Are foreign language requirements beneficial for Physics, Math and Chemistry PhD students in North America?
Readers, who learned foreign languages for their PhD, do you remember
  any case where you benefitted from reading a foreign language
  paper/book/...


I'm a (pure) mathematician in the US, and I've literally benefited hundreds of times from being able to read mathematical French. Not only are there great papers in my area that are being published in French today, but a huge proportion of my field's seminal papers were written in French during the twentieth century. (I know that for people working in other areas of pure math, German plays a similar role.) In fact, I find it very hard to believe that someone would be able to have a successful research career in various areas of pure math without being able to read papers in a language other than English. Certainly such a person would be at a huge disadvantage.