Like any story worth telling, the history of the Klingon language begins with improvisation. Some reports—including the DVD commentary for Star Trek: The Motion Picture Director’s Cut—maintain the genesis of the language rests with James Doohan (who played Montgomery “Scotty” Scott on the original show) and the film’s associate producer Jon Povill. The two had a meeting where they established a few basic words the aliens would utter throughout the movie. Doohan recorded the words for veteran Trek actor Mark Lenard, who portrayed a Klingon captain in the film. Lenard transcribed the words phonetically and practiced them to nail the delivery of his lines in the film. Doohan and Povill didn’t develop the language further. That honorable duty befell another man who wouldn’t enter the picture until Wrath of Khan’s editing phase.
Enter legendary linguist Marc Okrand, the creator of the Klingon language.
You can even learn it on Duolingo!