Forced subtitles

[Ghitulescu]

There are millions of forced subtitle threads according to google, I have read a few hundred which I considered to be the most relevant, still found no true information about this. And yes I do not have the "bible".

The almost "copy/pasted" information goes like this - forced subtitles are those subtitles that appear when aliens speak

What I want to know is the way they really really work in a DVD player.

* For instance, assuming I am a German national, what forced subtitles are displayed, the English ones or the German ones? Similarly for French and other non English and/or non Alien nationals On which basis the player chooses which one to display? And in case of conflicting requirements and settings, which are the prevailing ones?
* Can they be fully inactivated? Can they be activated (by hand)? Taking for instance a WW2 movies, where German soldiers speaking German are forcibly subtitled: no use of English forced subtitles, unless one believes conspiracy theories

Thank you.