Is this just a demo or is the game still in active development? Is the translation for the entire thing?
The game is complete, but the author has plans to come back and release another chapter later. The translation is mostly complete, in that when you get to the end it becomes MTL, because the person doing the translation hasn't finished with the edits there, so you just get raw MTL. Good quality translation up to that point, and by then you know enough that interpreting the MTL isn't overly difficult, though I'll definitely play it again once the translation is done.
Also the list of things the creator is doing that was posted above includes an english translation. Who knows what the quality of it will be, but that is an option that will presumably arrive at some point.
On a completely different note, I finished the BAD END dungeon the other day. ... holy shit did that get fucking hard at the end. I was playing it on Very Easy, where you get three different save points per level, and I while I managed to bull through it after a few days, I don't want to imagine what it would be like on easy where there is just one save point per level, or on normal ... where you get no save points at all.
Trying to go through the entire dungeon in one go, especially when if you don't remember perfectly what you have to do to solve each part, while at the same time trial and erroring the new stages, would be an utter nightmare. There are parts where if you don't run forward right out the gate you are screwed, and parts where if you do that you are screwed, and if you messed up the order at any point, you're boned, to say nothing of not making a single mistake in each level as you go. That's one of those, theoretically doable, but in practice I doubt any one has the patiance, even if they used the very easy mode to learn the steps before trying their no hit run. To anyone who somehow succeeds in completing it on a difficulty besides very easy, I salute you.