The problem is that subsonic requires the correct language/encoding set when run. It seems that it needs UTF-8 set as encoding.
To do this, modify the start-script of the subsonic-server (usually /usr/share/subsonic/subsonic.sh) and add the following line to the beginning:
then restart the daemon. The web-interface should now display everything correctly and Clients like iSub on the iPhone should be able to play all songs aswell.