The Na'vi language was created entirely from scratch by linguist Dr.
Paul R. Frommer.
James Cameron hired him to construct a language that would be easily enunciable for actors to pronounce but would not resemble any human language. Frommer created about 1,000 words. Cameron requested Dr Frommer that the Na'vi language must be entirely new, as it's supposed to be from another planet, and that it should sound "nice" to the audience. Cameron didn't want any additional editing done to their voices and wanted them to sound authentic and not unnatural. Equipped with a vast knowledge of linguistics, Dr Frommer understood what kinds of sounds the Na'vi language would or wouldn't have. Just like "j" and "r" don't exist in Korean, in English, the 'h' sound is unaspirated. In a similar vein, Frommer's conception of the new language totally avoided the sounds of "ch", "th", and "sh". Additionally, Frommer had to decide on the language's syntax -- or rules regarding word order. He came up with his own set of constraints and words to be used in the language of Pandora. The tongue took inspiration from the natural languages of the world to create a totally different spoken form.