration

There are some tools to make migration from other i18n solutions easier.

General migration syntax:

flutter pub run slang migrate <type> <source> <destination>

ARB

Transforms ARB files to compatible JSON format. All descriptions are retained.

flutter pub run slang migrate arb source.arb destination.json

ARB Input

{
  "@@locale": "en_US",
  "@@context": "HomePage",
  "title_bar": "My Cool Home",
  "@title_bar": {
    "type": "text",
    "context": "HomePage",
    "description": "Page title."
  },
  "FOO_123": "Your pending cost is {COST}",
  "foo456": "Hello {0}",
  "pageHomeInboxCount" : "{count, plural, zero{You have no new messages} one{You have 1 new message} other{You have {count} new messages}}",
  "@pageHomeInboxCount" : {
    "placeholders": {
      "count": {}
    }
  }
}

JSON Result

{
  "@@locale": "en_US",
  "@@context": "HomePage",
  "title": {
    "bar": "My Cool Home",
    "@bar": "Page title."
  },
  "foo123": "Your pending cost is {cost}",
  "foo456": "Hello {arg0}",
  "page": {
    "home": {
      "inbox": {
        "count(count)": {
          "zero": "You have no new messages",
          "one": "You have 1 new message",
          "other": "You have {count} new messages"
        }
      }
    }
  }
}

➤ Statistics

There is a command to quickly get the number of words, characters, etc.

flutter pub run slang stats

Example console output:

[en]
 - 9 keys (including intermediate keys)
 - 6 translations (leaves only)
 - 15 words
 - 82 characters (ex. [,.?!'¿¡])

➤ Auto Rebuild

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

flutter pub run slang watch

Integrations

➤ slang x riverpod

Method A: Use static getter

Access translation variable t directly, use LocaleSettings.setLocale to change locales.

Track locale changes with LocaleSettings.getLocaleStream():

final localeProvider = StreamProvider((ref) => LocaleSettings.getLocaleStream());

Method B: Use dependency injection

Checkout Dependency Injection.

FAQ

Can I write the json files in the asset folder?

Yes. Specify input_directory and output_directory in build.yaml.

targets:
  $default:
    sources:
      - "custom-directory/**" # optional; only assets/* and lib/* are scanned by build_runner
    builders:
      slang_build_runner:
        options:
          input_directory: assets/i18n
          output_directory: lib/i18n

... or in slang.yaml:

input_directory: assets/i18n
output_directory: lib/i18n

CSV files are not parsed correctly

Note that line terminations must be CRLF.

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.

Further Reading

In Depth

Interfaces

Dependency Injection

Tutorials

Medium (English)

Qiita (Japanese)

Youtube (Korean)

Feel free to extend this list :)

License

MIT License

Copyright (c) 2020-2022 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.