I never played a Eushully game before so I don't know much, but I'll try to help.

If you're certain you already changed the timezone, time format, location and language for unicode program to Japanese, then the problem may be the font itself. Does this only happen to Eushully games? Do you know what Eushully's default font is? Maybe some of Windows' supplemental fonts were lost during the update and that was one of it?

If you're sure that the font is still there, Do you have a sample screenshot of that error?