TheBoost said:

I heard once that Henson wanted the Skeksys to speak a foreign language, and we'd just have to make inferences as to what they were saying, but the studio balked.

There's footage of that on all the releases of the films - single DVD, 2 disc DVD and BluRay. The BD also has an introduction by the writer explaining that when they decided the foreign language idea wasn't working, he spent an entire weekend with Henson going through the film making notes as to mouth movements and timings of the Skeksis scenes so they could figure out new English language dialogue that would sync up.

Side note - only the single DVD edition includes an isolated music track. What's a simple freeware program that can rip the audio track so I can make myself a soundtrack CD?