Assembled by Monica J. Roxburgh:

The test screenings of The Dark Crystal had the Skeksis speaking a language based on ancient Greek and Egyptian, specially created for them by linguist Alan Garner.

As stated by Henson, "My whole approach to this film is visual. I wanted as little dialogue as possible because I believe the story is stronger that way. Dialogue becomes as crutch. If you have all these alien-looking creatures, why should they be talking in English? An early concept was to have the Skeksis just making noises, but in a way you knew what they were saying."*

Gary Kurtz, the co-producer said "The Washington audience thought that they were missing something. Actually, they didn't need to understand the Skeksis' dialogue at those points. The translation of what was being said is really quite banal. The strength of those scenes was instinctively knowing what's going on...The two Skeksis scenes in question were quite long. You had to concentrate. The audience wasn't prepared to do that."*

While the response of test audiences led to the replacement of this language with the English dialogue we know, (as well as several one-liners which father moved the film into "Muppet-territory")*, we can learn a little of this language from the novel The Dark Crystal by A.C.H. Smith.

"'...around the circle, while the chorus of slaves chanted quietly, each Skeksis intoned the same phrase, which then all repeated, in a rite consigning their Emperor's soul, which had never existed, to the protection of a higher being, in which none of them could have tolerated belief...'"
"Kekkon, Kekkon, Yazakaide, Kasdaw."
"Hokkvatta, skaun Skerron."
"Kekkon, Kekkon, Yazakaide, Akura, Teedkhug!"
"Haakhaon!"

The most solemn challenge of the Skeksis, in response to the Chamberlain's premature attempt at claiming the position of Emperor:
"Haakskeekah!" (The challenge, and also cried before each attempt at breaking the stone).
"Pih Tabrokh!" (Uttered by the Ritual-Master at the start of the challenge). "Haakskeekah, Khrokon!" (Cried by the other Skeksis in praise of their new Emperor)
"Khrokon! Khrokon!" (Emperor! Emperor!)

The new emperor is offered a chalice "full of freshly drawn Pod 'vliya', the life-juice that the Scientist extracted from captives when they were first brought into the castle..'"

The Garthim-Master/new Emperor commands the Garithim to release the sack containing (unknown to him), not a Gelfling, but Aughra:
"Ekdideothone."

Aughra insults the Skeksis (in their language):
"Katakontidzeh!"
"Katakontidzeh tekka!"

The Garthim-Master responds to seeing Aughra dumped out of the sack:
"Howtee oo mee Kelffinks." (You aren't a Gelfling).

The Ritual-Master takes over:
"Svaleros ho Kelffinks." (probably: you know where to find it, or you have seen it)
"Kataftheeressthou." (it has to be killed)
"Poostitoc?" (where is it?)
"'...Gelfling gone! Porroh klet! Burn! Ruin!...'" (Aughra's reply)

The Garthim-Master orders Aughra taken to the Chamber of Life:
"Aukra na Rakhash!"

The Garthim-Master orders the Garithm back to their pit:
"Garthim na bullorkhskaunga!"

Aughra insults the Skeksis again:
"Kakofrontez!"

The Garthim-Master sends the Crystal Bats out:
"Kelffinks makhun kim!" (Find the Gelfling!)

The Chamberlain presents the captured Kira to the Garthim-Master, but is cut short by the Ritual-Master, who emphasises his meaning by drawing his talons across his throat:
"Kelffink Krakweekah!"

The Garthim-Master orders her taken to the Chamber of Life:
"Kelffink na Rakhash!"

The Garthim-Master is concerned with the other, missing, Gelfling:
"Kelffink cho tenkha. Vo olk Kelffink ulls?"

The Ritual-Master commences the Great Conjunction ceremony:
"Khavekh, Khavekh, Orkhasstim."

The Garithm-Master notices the unexpected company:
"Kelffink!" (he notices Jen)
"Teen Kelffinkim!" (he notices that there are TWO Gelflings)

After Jen drops the shard, the Ritual-Master realizes how close the prophecy was to being fullfilled and warns:
"Klakk smaithh Skwee Kreh!"