Babel
io9 has a long article up about creating an alien language. It cites two of the most famous examples of fictitious languages; Tolkein's Elvish, and Marc Okrand's Klingon.
"[Okrand] intentionally violated as many rules of human language as he could. Human languages are unbelievably varied, and there's really no such thing as a true universal, a rule that holds true in 100% of cases. However, there are a lot of features of language sounds, meanings, and grammar that are very common in almost all human languages, and it would be highly unusual if none of these appeared in a human language. Of course, since Klingon isn't a human language, he tried to violate as many of these as possible."
"[Okrand] intentionally violated as many rules of human language as he could. Human languages are unbelievably varied, and there's really no such thing as a true universal, a rule that holds true in 100% of cases. However, there are a lot of features of language sounds, meanings, and grammar that are very common in almost all human languages, and it would be highly unusual if none of these appeared in a human language. Of course, since Klingon isn't a human language, he tried to violate as many of these as possible."