l10n.yaml

# Options used by the localizations tool

## The directory where locale-specific ".arb" message catalog files can
## be found. The output directory will match the input directory if the
#W# `output-directory` option is not specified.
arb-dir: lib/l10n

## Names the template arb file that will be used to check and validate the
## remaining arb files when generating `output-class` and its supporting
## classes.
template-arb-file: app_en.arb

## The name of the localizations class your application will use to lookup
## localized message strings.
output-class: AppLocalizations

## The name of the generated file which will contain the
## class named `output-class`. The file will appear in `arb-dir`
## and the application must import it.
output-localization-file: app_localizations.dart

How can I change the supported-locales by this ?