Tienisto/slang

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

An extensive CLI will help you to manage the translations:

dart run slang                               # generate dart file
dart run slang analyze                       # unused and missing translations
dart run slang edit move loginPage authPage  # move or rename translations
dart run slang migrate arb src.arb dest.json # migrate arb to json

Table of Contents

• Getting Started
• Configuration
• Main Features
  • File Types
  • String Interpolation
  • RichText
  • Lists
  • Maps
  • Dynamic Keys
  • Changing Locale
• Complex Features
  • Linked Translations
  • Pluralization
  • Custom Contexts / Enums
  • Interfaces
  • Modifiers
  • Locale Enum
  • Locale Stream
  • Translation Overrides
  • Dependency Injection
• Structuring Features
  • Namespaces
  • Output Format
  • Compact CSV
• Other Features
  • Fallback
  • Comments
  • Recasing
  • Obfuscation
  • Dart Only
• Tools
  • Main Command
  • Analyze Translations
  • Apply Translations
  • Edit Translations
  • Outdated Translations
  • Migration
    • ARB
  • Statistics
  • Auto Rebuild
• More Usages
  • Assets
  • Unit Tests
• Integrations
  • slang x riverpod
• FAQ
• Further Reading
• Apps built with slang

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

Step 2: Create JSON files

Format:

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

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

Most common i18n directories are assets/i18n and lib/i18n. (see Assets).

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:

# Recommended during development. It runs much faster than build_runner.

dart run slang

Alternative (requires slang_build_runner):

# Useful for CI and initial git checkout.

dart run build_runner build -d

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: AppLocaleUtils.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.

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
obfuscation:
  enabled: false
  secret: somekey
imports:
  - 'package:my_package/path_to_enum.dart'

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
          obfuscation:
            enabled: false
            secret: somekey
          imports:
            - 'package:my_package/path_to_enum.dart'

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

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

➤ Changing Locale

If you use the built-in LocaleSettings solution, then it is quite easy to change the locale.

The TranslationProvider listens to locale changes from the device.

• LocaleSettings.useDeviceLocale will enable the listener.
• LocaleSettings.setLocale and LocaleSettings.setLocaleRaw will disable the listener by default.

Widgets rebuild only if you use final t = Translations.of(context) or context.t.

Complex Features

➤ Linked Translations

You can link one translation to another. Add the prefix @: followed by the absolute path of the desired translation.

{
  "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.

If namespaces are used, then it has to be specified in the path too.

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(
  locale: AppLocale.en,
  cardinalResolver: (n, {zero, one, two, few, many, other}) {
    if (n == 0)
      return zero ?? other!;
    if (n == 1)
      return one ?? other!;
    return other!;
  },
  ordinalResolver: (n, {zero, one, two, few, many, 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(context=GenderContext)": {
    "male": "Hello Mr $name",
    "female": "Hello Ms $name"
  }
}

The following enum will be generated for you:

enum GenderContext {
  male,
  female,
}

So you can use it like this:

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

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

{
  "greet(context=GenderContext)": {
    "male,female": "Hello $name"
  }
}

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

{
  "greet(context=GenderContext, 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:
  GenderContext:
    default_parameter: gender # 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:
    generate_enum: false # turn off enum generation

➤ Interfaces

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

Add the (interface=<Interface Name>) to the container node.

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

Alternatively, you can specify them in the global config:

# Config
interfaces:
  ChangeData: onboarding.whatsNew.*

The following mixin will be generated automatically 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) {
  List<String> rows = changes.rows as List<String>; // Not type-safe! Prone to typos!
}

// after: using interfaces
void myFunction(ChangeData changes) {
  List<String> rows = changes.rows; // Type-safe! No need to worry!
}

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.

➤ Modifiers

There are several 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:

Analysis Modifiers (only used for the analysis tool):

➤ 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

➤ Locale Stream

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

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

➤ 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; // get translation
AppLocale locale = t.$meta.locale; // get locale

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 errorDialogs. Please use camel case for multiple words.

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

i18n/
 └── widgets.i18n.json
 └── widgets_fr.i18n.json
 └── errorDialogs.i18n.json <-- camel case for multiple words
 └── errorDialogs_fr.i18n.json

You can also use different folders. The namespace is only dependent on the file name!

i18n/
 └── widgets/
      └── widgets.i18n.json
      └── widgets_fr.i18n.json
 └── errorDialogs/
      └── errorDialogs.i18n.json
      └── errorDialogs_fr.i18n.json

i18n/
 └── en/
      └── widgets.i18n.json
      └── error_dialogs.i18n.json
 └── fr/
      └── widgets-fr.i18n.json
      └── error_dialogs.i18n.json <-- directory locale will be used

If you use directory locales, then you may use underscores as namespace.

Now access the translations:

// t.<namespace>.<path>
String a = t.widgets.welcomeCard.title;
String b = t.errorDialogs.login.wrongPassword;

➤ 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(map)": {
    "this_should_be_in_pascal": "hi"
  }
}

# Config
key_case: camel
key_map_case: pascal
param_case: snake

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

If you specify paths in the config, please case them correctly:

# Config
key_case: camel
maps:
   - myMap # all paths must be cased accordingly

➤ Obfuscation

Obfuscate the translation strings to make reverse engineering harder.

You should also enable Flutter obfuscation for additional security.

# Config
obfuscation:
  enabled: true
  secret: somekey # set this if you want deterministic obfuscation

That's all. Everything should work like before.

Now, instead of this:

String get hello => 'Hello';

The following will be generated:

String get hello => _root.$meta.d([104, 69, 76, 76, 79]);

The secret key itself is hidden in the generated code.

XOR is used for encryption to keep your app (nearly) as fast as before.

Keep in mind that this only prevents simple string searches of the binary.

An experienced reverse engineer can still find the strings given enough time.

➤ 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.

dart run slang

➤ Analyze Translations

You can use the slang analyzer to find missing and unused translations.

Missing translations only occur when fallback_strategy: base_locale is used.

dart run slang analyze [--split] [--full] [--outdir=assets/i18n]

Result file:

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

You can ignore a specific node by adding an (ignoreMissing) or (ignoreUnused) modifier.

➤ Apply Translations

The follow-up command for analyze.

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

Currently, only JSON and YAML are supported.

dart run slang apply [--locale=fr-FR] [--outdir=assets/i18n]

➤ Edit Translations

You can use this command to rename, remove, or add translation keys. This is useful when you have many locales, or if you just want to use the command line.

dart run slang edit <type> <params...>

* See Outdated Translations

➤ Outdated Translations

You want to update an existing string, but you want to keep the old translations for other locales?

Here, you can run a simple command to flag translations as OUTDATED. They will show up in _missing_translations when running analyze.

dart run slang edit outdated a.b.c

# shorthand
dart run slang outdated a.b.c

This will add an (OUTDATED) modifier to all secondary locales.

{
  "a": {
    "b": {
      "c(OUTDATED)": "This translation is outdated"
    }
  }
}

You can also add these flags manually!

➤ Migration

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

General migration syntax:

dart run slang migrate <type> <source> <destination>

ARB

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

dart 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(param=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.

dart 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.

dart run slang watch

More Usages

➤ Assets

You can write the i18n files wherever you want.

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 # defaulting to lib/gen if input is outside of lib/

... or in slang.yaml:

input_directory: assets/i18n
output_directory: lib/i18n # defaulting to lib/gen if input is outside of lib/

➤ Unit Tests

It is recommended to add at least one test that accesses the translations to make sure that they are compiled correctly.

Because slang is type-safe, this test is most likely enough to ensure that the translations are working.

import 'package:my_app/gen/strings.g.dart';
import 'package:test/test.dart';

void main() {
  group('i18n', () {
    test('should compile', () {
      // The following test will fail if the i18n file is either not compiled
      // or there are compile-time errors.
      expect(AppLocale.en.build().aboutPage.title, 'About');
    });
  });
}

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

Translations don't update when device locale changes

By default, this library does not listen to locale changes from device.

To enable this, either use LocaleSettings.useDeviceLocale or set listenToDeviceLocale: true when changing the locale.

Additionally, wrap your app with TranslationProvider and get the translations via final t = Translations.of(context).

CSV files are not parsed correctly

Note that translated EOL should be written as \n.

CORRECT:

my.path,hello\nworld

WRONG:

my.path,hello<LF>
world

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(param=appleCount)": {
    "one": "one apple",
    "other": "{appleCount} apples"
  },
  "bananas(param=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

Blogs

• Medium (English)
• Хабр (Russian)
• Qiita (Japanese)
• okaryo (Japanese)
• zenn (Japanese)
• zenn (Japanese)

Videos

• Youtube (Korean)
• Youtube (Spanish)
• Zhihu (Chinese)

Feel free to extend this list :)

Apps built with slang

Open source:

• LocalSend (file sharing app)
• Saber (notes app)
• Boorusphere (booru viewer)
• Flutter Advanced Boilerplate (boilerplate project)

Closed source:

• Notan (grade calculator)

Feel free to extend this list :)

License

MIT License

Copyright (c) 2020-2023 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.