A comment on this SE question stated:
Klingon is a real Earth language, but it's only heard in the second movie and never shown printed.
I couldn't find any references to that.
Was Klingon used in any of the Star Wars movies?
Yes there was. In Star Wars Episode 3: Revenge of the Sith. Anakin looks over to a red view screen when the senator arrives. The text symbols on the screen is Klingon. As an avid Trek fan, I couldn't miss it. It's about 1:40 minutes into the movie when he is on the volcanic planet.
Upper part of the screen: