I do some incantations or chanting in my mind and they work just fine. What matters is your intent, wish, preparation, mind set, etc.
I don't think being deaf could be a problem - in magic you work with energy and for her (energy) there is no difference in language.
What I could predict, that chanting aloud could help dealing with energy. But that's probably it.
If you believe that chanting in mind will work - than it will ;)