There's a very interesting article on the Johnson blog of The Economist magazine (here) about the great variety in spoken Arabic dialects. Classical Arabic is standardised, as is Modern Standard Arabic, spoken by newsreaders and the like, but the Arabic spoken in the markets of Morocco say, is incomprehensible to a person from Iraq or another Arab country.
The title of the article, "A language with too many armies and navies?" is a reference to the Yiddish-speaking linguist Max Weber's comment on the difference between a language and a dialect - "a language is a dialect with an army and a navy".
I have personal experience of the different varieties of Arabic and how it can be difficult to make oneself understood. I taught English in Libya in the 1980s and was trying to learn Arabic while I was there. There were no classes for foreigners but I had an old BBC book and I used to get my students to pronounce the words in it correctly, then I would practise speaking to them in my limited Modern Standard Arabic. They were all extremely polite and told me how well I was doing, we kept up simple conversations, and so on. Yet, whenever I said exactly the same words to the driver who took me to and from work every day, he did not have a clue what I was talking about - it was gibberish to him. The reason for this was that my students knew Modern Standard Arabic, whereas my driver did not - he operated completely in the local dialect.
I picked up a lot of words - for vegetables, for instance - from the markets, and, in fact, if I wanted to buy things at the market, I had to use the Libyan dialect. The words were nothing like the words in my BBC book though, and effectively I had to learn two languages (I ended up with just a smattering of both).
Here again is The Economist article.