def METHOD_NAME(self, source_langs: bool) -> list[Language]:
    """
    Reverse-language is supported as the only target language.
    :param source_langs: See documentation on TranslationService.
    :return: See documentation on TranslationService.
    """
    if source_langs:
        return Language.query_all()
    else:
        reverse_lang = Language.query_by_code(REVERSE_LANG["lang_code"])
        if reverse_lang is not None:
            return [reverse_lang]
        raise Exception(
            f"Test-language is not found in database with the code '{REVERSE_LANG['lang_code']}'."
        )