Move inclusion of stdint.h to integer.h.
Use wchar_t instead of WCHAR for Unicode characters.

WCHAR appears to be an unsigned short int (16-bit), while wchar_t is an int (32-bit).
Wrap quoted text in _TEXT() macro so we get wide-character strings when _LFN_UNICODE is enabled.

Still no swprintf in Arduino though, which makes generating file names a little difficult.