Man, when I saw that ZTranslate was a thing, and that this game was the first target, I didn't know you were going to play it so soon. I actually spent a quite a bit of time making my own translation, working with the game files instead of OCR, but I got heavily sidetracked along the way. I do still intend to complete it.
About that issue throwing the pie at Qualbert: That's strange, I never encountered it in the couple of playthroughs I did.
I do have a bit of nitpicking to do:
Collie is short for "collaborator". Hellami (the woman with the green shirt) explains this in the first conversation you have with her. (I honestly don't know if that was a joke on your part and I just didn't get it, or if it was an oversight.)
The origin of the light is explained in the companion booklet "The Book of Veldoor" already mentioned in this thread. Tl;dr: it's coming through crystals in the cave ceiling. If you inspect the book in-game, the game will actually make a snarky remark:
I've made a rough translation, which I was gonna finish later, but I guess I can put it up here now. I'll try to polish it up in the next few days.
"Ginbart is fine, and he knows a lot more than you do." - That's a translation error. The original line went more like "Ginbart is all right, and he knows a lot more than you'd think."
If the guys at the inn in Wahringen walk out or refuse to talk to you, the game isn't softlocked. For the low price of 3 folints you can go back to Berg-Wolkenheim and talk to Ginbart. He's got some connections and can pass a message, which will make them return.
The place with the static waterfall and the big dragon statue is called "Mindhoor". The dark side of the cave world is called "Maldoor".
"Are you healthy and fit?" - I would also consider that somewhat of a mistranslation. I would have gone with "Did you come back in one piece?", or simply "Are you all right?", or something like that.
But most importantly, of course: Maomi doesn't have to dump you at the end! The game has a, sort of, relationship status variable for Maomi, which increases, when you pick choices the game considers proper, and decreases when you pick the wrong choices. One wrong choice, for instance, is asking "How's Gusmar?" instead of asking "How are you?" when taking the three mirrors back to Sekamidoor. Another one is suggesting for her to leave the Cave World with you, instead of staying and finding the gleaming crystal. I don't know all the relevant conversation options, so I've not gotten it legitimately, but editing the byte at 0x465B to 0x0A and the one right after that to 0x00 in the save file should get you the good ending. (I've attached a save file where this has been done.)
About the card game: Yeah, that was weird. I've played that as well and it didn't have any multiplayer option, just a big singleplayer map with a lot of AI opponents to battle. And it's grindy as hell, unless you found the glitch, which allowed you to sell the same card infinitely many times. (That made the game a lot more fun.) It also has a strange campaign mode, which plays a bit like a text adventure, except with battles, which are fought using the card game. There is also an editor, which can use to create your own campaigns, but I haven't come across any fan creations.
The card game is based on the Höhlenwelt-Novels written by the game's writer, Harald Evers. (If you watch the credits again, you'll see his name more than one time.) My impression was that while they started out with some interesting concepts, they got pretty boring by the second book. There were going to be 3 "cycles" with 4 novels each, but Evers was only able to complete eight novels, as he died of a heart attack in 2006, at only 49.
One last thing: The game didn't just use CD audio, it also came with some MIDI tracks. So in case anyone feels like giving some new life to this music,
I've attached the sound files I was able to extract.
Oh, yeah, I forgot. The episode was great. I haven't laughed that hard in a while. I guess part of the reason was that I spent so much time with the game myself. I especially liked your comment about the "semi-insane infinite looping conversations".
The Book of Veldoor.zip