If English communication is actually important for the job, then yes, people who can't adequately communicate in English can and should be discriminated against. And yes, people who can't adequately communicate in English tend to be born outside of English-speaking countries.
Requiring strong written English to carry boxes could be considered unfair. But for a job that involves written communication?
The problem identified by the document I saw was the vagueness of this description and also its history in discrimination. It was suggested that very specific terms be used such as "ability to write detailed and understandable reports" if that is a job requirement.
Requiring strong written English to carry boxes could be considered unfair. But for a job that involves written communication?