Yeah, we have a citizenship test in Australia. Only 1.1% of applicants fail the test, which only comes in English (I'm pretty sure) and if you fail it three times, you're out. So, it's not exactly an effective social sieve. It's also tricky to define 'proficiency'. Realistically, we've probably all met people that wouldn't pass an English proficiency test who were born in English-speaking countries and don't speak another language. Being incapable of speaking or writing a language shouldn't exclude one from participating in society, which is why we don't exclude deaf/mute people, or those whose mental health prevent them from communicating effectively. Realistically, this is as much about culture as it is language.