You can set the system codepage to CP_UTF8 since Win 10, I guess, although IIRC it still doesn't work for input. But a) there is a lot of programs using A() functions that don't expect that and break in subtle ways, e.g. DBCS-encoding-aware programs suddenly break because they don't expect a codepoint to span for more than 2 bytes; b) most of the sanely written programs either use UTF-16 explicitly, or use UTF-8 internally and convert between UTF-8 and UTF-16 before/after calling W() functions.