This page outlines information about DVD playing with LinuxMCE.
As the Xine Player is used to play DVD, most of the settings can be changed in the $root/etc/pluto/xine.conf configuration directory. $root points either to the root directory of the Core/Hybrid, ie. the file is /etc/pluto/xine.conf, or one of the diskless orbiters. The diskless orbiters file is /usr/pluto/diskless/$orbiter-id/etc/pluto/xine.conf.
To change the default DVD language from the current english, locate the line
remove the hash and change it to the preferred language. For example, changing it to german, the line looks like this: