Yeah., but this is nothing to do with different languages. He calls them 'Jedi Knights' in the opening scroll because it would be silly to say 'Has secretly dispactched one Jedi Knight and one Jedi Master'. It's like him saying 'has secretly dispatched two soldiers'
But Qui-Gon IS a Master, and when addressing him personally you would always call him that.
But you can say he is also a Jedi Knight, because that's just a generic term for what he is.