code: def list_locales(self) -> List[Optional[Text]]:
          
  
          locales = list(self.dict.keys())
  
          if not locales:
              locales.append(None)
  
          return locales
docs: Returns the list of available locales. The first locale is the default
          locale to be used. If no locales are known, then `None` will be the
          first item.