Simplify the following text for a Grade 6 native English-speaking person.
Original: Frommer expanded the vocabulary further in May 2009 when he worked on the Avatar video game , which required Na ` vi words that had not been needed for the film script and thus had not yet been invented . Frommer also translated into Na ` vi four sets of song lyrics that had been written by Cameron in English , and he helped vocalists with their pronunciation during the recording of James Horner 's Avatar score .
Simplified: The first Na ` vi words were made by the professor Paul Frommer in 2005 for the film .