Zhiyi Zhang (@zhiyi) commented about dlls/bcp47langs/main.c:
+#include <hstring.h> +#include <winstring.h> + +#include "wine/debug.h" + +WINE_DEFAULT_DEBUG_CHANNEL(bcp47langs); + +DWORD WINAPI GetUserLanguages(char delimiter, HSTRING *user_languages) { The prototype is probably HRESULT WINAPI GetUserLanguages(WCHAR delimiter, HSTRING *user_languages). So the return value should be S_OK. You can add some parameter tests, for example, by passing NULL to user_languages and see if the return value is something like E_INVALIDARG.
For delimiter, it's most likely a WCHAR. This can be verified by passing a Unicode char to delimiter and check the result string. And move { to a new line. Add a newline after variable declaration. -- https://gitlab.winehq.org/wine/wine/-/merge_requests/6131#note_81017