Yep, you got it! If someone already knows the language spoken, no translation is needed and it'll be just like normal; and like you said, when an unknown language is spoken, the person understands the meaning without initially realizing it's a foreign language. If a person wants a word to not be translated and heard in the original language, they just have to have the intent.

So yes, he can teach people tyrannosaur growls! Spread the language of the great dinos~