Does something like in attached patches work for you? [0001-msvcrt-Print-FIXME-when-WideCharToMultiByte-fails-in.patch](/uploads/56d6b0ad6b6326079be88e963c5dbf57/0001-msvcrt-Print-FIXME-when-WideCharToMultiByte-fails-in.patch) [0002-ucrtbase-Fix-CP_UTF8-handling-in-_toupper_l.patch](/uploads/6972e474ae498c53915abcf7d32541b5/0002-ucrtbase-Fix-CP_UTF8-handling-in-_toupper_l.patch) [0003-ucrtbase-Fix-CP_UTF8-handling-in-_tolower_l.patch](/uploads/7bcb608dc4db056c1e7b3d1695eb5484/0003-ucrtbase-Fix-CP_UTF8-handling-in-_tolower_l.patch) [0004-ucrtbase-Fix-case-mapping-and-ctype1-tables-for-utf8.patch](/uploads/7de0039c3d623c7d53792e5085add570/0004-ucrtbase-Fix-case-mapping-and-ctype1-tables-for-utf8.patch) -- https://gitlab.winehq.org/wine/wine/-/merge_requests/8198#note_105375