I see where the OP is coming from but this is the kind of mindset that could ensure you miss out on brilliant technical hires. I have a co-worker who only started learning English 15 years ago ... he speaks very good English, but every now and then he'll make written grammatical errors and spelling mistakes. Brilliant developer.

I'm a bit OCD about grammar myself and am definitely partial to people who are excellent writers and speakers of English, but I think making an allowance for non-native English speakers could

a. help increase the diversity of people and ideas in your workplace b. make sure you don't miss out otherwise fantastic hires