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.

def list_locales(self) -> List[Optional[Text]]:
        """
        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.
        """

        locales = list(self.dict.keys())

        if not locales:
            locales.append(None)

        return locales