Comment by kjellsbells

No. I think it's easy to underestimate what an incredible superpower native English fluency is, and the lengths that immigrants will go to ensure that their children are fluent in it. That alone stops monolingual enclaves persisting.

The net (and the UK has decades of experience in this, eg with the South Asian immigrants that arrived in the 1950s-1970s) is that while the first generation may only get to decent levels of English, their children are bilingual or monolingual in English, not monolingual in their ancestral tongue.

Occasionally you will get someone with a political axe to grind who visits an area with a lot of immigrants, doesnt hear a lot of English, and posits that there are ethnic monolingual enclaves where they cannot go. I think this is more likely to be a failure of understanding.