def validate_language_key(obj, key): """Validate all nested "language" key in `obj`. Args: obj (dict): dictionary whose "language" key is to be validated. Returns: None: validation successful Raises: ValidationError: will raise exception in case language is not valid. """ backend = bigchaindb.config['database']['backend'] if backend == 'localmongodb': data = obj.get(key, {}) if isinstance(data, dict): validate_all_values_for_key(data, 'language', validate_language)