Is knowledge of foreign languages per se helpful for graduate applications? Would this be considered at all, or is this not even important? I am not talking about fields which have these foreign languages as their object of study, or where it is obvious that the language would help (if I were to study French Literature, knowledge of French would obviously be important).

But what about fields which are primarily English, so say I want to do my PhD in Political Theory. There are probably a few articles in foreign languages I could make use of, but English seems just fine. Would knowing a foreign language still be an advantage, or not really?
I'd say that if the programme(the course) does not include or require any other language than English, the knowledge of the other languages "might be"(so it does not have too much chance) taken in consideration. This probably also depends on in which country you are going to study your PhD. But they focus on mostly the subjects related to the course, and the degree you have graduated with. But I think it would help you getting a job after your studies. After all, if you learn a new language you don't lose anything but gain knowledge of a different culture (unless you consider the time spent for learning is lost and was not worth).