Klingon is not based on any single human language.
Marc Okrand, the creator of Klingon, is a trained linguist. When he created the language he used his linguistic knowledge to pick all the rarest aspects of human languages and combined them together to create the Klingon grammar. He also purposely broke a number of human linguistic rules in order to make the language more alien.
The vocabulary is based on the sounds that James Doohan created for Star Trek The Motion Picture. Okrand took these sounds, added a few more rare sounds (a number from dead native American languages) and then created a word list.