Which string variables in mysql support utf-8?
You'll have to specify a character set of UTF8 on the table schema.  See http://dev.mysql.com/doc/refman/5.5/en/charset-syntax.html

Depending on your needs you can specify table defaults which then apply to all unspecified text columns (char/varchar/text) or you can specify on a per column level.

You'll also need to have your applications to specify a UTF-8 character encoding.  The specifics on how to do this will depend on the language you are using.