If you want to add support for a new character set that includes multi-byte characters, you need to use multi-byte character functions in the ctype-MYSET.c source file in the strings directory.

The existing character sets provide the best documentation and examples to show how these functions are implemented. Look at the ctype-*.c files in the strings directory, such as the files for the euc_kr, gb2312, gbk, sjis, and ujis character sets. For MySQL 4.1, take a look at the MY_CHARSET_HANDLER structures to see how they are used, and see the CHARSET_INFO.txt file in the strings directory for additional information. For MySQL 4.0 or older, look at the CHARSET_INFO structures.