Subject: Klingon
OK...this is cool. Duolingo actually offers Klingon. Just stumbled on it. I know a few basic words (yes, I'm a Trekkie). But Duolingo thinks they can make a person fluent in Klingon. I just did one lesson for fun. Maybe I'll do a few more. Though my Star Trek convention days are long behind me.

I always found it amazing that they constructed an actual language to use in the Star Trek films. I read an article many years ago that they actually built a language with rules (as any language has), though the vocabulary was restricted initially to the sentences they needed for the films. To my knowledge, it is still limited in terms of vocabulary, and it relies heavily on context with the vocabulary it already has. Maybe they've expanded it a bit? Dunno.