Hello @someone,
First of all, according to the WM_CHAR message,
The WM_CHAR message uses UTF-16 (16-bit Unicode Transformation Format) code units in its wParam if the Unicode version of the RegisterClass function was used to register the window class. Otherwise, the system provides characters in the current process code page, which can be set to UTF-8 in Windows Version 1903 (May 2019 Update) and newer. For more information, see Registering Window Classes and Use UTF-8 code pages in Windows apps.