Obviously, I'm posting this because I really do feel that, if you're going to move to an English-speaking country, you'd better have a decent level of English. The article also makes me think of another point: Most of the immigrants who have come to Spain in the last ten years have either been from Spanish-speaking countries (Peru, Ecuador, Venezuela....) or have made a point of learning Spanish (I'm thinking especially of the Poles and Chinese.) This makes me think of what Ludwig Wittgenstein once said: The limits of my language are the limits of my world.
Trust me: Moving to another country is terrifying enough. Wherever you go, make sure that you do everything you can not to be isolated. You don't need to integrate fully into the culture, but you do yourself no favors by purposely isolating yourself from it.