There’s really no other way to say it: language creation in fantasy and sci fi has become a fad. Not that that’s a bad thing…
Tolkien did it “first,” and did it right–I went through a phase where I spent hours in my orthodontist’s office (horrible beast that he was) pouring over notes and vocab lists in an attempt to learn Quenya, but ever since having my braces removed and starting courses in Ancient Greek, Latin, French, German, and Japanese, my interest in his language has devolved from a rabid fascination to a healthy respect: I didn’t really have time for it anymore, so I decided to prioritize and settle for nodding pleasantly at it from a safe distance.
Other authors have flirted with it: Christopher Paolini’s Inheritance series is riddled with standalone vocabulary and occasional incantations and short conversations, but we never get a stark view of the scope. There’s not enough of it to lose the less language-crazy reader, but there’s also not enough there to incite slavering fans to write unofficial grammar books, either.
Avatar did a nice job with Na’vi, I thought. Pretty language (it wasn’t even Latin-based!), lots of influences, lots of plain-old ingenuity. It’s one that I wouldn’t mind brushing up on for a convention, although, I don’t think I’ll be taping on pointy ears and a tail for the full effect.
At the risk of shamelessly copying these fine examples, I’m currently brewing up a language for my own story, Unfit: Xhardúrin will be based largely on Persian/Farsi phonetics (sigh, it’s like running water and music combined…) and I’m taking from a hodgepodge of grammatical sources as well. Blended sounds such as those common in Persian do not lend well to agglutinative construction (my favorite) like what you might find in Japanese (the sounds and syllables are so square and set that they can essentially “stack” end to end without sounding clunky or flat out turning into mouth-acrobatics), but I may work some in just because I like it so damn much.
For now, the sounds of Xhardurin!