Is knowledge of foreign languages per se helpful for graduate applications?
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).