The "Avatar 2" release date will be in December of 2016 and James Cameron recently confirmed that the scripts for the next three installments will all be completed by that time.
During the L.A. Times Hero Complex Film Festival, Cameron discussed the sequels and stated that he has been working on 1500 pages of notes that will be used by four writers to create scripts for the next 3 "Avatar" sequels.
He has hired writers Josh Friedman from "Terminator: The Sarah Conner Chronicles," Rick Jaffa and Amanda Silver from "Dawn of the Planet of the Apes" and Shane Salerno from Armageddon to pen the next 3 Avatar movies. They will use his notes to create a "visually detailed" universe and will take a similar approach to it as if they were adapting a series of novels.
Cameron's inspiration for this method of crafting scripts comes from his time working on the television series "Dark Angel" where he had a "highly collaborative, fun experience." He will begin shooting "Avatar 2" once the three scripts are finished.
He detailed the process thus far explaining how he and the writers sat together for five months, eight hours and day working out every beat of the story for all of the sequels in order to make them connect as one three-film saga. Cameron refused to tell them which part they would be writing until the final day of crafting the story. He describes the writing of Avatar sequels using this strategy as "a really exciting, creative and groundbreaking experiment in screenwriting." He also believes the flow of the three films will be authentic and seamless with it.
"Avatar 2" will be released in December of 2016. A third film will launch in December of 2017 followed by the fourth in December of 2018.