FcBool FcUtf16Len (FcChar8 *src, FcEndian endian, int len, int *nchar, int *wchar);
Counts the number of Unicode chars in len bytes of src. Bytes of src are combined into 16-bit units according to endian. Places that count
in nchar. wchar contains 1, 2 or 4 depending on the number of bytes needed to hold the largest Unicode char counted. The return value
indicates whether string is a well-formed UTF16 string.