code: func (b *Bundle) supportedLanguage(pref string, prefs ...string) *language.Language {
  	lang := b.translatedLanguage(pref)
  	if lang == nil {
  		for _, pref := range prefs {
  			lang = b.translatedLanguage(pref)
  			if lang != nil {
  				break
  			}
  		}
  	}
  	return lang
  }
docs: // supportedLanguage returns the first language which
  // has a non-zero number of translations in the bundle.