SMF forum is a great software, however, sometimes it needs tweaking when it comes to UTF-8 support.
The below is a very quick fix. Open SSI.php.
global $smcFunc, $ssi_db_user, $scripturl, $ssi_db_passwd, $db_passwd, $cachedir;
Add just two lines below and save:
mysql_query('SET NAMES UTF8', $db_connection);