According to Robert Wise's commentary in the Director's edition DVD, it was Gene Roddenberry's idea to have the Vulcans speak their own language. [Wise, Robert. Star Trek: The Motion Picture Directors Edition [Disc 1]. Special features: Commentary] The translation into Vulcan was made by actor James Doohan. Doohan observed the actors' lip movements and created new vocal "sounds" for them to dub over their original English. According to the DVD commentary of the film Star Trek II: The Wrath of Khan, actors Leonard Nimoy and Kirstie Alley, portraying Spock and Saavik respectively, also spoke their lines in English, and later dubbed in Vulcan that corresponded with the movements of their mouths in the scene. Marc Okrand on Klingon. YouTube. May 2, 2012. Archived from the original on December 11, 2021. Retrieved September 26, 2015.
Michael, Okuda (1999). The Star trek encyclopedia : a reference guide to the future. Okuda, Denise., Drexler, Doug. (Updated and expanded ed.). New York: Pocket Books. p. 550. ISBN0671034758. OCLC42837231.
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According to Robert Wise's commentary in the Director's edition DVD, it was Gene Roddenberry's idea to have the Vulcans speak their own language. [Wise, Robert. Star Trek: The Motion Picture Directors Edition [Disc 1]. Special features: Commentary] The translation into Vulcan was made by actor James Doohan. Doohan observed the actors' lip movements and created new vocal "sounds" for them to dub over their original English. According to the DVD commentary of the film Star Trek II: The Wrath of Khan, actors Leonard Nimoy and Kirstie Alley, portraying Spock and Saavik respectively, also spoke their lines in English, and later dubbed in Vulcan that corresponded with the movements of their mouths in the scene. Marc Okrand on Klingon. YouTube. May 2, 2012. Archived from the original on December 11, 2021. Retrieved September 26, 2015.