I think the point is that Basil is an obnoxious, racist person who's also so cheap he couldn't be bothered to offer Manuel language lessons and proper training.
In a lot of situations, I thought that it's not Manuel's intelligence that's in question, it's just the miscommunication resulting from the language barrier that makes the whole situation funny (e.g. the "un, dos, tres" scene when Basil is trying to tell Manuel that there's too much butter on the trays. It's not Manuel's intelligence that causes the funny situation but the fact that Basil doesn't know Spanish).
Brianwashed!