https://bugs.winehq.org/show_bug.cgi?id=54424
--- Comment #1 from François Gouget fgouget@codeweavers.com --- So the failure results from interpreting a string in the 932 code page using the 1252 codepage:
L"\4e00\4e8c\4e09" -- CP_ACP --> "\x88\xea\x93\xf1\x8eO" L"\4e00\4e8c\4e09" -- 932 --> "\x88\xea\x93\xf1\x8eO"
"\x88\xea\x93\xf1\x8eO" -- CP_ACP --> L"\4e00\4e8c\4e09" "\x88\xea\x93\xf1\x8eO" -- 932 --> L"\4e00\4e8c\4e09" "\x88\xea\x93\xf1\x8eO" -- 1252 --> L"\02c6\00ea\201c"
Where that last line corresponds to the unexpected result.
More specifically, the issue is that CP_ACP is 932 (from ThreadUILanguage) but WM_CHAR interprets the characters using the user locale's default code page, 1252 in the TestBot's mixed locales configuration: