Antea wrote:If now I begin to learn a dialect (with the time that it should imply, instead of improving my fussha Arabic), that would imply that I should only be able to use it with the people of that specific country. But what happen with people from other Arabic countries. How many dialects should I learn, then? I don't know if that would be very useful for me
For me the reasoning is very simple. I like dreaming about being able to go to the country where my target language is spoken, and spend some time working there. With Turkey and Turkish, this dream came true. I don't know if it's going to happen with Arabic, but if it ever is, I'll certainly need a dialect. I doubt I'll feel comfortable enough to pass through all the routines (job interview, residence permit, work permit, renting a flat and whatever else may be needed), and eventually making good friends, if I don't speak a dialect.
So I guess the bottom line is, when choosing between learning MSA, or a dialect, or both, it all depends on your goals. If you want to be able to communicate with as many Arabs as possible, with the least learning effort, then I guess MSA is the right choice.