I also have the same problem with polish characters in path where program is installed
C:\temp\jakas nazwa: is OK
C:\temp\jakaś nazwa: is not OK
I have made a workaround - user cannot install program in folder with special chars, but it is not satisfiying me
I just tried this and I saw the same thing, even with 3.9 so I'm going to look at this right now. It should work, I've seen it work with other characters. Very odd. I'll post back here when I find out what's going on and I have a fix for you.
Okay, I think I have a fix. I tested with your path as well as paths with chinese, korean, hebrew, arabic and russian in them (gotta love google translate) and they all work. If you send an email to firstname.lastname@example.org I'll put you on the 3.9 beta list.