I disagree that the moniker “most extensive” should be applied to Dorothy Jones Heydt’s language. It's true that it is well know and some of her vocabulary survives today. Her work is deserving of tremendous respect. I’ve done a LOT of research on this as of the Fall of 2010 and I have to give the title of “most extensive” to Mark R. Gardner’s Golic Vulcan series. The vocabulary is well over 12,000 items (almost unheard of for any SF-related constructed language) and the grammar allows for very thorough, descriptive translations. To see examples of Vulcan in “everyday use” visit Korsaya.org. To learn the language from square one, I suggest the Vulcan Language Institute Reclamation Project at STOGEEK. The full online dictionary (of multiple dialects including Golic Vulcan) is online at the VLD.
Marc Okrand worked on the few lines of ADR dialogue in the film STII WoK between Spock & Saavik (Kirstie Alley) and wrote the lines for Robin Curtis (again as Saavik) in STIII SfS. Curtis actually spoke the lines live. ADR was not a factor. However, he did not write the few words spoken by Dame Judith Anderson later in the same film. He also created the brief dialog between T’Pol and her mother in the TV episode ENT::HOME (Oct., 2004). I’ve learned these details directly from Dr. Okrand via personal correspondence.
Most of the words created for the first three motion pictures are incorporated into Golic Vulcan.