> Administered by the non-profit Fundació puntCAT under the oversight of ICANN, registrations are available only to individuals and organizations demonstrating use or promotion of the Catalan language and culture.

nyan.cat has a language picker that includes Catalan, even though it just changes the page title.

Anything in the 4XX range is going to be treated as just a regular ol' response, just like 404. (You could serve an entire site with all responses set to status=404, and be fine... other than probably never getting any cache hits) If you don't include a body in the response, the browser might sub in it's own error page, but it will just communicate that the user agent made a bad request.