Ever watched a foreign country movie with its original soundtrack and being forced to read a poor translation at the same time? You should be able to switch forced subtitles off. You will also be able to change the audio language on the fly. You might have heard about this with different words, such as DVD "User Prohibition", UOP, "User Operation Prohibition" or "Prohibited User Operations", a "functionality" that gives the movie's publisher control over your DVD player remote control, deciding which buttons you can use and which you can't. This patch takes that control away from the publisher, and hands it back to you. Don't blame Apple (or your topset player manufacturer) for this, blame the movie industries that enforce this through their license system.
Lastly, this patch also removes the restriction introduced in Mac OS X 10.3.5 where an internal DVD drive is required to run the DVD Player. This patch is localization independent : while the patching tool it is in English only, once applied, the DVD Player will benefit from it, whatever language you use.