The Economist writes that the general perception that Arabic is a single language is somewhat mistaken:

• Arabic spread across the world 1,400 years ago, and since then it has become increasingly fragmented through regional variations.
• It is now more like Latin in medieval Europe where classical Latin was what people wrote and studied, but those who spoke were really speaking French, Spanish, and Portuguese.
• Similarly a standard form of Arabic is mostly used in political speeches, the news, and in writing – but this is not the version of Arabic that is spoken at home.
• For example an urban Algerian and an urban Jordanian wouldn’t be able to speak to each other if they spoke naturally – but they could communicate by reverting to formal standard Arabic.
• This also means that those looking to learn the language have to learn how to read and write one version of it – and then learn to speak an entirely different version that only a subset of Arabic-speakers will understand

See a demonstration of how different the various strains of Arabic are, why this is a problem of too many navies, and more over here.

Source: The Economist