If you write cross-platform software, the easiest solution is usually to pretend everything’s Unix. You’ll hit some problems (e.g. assuming all filesystem APIs always use UTF-8 will bite you on Windows, which switched to UCS2 before UTF-8 or UTF-16 were invented, so now uses UTF-16 for Unicode-aware functions as that’s the one that’s ABI compatible with UCS2, and passing UTF-8 to the eight-bit-char functions requires you to opt into that mode explicitly), but mostly everything will just work. There’s no XDG_CONFIG telling you to put these files anywhere in particular, as Windows is Windows, so most things use ~ as a fallback, which Windows knows to treat as %USERPROFILE%.