# Regenerating the i18n files The files in this directory are used to generate `stock_strings.dart`, which contains the `StockStrings` class. This localizations class is used by the stocks application to look up localized message strings. The stocks app uses the [Dart `intl` package](https://github.com/dart-lang/intl). To update the English and Spanish localizations, modify the `stocks_en_US.arb`, `stocks_en.arb`, or `stocks_es.arb` files. See the [ARB specification](https://github.com/google/app-resource-bundle/wiki/ApplicationResourceBundleSpecification) for more info. To modify the project's configuration of the localizations tool, change the `l10n.yaml` file. The `StockStrings` class creates a delegate that performs message lookups based on the locale of the device. In this case, the stocks app supports `en`, `en_US`, and `es` locales. Thus, the `StockStringsEn` and `StockStringsEs` classes extends `StockStrings`. `StockStringsEnUs` extends `StockStringsEn`. This allows `StockStringsEnUs` to fall back on messages in `StockStringsEn`.