I think I started a topic on this a long time ago, but I can't remember. I was thinking of it today, here are three that came to mind.
1. Nell - I've actually never seen this Jodie Foster movie, but it's supposedly great and she makes up some backwoods version of English or something.
2. Pooty Tang - "Sa Da tay" "On the runnykine" this guy did it all
3. Idiocracy - not exactly a different language, but a very basic and dumbed down version of our precious language here.
Lord of the Rings, Star Trek (thinking Klingon, but there might be a few others), Avatar, Star Wars (again multiple languages).
A Clockwork Orange
Themroc (if it's a language)
Caveman (1981)
The Star Wars Holiday Special has a fair bit of wookie
Black Panther. I believe they use some actual African languages, but I've heard some is fictional as a basis for the Wakandan language. But it's been a while since I've watched it or interviews with the cast.
Must these be usable languages, like Klingon & Elvish, or unusable languages, like R2D2s beeps & boops?