Why is that though? Isn't it the same as in Arabic? I thought French is the same everywhere.
Yeah I have noticed what you're talking about but I don't think it's that hard to learn. Egyptian Arabic is the most well-known Arabic.
Btw, when you're talking about Standard Arabic, you do mean fusha?
Actually, most Arabic speakers have trouble understanding and speaking fusha (there have been many Arab educators and linguists who have talked about the issue and ways to solve it). Peculiarly, all the Arabic speakers I have met who don't understand fusha also understand dialects outside their own (although geography does play a factor).
Yes, I meant fusha, or some approximation thereof (the modern, somewhat simplified variety of it). A complete knowledge of "Arabic" requires mastering that as well, since it is used widely in formal context (TV news) and almost exclusively in formal writing (most novels, newspapers etc.). While many Arab people do not speak it fluently, some education in it is very widespread and this helps smoothing out differences among dialects and offering a degree of common ground (alongside, as you said, the widespread use of Egyptian Arabic in movies and other media making it well known). Most non-Arabic students of Arabic start out with fusha and then learn some dialect (if they ever do; I specialized on Classical Arabic and my ability to use spoken registers is quite limited).
Also, the grammatical pecularities I listed for Cairene Arabic as opposed to fusha are shared by the vast majority of other spoken Arabic varieties, so that the basic structure of grammar is, in many respects, closer between say Egyptian and Moroccan than between fusha and either vernacular (there of course exceptions though). This is another level helping a degree of mutual intelligibility
given exposure. For a comparison, Italian and Spanish are certainly seen as different languages and, while quite close, are not actually mutually intelligible; but, given adequante exposure, Italians usually manage to reach a level of Spanish sufficient for most basic needs, though not necessarily an entirely correct one, in a few weeks or months (some complementary study hastens the process). The reverse is also mostly true. The two systems are so similar that acquisition is relatively easy (though not complete in this way alone). Some Arabic dialects are more different grammatically than this, but then there are other commonalities easing the process. Also, while French is a Romance language like Italian and Spanish, the same process does not apply there. My personal experience is probably not to be generalized, but I had to learn French by studying it (and studying it
hard, though it was not particularly difficult) for years in class. I have a good mastery of Spanish that I acquired with a bit of study (by myself) some reading practice, and exposure (both in Spain and with Spanish speakers in Italy).