Damn it... When I lowered the requirement for the ancient languages level from 4 to 3, I didn't notice that I was only checking if the level equals 4(since there was no higher level than 4). By changing only the number in the condition from 4 to 3, I made it so that the game only checks if your level is 3, but not above.
What a stupid way to add a bug.
Anyway, thanks a lot to @Loop_Stratos and @Zekistential for their very detailed feedback. When people first told me they were getting stuck in chapter 8, I was assuming that it was because of that other bug I fixed earlier, and I thought that their versions were just not getting updated properly, lol.
I uploaded a new version (1.41) which should fix the problem. I tested it and it works with level 4 now. Hopefully there will be no more bugs.