Yep, this isn't a bug it's just how the program works--Cogmind cannot read non-ASCII characters. Note the install instructions say the game path cannot contain such characters either (if it does Cogmind will not start). I should add an explicit note to the manual saying that you it can't read these characters though
Cogmind doesn't use an actual font to display--it just uses a bitmap image, and that image only contains basic ASCII characters, so there's no way to display others. Even if they could be displayed, the internal representation cannot store non-ASCII.
Specific to the manual, I could also try to prevent the game from reading in non-ASCII characters. Currently it
does ignore a certain ASCII character which will crash it (because I use it for a special purpose), but just reads in whatever else you put there.