What bothered me the most about the film, as it did anyone who understands language, is that Grace's method of learning to communicate with Rocky is NOT HOW TRANSLATIONS WORK.
You can't just substitute words. Even if you ignore the problem that every word has a half dozen meanings depending on context, grammatical structure has a ton of variety even among human languages. Even if you take a human language like Japanese and you attempt word substitution you get gibberish out the other end.
The book answers this with two or three sentences, that could have easily been a throw away line in the movie.
Rocky's species use sound for everything, so naturally their brains are far better at processing language than ours. Rocky picked up English with little effort, and is intentionally speaking his own language wrong for Grace's sake.
Grace isn't the only person attempting to learn a new language. Rocky did it first, and is helping his less intelligent human counterpart. From Rocky's perspective he is mixing up his own language's grammar and misusing words to compensate for Grace's poor memory.