Some religions say that they weren't created on earth. For example, Judaism (and spawning religions), as far as i know, believes that at one point, all the languages were 1 language. Then God, to prevent people from getting to powerful, at the tower of babel (take note of the name) jarbled the one language into different languages.
From there, people would take these isolated languages and it would divide into more diverse dialects to the point that we would consider them separate languages. Though, Marc Okrand developed Klingon for the purpose of entertainment, and it differs from codes of english in that it has it's own grammar rules as a platform. Take what you will from whatever religion (if any) that you follow.