To have full UTF-8 support you need to edit the includes/classes/database/mysql.php file and add the following code:
$this->query("set names utf8");
This line goes at the end of the connectToDb function.
Another change that may need to be made is to add the following line to the connections/classifieds.php file:
ini_set('default_charset', 'UTF-8');
And finally in the language file add:
setlocale(LC_TIME, 'de_DE.UTF8');
Replace the de_DE with your locale setting.