code: func Tfunc(languageSource string, languageSources ...string) (TranslateFunc, error) {
  	tfunc, err := defaultBundle.Tfunc(languageSource, languageSources...)
  	return TranslateFunc(tfunc), err
  }
docs: // Tfunc returns a TranslateFunc that will be bound to the first language which
  // has a non-zero number of translations.
  //
  // It can parse languages from Accept-Language headers (RFC 2616).