I realize in Catalonia the language issue is complicated. Catalan has to struggle to avoid being overcome by Spanish and survive. However, instead of showing some special cases we should naturally assume that Catalan is spoken in this land and do it anywhere; any foreigner speaking Catalan means they have learned it the same way they would learn English if they lived in England.
I speak Catalan because I live in Catalonia. No more reasons are needed. When a person goes to a country, not as a tourist, but to live, it is natural that they should learn the language. No one can force them to learn it but it is the way to respect the culture they are living in.
I am a Pole who speaks Catalan, but I also speak Spanish and English. It is one of the many abilities I have acquired during my life and I hope to pick up others in the future.