SilcUInt32 silc_utf8_w2c(const SilcUInt16 *wide_str,
                             SilcUInt32 wide_str_len,
                             unsigned char *utf8, SilcUInt32 utf8_size);

    Converts UTF-8 wide character string into UTF-8 binary string into the
    `utf8' buffer of size of `utf8_size' in bytes.  Returns the length of
    the encoded UTF-8 string in bytes or 0 on error.

    If there is extra space in `utf8' this will NULL terminate the string
    automatically.