"In the sinister horror stories of Arthur Machen and HP Lovecraft, Aklo is the language set down by the Serpent races 1.5m years ago, possibly dictated to them by the Old Gods. Its main use is in incantations designed to summon Cthulhu, Yog-Sothoth and other evil cosmic entities from the nether regions, but lines such as “Ph’nglui mglw’nafh Cthulhu R’lyeh wgah’nagl fhtagn” have the secondary effect of making your computer’s spell check explode."I found the spell check line kind of amusing, but your mileage may vary. The other languages they mention are Klingon, Newspeak, Nadsat and Elvish. Hey, what about Cityspeak from Blade Runner?
(from The List: Five fictional languages)