Dr. Marc Okrand developed a Klingon language for one of the Star Trek movies, and it took off with the Klingon fanbase. I think there are more Klingon speakers than Esperanto speakers nowadays.

Star Wars, on the other paw, made liberal use of existing Earth languages mixed with gibberish.

The original Land of the Lost had two created languages.

It's jokingly said that Tolkien had created so many languages for fun that he finally felt the need to write a story or two to hang them off of.

Making languages is second only to world building in sci-fi (and there's just as much of a spread in how well it's done).

Having said all that, I'd like to point out that I don't expect to be picking up more than a word or two -- if that -- of Na'vi.