Thanks for finding that. We switched from ANSI in 0.2 to UTF-8 in version 0.3, so it must be related to that.
Just to confirm, if you log in with the non-latin character username, not having an appdata/Bitcoin directory yet, and run Bitcoin and let it create the database from scratch, does it work or not?
BitcoinTalk
bitcoin 0.3 win64 - broken access to APPDATA if non-latin characters in username
Re: bitcoin 0.3 win64 - broken access to APPDATA if non-latin characters in username
I think I see where the problem is. Coincidentally, I recently coded a replacement for the function in question which should fix it. It's not enabled yet, but in the SVN version it prints a debug message in debug.log showing the new directory value and old value for comparison.
Re: bitcoin 0.3 win64 - broken access to APPDATA if non-latin characters in username
I tested this with a non-lower-ASCII account name on XP and confirmed the bug, then tested that the new GetDefaultDataDir fixed it. This change is revision 102 of the SVN.