Translate Flutter
ARB Files

Upload your .arb files, translate values while keeping descriptions and plurals intact, and export files the intl package loads without changes.

Translate ARB file
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app_en.arb
{ "@@locale": "en", "home.interface.signup": "Signup", "@home.interface.signup": { "description": "Text on the signup button" } }
{
  "@@locale": "en",
  "home.interface.signup": "Signup",
  "@home.interface.signup": {
    "description": "Text on the signup button"
  }
}

Why teams use ARB for translations

ARB (Application Resource Bundle) is essentially a single-language JSON file with one addition: a required @@locale field naming the file's language, and an optional @key metadata object next to any translation key. Since it's built for the Intl package, ARB doesn't support nested keys or arrays, only flat key-value pairs.

Metadata under @key can hold a description for translators, plus any custom property like context or author, none of which are required by Flutter itself but travel with the key wherever it goes.

Custom metadata
"home.interface.signup": "Signup", "@home.interface.signup": { "description": "Text on the signup button", "context": "Auth screen", "author": "John Doe" }
"home.interface.signup": "Signup",
"@home.interface.signup": {
  "description": "Text on the signup button",
  "context": "Auth screen",
  "author": "John Doe"
}

Beyond key and value

ARB files in SimpleLocalize

Metadata as context

The description field under a key's @ entry imports as translator context automatically.

ICU pluralization

Keys following Flutter's zero/one/two/few/many/other convention are recognized as one pluralized string.

One file per language

Files are typically named messages_en.arb, messages_pl.arb, and so on, one language per file.

Custom properties preserved

Extra @key properties like context or author are kept as key metadata, not just the description.

End-to-end workflow

Translate an ARB file end to end

Upload a source app_en.arb file, translate values while keeping descriptions and plurals intact, and download one file per language.

Terminal
simplelocalize upload \ --apiKey PROJECT_API_KEY \ --uploadFormat arb \ --uploadLanguageKey en \ --uploadPath ./app_en.arb
simplelocalize upload \
  --apiKey PROJECT_API_KEY \
  --uploadFormat arb \
  --uploadLanguageKey en \
  --uploadPath ./app_en.arb

Upload your source ARB file

1
Push app_en.arb to SimpleLocalize with the CLI. The @@locale field and any @key descriptions import automatically.
Translation editor
Key: home.interface.signup Source: Signup Context: Text on the signup button
Key: home.interface.signup
Source: Signup
Context: Text on the signup button

Descriptions land as context

2
A key's @key description shows up next to it in the editor, so a translator sees exactly what a developer meant without asking.
app_pl.arb (auto-translated)
"notifications_zero": "Brak powiadomień", "notifications_one": "Masz jedno powiadomienie", "notifications_other": "Masz {count} powiadomienia"
"notifications_zero": "Brak powiadomień",
"notifications_one": "Masz jedno powiadomienie",
"notifications_other": "Masz {count} powiadomienia"

Auto-translate, plurals included

3
Run DeepL, Google Translate, OpenAI, Claude or Gemini across every target language. notifications_zero, _one and _other keys translate together as one ICU-format string.
Terminal
simplelocalize download \ --apiKey PROJECT_API_KEY \ --downloadFormat arb \ --downloadPath ./app_{lang}.arb
simplelocalize download \
  --apiKey PROJECT_API_KEY \
  --downloadFormat arb \
  --downloadPath ./app_{lang}.arb

Download one file per language

4
Export lands as app_{lang}.arb, ready for the flutter generate command to turn into typed Dart localization classes.

For developers

A localization platform,
not just an ARB parser

SimpleLocalize reads the parts of ARB that go beyond plain JSON, and gives your team a place to manage the translations behind them.

Metadata as context

The description field under a key's @ entry is imported as translator context automatically, along with any custom properties.

ICU pluralization

Keys following Flutter's plural naming convention are recognized and editable as one pluralized string, matching how the Intl package expects them.

AI auto-translation

Translate new and changed keys with DeepL, Google Translate, OpenAI, Claude or Gemini.

CLI and REST API

Upload and download ARB files from the CLI, or automate the same logic through the REST API.

SimpleLocalize connects your code to professional translations

In your Flutter app

Setting up ARB with the Intl package

Configuring i18n in Flutter with ARB is a multistep process: install the intl package, generate Dart code from your ARB files, then load and use the translations.

pubspec.yaml
dependencies: flutter: sdk: flutter flutter_localizations: sdk: flutter intl: ^0.19.0
dependencies:
  flutter:
    sdk: flutter
  flutter_localizations:
    sdk: flutter
  intl: ^0.19.0

Add dependencies

1
Add the intl package to your pubspec.yaml file, and run flutter pub get. See the newest version on pub.dev.
lib/l10n/messages_pl.arb
{ "@@locale": "pl", "greeting": "Witaj, {name}!", "@greeting": { "description": "Greeting message" } }
{
  "@@locale": "pl",
  "greeting": "Witaj, {name}!",
  "@greeting": {
    "description": "Greeting message"
  }
}

Create your ARB files

2
Create one ARB file per language you support, either by hand or exported from SimpleLocalize via the CLI or the translation editor.
pubspec.yaml
flutter: generate: true l10n: arb-dir: lib/l10n template-arb-file: messages_en.arb output-localization-file: app_localizations.dart
flutter:
  generate: true
  l10n:
    arb-dir: lib/l10n
    template-arb-file: messages_en.arb
    output-localization-file: app_localizations.dart

Generate Dart code

3
Configure l10n in pubspec.yaml, then run flutter generate to produce an AppLocalizations class from your ARB files.
main.dart
MaterialApp( localizationsDelegates: [ AppLocalizations.delegate, GlobalMaterialLocalizations.delegate, ], supportedLocales: [Locale('en'), Locale('pl')], ) Text(AppLocalizations.of(context).greeting('Alicja'))
MaterialApp(
  localizationsDelegates: [
    AppLocalizations.delegate,
    GlobalMaterialLocalizations.delegate,
  ],
  supportedLocales: [Locale('en'), Locale('pl')],
)

Text(AppLocalizations.of(context).greeting('Alicja'))

Load and use translations

4
Register AppLocalizations.delegate in your MaterialApp, then read a value with AppLocalizations.of(context).

Why ARB instead of plain JSON?

Both are text-based key-value formats, but ARB adds a metadata convention JSON has no equivalent for: any key starting with @ attaches descriptions, placeholders and plural information to the key of the same name, right in the same file.

If your Flutter setup doesn't rely on that metadata, single-language JSON works too and has an almost identical structure, just without the @key objects.

Same key, two formats
ARB: "signup": "Sign up", "@signup": { "description": "Button text" } JSON (single-language): "signup": "Sign up"
ARB:
"signup": "Sign up",
"@signup": { "description": "Button text" }

JSON (single-language):
"signup": "Sign up"
pub.dev intl package

Good to know

About Flutter and the Intl package

Flutter is an open-source, cross-platform framework from Google. One Dart codebase builds Android, iOS and web apps with the same widget set, which is part of why teams choose it over maintaining separate native apps.

Intl is Flutter's most common localization package. Beyond formatting dates, numbers and currencies, it reads translations directly from ARB files, which is why the format exists in the first place.

Not the only option

Alternatives to ARB for Flutter

Single-language JSON

A near-identical structure to ARB, without @key metadata support.

YAML

Indentation-based structure, easier to read and diff by hand.

CSV

Hand translations to a reviewer or agency as a spreadsheet.

More conversions

Convert ARB to other formats

Free online converter, no account required. Upload an ARB file and download it in the format you need.

ARB to JSON

Drop the @metadata entries and get plain single-language JSON.

ARB to YAML

Move Flutter translations into a YAML locale file.

ARB to Android XML

Reuse Flutter source copy in an Android strings.xml file.

ARB to CSV

Hand an ARB file to a translator as a spreadsheet.

CTA FeaturesGo to Editor

Start translating ARB files

  • Descriptions and custom @key metadata kept as context
  • Plural keys recognized and edited as one string
  • Auto-translation with DeepL, Google, OpenAI, Claude and Gemini
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Frequently asked questions about ARB files

Does SimpleLocalize support ARB metadata like descriptions?

Yes. The description field under a key's @ entry is imported as translator context, and other custom properties such as context or author are kept as key metadata.

How are ARB plurals handled?

Keys following Flutter's zero/one/two/few/many/other naming convention are recognized as one pluralized translation, editable together instead of as separate strings.

Does ARB support nested keys or arrays?

No. Since ARB is built for the Intl package, it only supports flat key-value pairs, the same limitation the package itself has.

Can I export ARB as plain JSON instead?

Yes. Single-language JSON has a similar structure to ARB, without metadata support, and works if your Flutter setup doesn't rely on ARB-specific descriptions or placeholders.