const Locale(String languageCode, String countryCode)

Creates a new Locale object. The first argument is the primary language subtag, the second is the region subtag.

For example:

const Locale swissFrench = const Locale('fr', 'CH');
const Locale canadianFrench = const Locale('fr', 'CA');

Source 

const Locale(this.languageCode, this.countryCode);