[quote=@prettydrops]
Just trying to stay consistent with posts and world building! little stuff like this can cause plotholes and confusion from my end if I'm not careful xD
[/quote]

I had the professor using sign language because those Pokemon are still very young, similar to how babies can understand and communicate through simple sign language before they can speak. 

Pokemon in this RP, all have a human level intelligence. Only, they're brains stop maturing at about teenager level inelligence (unless the Pokemon is known to be smart, such as most psychic types.)

So as far as understanding human speech, they can all learn, just some faster than others. Obviously they can't speak back though, as they don't have the right vocal cord set up. (Again, this doesn't include psychic types that can communicate through telepathy.)

In the end, I just ask that you use your best judgement. 

Hope that helps. Thanks!