In line 722-724 in inc/auth/mysql.class.php, the mysql character set is set to some configured value (this->cnf['charset']). This leaves the impression, that the character set of the mysql database/tables/columns should be given during configuration. However, with the mysql command "set character set" the character set of the client is given to the mysql server, so that the server can deliver adequately to the client.
Therefore lines 722-724 should be replaced with:
mysql_query('SET CHARACTER SET "utf8"');
since the character set of Dokuwiki is fixed to utf-8. This statement seems to be valid for all mysql versions (4/5/6).
Alternatively, a line
$conf['auth']['mysql']['charset'] = 'utf8';
must be added in conf/mysql.conf.php, if the database is NOT delivering in utf-8 (which is a weird thing to do).
This report seems to be related to Bug Report 764.