setlocale(LANG, "ja_JP.UTF-8");
setlocale(LC_CTYPE, "ja_JP.UTF-8");
char* utf8 -> mbstowcs -> wchar_t* wcs
wchar_t* wcs -> wcstombs -> char* utf8
https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/setlocale-wsetlocale?view=vs-2017
https://mgng.mugbum.info/1014