It must be frustrating for those who have learnt a new language to realise there are multiple varieties of that language, some of which are only barely mutually intelligible. It’s like being given a master key that only works perfectly in one lock. French-Canadian, for example, retains characteristics from 17th century French that you would be unlikely to hear on the streets of modern-day Paris. (Imagine an English-speaking person sounding like they were a character from a Shakespeare play!) Similarly, someone who has studied Standard Spanish might be dismayed to go to South America only to find that Rioplatense Spanish (spoken in Argentina and Uruguay) features many unfamiliar colloquialisms, as well as the different pronunciation of many words. But when it comes to a single language that varies widely from region to region, Arabic is in a league of its own.