// User has 'en' as default locale, but he works from Russia
final fallbackLocale = 'ru';
 
Future<Duration> parseText(String userText) async =>
    // Try to parse user text
    await _parseText(userText) ??
    // Try to parse with 'ru' locale if default parsing failed
    await Intl.withLocale(fallbackLocale, () => _parseText(userText));
 
// This is actual parser
Future<Duration> _parseText(String userText) {
  // ...
}