wctrans_t wctrans_l(const char *property, locale_t loc);
wctrans_l constructs a value of type wctrans_t that describes a mapping between wide characters identified by the string argument property in locale loc.
If property identifies a valid mapping of wide characters in the locale loc, wctrans_l returns a nonzero value that is valid as the second argument to towctrans_l; otherwise, it returns zero.
The only mappings supported are "tolower" and "toupper".