https://bugs.winehq.org/show_bug.cgi?id=51327
--- Comment #5 from Rafał Mużyło galtgendo@o2.pl --- Also, on a semi-random note, it seems update_font_code_page in win32u was written based upon how things are supposed to work, not how they actually work in wine (bugs like my bug 42606 might be a result of that).
Just sticking with CP_ACP would likely be more consistent.