Well, it is easy. Mandarin is a quite useful language if you are living in China, but it wouldn't help you if you are in Iceland.
Also, I've heard (don't remember where...) that not all languages are equal when conveying an idea: for example eskimos have a lot of words for snow and white. Some concepts would be very hard to express in any other language.
My point of view is clearly viased: I speak Catalan and Spanish (mother tongues) and I'm more or less fluent in English (hoping to take the CPE this june).
Also, I've heard (don't remember where...) that not all languages are equal when conveying an idea: for example eskimos have a lot of words for snow and white. Some concepts would be very hard to express in any other language.
My point of view is clearly viased: I speak Catalan and Spanish (mother tongues) and I'm more or less fluent in English (hoping to take the CPE this june).