def list_locales(self) -> List[Optional[Text]]:
locales = list(self.dict.keys())<EOL>if not locales:<EOL><INDENT>locales.append(None)<EOL><DEDENT>return locales<EOL>
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.