One of the people I met at LAGB had learnt Na'vi, the fictional language of the film Avatar. I haven't seen the film, because it looks abysmal, but I have read about the language. The director, James Cameron (yes, he of Terminator, Aliens, The Abyss and Titanic - you get the idea) wanted a realistic-sounding language for his aliens to speak. And, almost unbelievably, he very nearly managed to ask a linguist. The creator of Na'vi, Paul Frommer, is not actually working as a linguist, but he did do a doctorate in linguistics so kudos to Cameron, I suppose.
So this guy Frommer did a couple of prototype phonologies and Cameron picked the one he liked best, and Frommer went from there to create a small vocabulary and a reasonably complete morphology and syntax. I'm actually quite impressed with how detailed the language description is. I suppose something like Klingon must be more detailed, as there are degrees available in it (allegedly - I can't find any corroboration of that now), but this is the first time I've really looked into any description of a fictional language. Having just written that I'm surprised at myself, as I would have thought as a linguist and sci-fi fan I would have been totally into this, but in actual fact the kinds of books and films that include made-up languages are generally not my cup of tea. A lot of the time they're more the fantasy stuff than the kind of sci-fi I like. Avatar, for instance, isn't sci-fi at all from what I can tell. And then you've got Elvish and all that, but I couldn't even get past the first chapter of the Lord of the Rings and I really hated the Hobbit when I read it (aged about 7, when I was still stubborn enough to get to the end of any book, no matter how dire).
The reason I'm interested now is that I have this vague plan to one day test invented languages and see how they conform to Universal Grammar. I have a theory that there'll be different categories: languages that are made to be used, like Esperanto, ought to conform, in order to be usable and easily learnable, but may not if the creator has approached it more like a logical puzzle (e.g. the classic non-language example of 'reverse the order of words to make a declarative into an interrogative). Languages that are designed for fiction should fall into one of two groups: those that are meant to seem familiar will probably follow UG, and those that are meant to seem 'alien' will probably not (in the same way that enemy languages often have very unusual and difficult-to-pronounce phonologies). Of course, this whole thing will be complicated by the fact that they're all made by humans, who subconsciously or otherwise have UG 'hard-wired' in.
Na'vi seems like it does conform to UG, which fits with it being a 'familiar alien' language - they're not the enemy, these aliens. It also fits with the fact that Frommer knows about other languages and has used bits of grammar and so on from various places, and then added bits of unusual features. So for instance, Na'vi has a dual as well as a singular and plural. That's not so rare. But it also has a trial, which is quite rare (the Learn Na'vi page claims it is, and according to Wikipedia, no natural language has it on nouns, as Na'vi does, only on pronouns. Interestingly it also says that no natural language has quadral marking, though some have paucal, meaning a few, which may be around four).