Flutter .arb

Flutter .arb (Application Resource Bundle) file format is the Native format for Flutter applications. It not only stores the localization keys and values but also the metadata about the key like description and placeholders. Flutter's message format is very similar to the ICU Message Format, but it does not store the parameter types in the actual ICU string but in the metadata.

en.arb

{
  "user_settings_password": "Password",
  "user_greeting": "Hello, {user_name}!",
  "@user_greeting": {
      "placeholders": {
          "user_name": {
              "type": "String",
              "example": "Peter"
          }
      }
  },
  "dogs_count": "{count, plural, one {I have {count} dogs.} other {I have {count} dogs.}}",
  "@dogs_count": {
      "placeholders": {
          "count": {
              "type": "int",
              "format": "compactLong",
              "example": "1"
          }
      }
  }
}

As you can see in the above example, the message parameters don't contain the type information, but the metadata does. Another important difference to the standard ICU Message format is that the # symbol in plural form isn't replaced with the actual number, so you have to repeat the placeholder again ({count} in the example above).

Metadata Import

When importing the .arb file, the metadata are stored in the Custom Values field of the key. e.g. For the user_greeting key, the metadata will be stored this way:

Custom Values

{
  "_flutterArbPlaceholders": {
    "count": {
      "type": "int",
      "format": "compactLong",
      "example": "1"
    }
  }
}

To see the imported metadata, open the Key Edit dialog by clicking the key name in the Tolgee platform and go to Custom Values tab.

Read more about Custom Values here.

When exporting, Tolgee exports to the .arb file with this metadata when provided. The parameter types provided directly in the ICU Message Format in Tolgee are ignored. For example, translation Today is {date, date}, will be exported to the .arb file as Today is {date}. To provide the parameter type, you need to provide the metadata in the Custom Values.

The MessageFormat and placeholder conversion

Tolgee doesn't convert Flutter placeholders to ICU placeholders because the Flutter Message format is effectively a subset of ICU. When exporting to .arb, Tolgee discards the type information from the ICU Message Format, so it's a valid string for Flutter MessageFormat class.

Importing / Exporting in general

To read more about importing and exporting with Tolgee, continue to import section or export section.