While researching what sci-fi conlangs there are, I think I discovered why there are so few in written novels - not enough space in the book for the dictionary. Riksprok took up half of this book.
They are rare if you look at the percentage of books that could have put together a complete fake language for their aliens. Most fake languages in fiction are character and place names.
The authors that go beyond that, don't always do a sophisticated job. Mando'a is pretty much a relex of English, i.e. English with all the words replaced.
New Speak was a rough sketch of a language that was never finished. Fremen was started by Frank Herbert, but was subsequently developed as Chakobsa in the "Dune Encyclopedia". [Lapine]3 is an example of a language that seems to have been developed more by the fans afterwards.
Yeah, they're movie languages, but Na'vi and Klingon are the current Xeno-languages with a fan base and users that are competent to read and write it.