They live here. They should learn the language - just like those "ex pats" in Spain and Malta.
And how many ex-pats in Spain learn Spanish beyond rudimentary requests in shops and bars, I wonder?
People who live here are under no obligation to learn any language, of course. They require conversational English for many day to day tasks, no doubt, but anything beyond that is their choice. English people in Wales are under no obligation to learn Welsh, though the rudimentary basics would be a good start, not to mention polite. The balance is always there to be struck. I wouldn't dare suggest that an immigrant must learn perfect English before being given the chance to earn a wage.
Given the English used on the streets in every day Britain - that fused with Internet slang, that born from "Hinglish" and "Franglais", that from those born in the 1960s, that from those born in the 2000s, that used by Polish cleaners in hospital corridors, that used by mechanics on a Friday night in a provincial club, that used by Asian supermarket owners, that used by rail enthusiasts, that used by teenagers on street corners - there cannot be a single, solitary, official "English" which must be learned by "them" anyway.
We are a nation born of conquest, immigration, war, and migration, a literal mix of races on a rainy island in the Atlantic. Our language is a mix of Celtic, Arabic, even Afrikaans. We have no right, no right at all, demanding that other people must speak English, nor do we have the right to define what is correct or incorrect English.