Many years ago, when there was a lot of factory work in the US, non-English-speaking immigrants were capable to perform many jobs without having to learn the language. Then, communities of different nationalities were formed, providing all kind of services, food stores, etc.
Look what happens in Miami, for example, there's no need to speak English to be successful, on the other hand, people speaking only English may be at a disadvantage.
Only the next generation brings the benefits of a bilingual society.