If you mean the output fields such description, title etc. only supported language is English for now (there’s a backlog item to support more in the future). If you need to get the data in another language, you can query TMDb API using the TMDb IDs returned in the output.

Or if you mean the original language filter in search endpoints, there’re no limitations, as long as there’s a show with the given ISO 639-1 code in the database, it should work just fine.