I understand you made
one subtitlefile in
two languages?
Such bilingual subtitle should display no different than a subtitle in just one language.
If you wish to be able to choose/switch language easily and in a nice way, you should create two subtitle-files and use a .bsi (=ini) file.
Unless you are a more experienced user, I would say let
Matimott's utility "Inimaker" do the work for you. You can download it here:
http://www.ifrance.com/kpage/pages/down.htm
(You could of course also switch language in a less nice way: just load the subtiltle file in the other language while the movie is running.)