There are two ways to solve this:
1. For Apache, open your httpd.conf and inside your host definition put this line:
php_flag default_charset UTF-8
Then restart Apache.
2. A better way is to open the file main.inc.php and add the following line just before session_start():
ini_set('default_charset','UTF-8');
This 2nd solution could, perhaps, be included in the sources to prevent this problem in the future. Btw, don't forget to edit and save the file(s) using UTF-8.