[javert]

Well, it's true that being a good communicator (particularly, writing papers) is a major differentiator in terms of actual grad student success. Since the job of a CS grad student is basically to write research papers.

That said, how do you judge the English proficiency of someone from India or China, without meeting them and working with them?

They make them take standardized tests that show very basic English skills, but I think you can't really judge that well in terms of doing high-quality writing and good interpersonal communication.