Different grad schools surely have different policies on this. Check the Web sites of some grad schools that you think you might be interested in.
When I was at U of Michigan (late 1970s and early '80s) there was a language requirement. I think it had to be either German, French or Russian. The idea was that you had to be able to understand scientific material in some language that was commonly used for scientific papers. I don't remember if this was a physics-department requirement, or a general graduate-school requirement.
I had taken several German courses beyond my undergraduate college's requirements, so U of M accepted that as satisfying their requirement. My roommate had also studied some German, but not enough, so he had to spend some time reviewing scientific German and then take an exam.
This may have changed since I was at U of M, of course.
