I'm catalan and in my town there're a majority catalanspeakers, but, the Spanish Constitucion I have the obligation to know and understand Catalan ans Spanish because two languages are official at all Spanish.
Now, the new citizens arrived from arround the world and this actions does an explosion of differents languages: Arabien, Chinese, Spanish (Guatemala, Bolivia, Equador, Colombia, etc.), differents languages from Africa: Mali, Ivory Coast, Niger, angola, etc. But, I think it's very important that emmigratin people learns Catalan because is the reception country