MB_CUR_MAX - maximum length of a multibyte character in the current locale
The MB_CUR_MAX macro defines an integer expression giving the maximum number of bytes needed to represent a single wide character in the current locale. This value is locale dependent and therefore not a compile-time constant.
An integer in the range [1, MB_LEN_MAX]. The value 1 denotes traditional 8-bit encoded characters.
POSIX.1-2001, POSIX.1-2008, C99.