For example, a Moroccan Arabic user would have trouble conversing with a Tunisian Arabic user, even though both countries are in North Africa. On the other hand, a Saudi Arabic user likely wouldn't even be able to tell Moroccan Arabic from Tunisian Arabic[1], let alone understand a Moroccan or Tunisian Arabic speaker!
The further east/west you go, the more differences arise (pronunciation, vocabulary, and grammar), and the harder it becomes for Arabic users to understand one another. But it can get even more hairy: in some cases, Arabic users from the same country can face trouble understanding one another in day-to-day speech.
Given that the goal of an FSO is to understand as much of a language as possible (I assume?), learning Arabic becomes a much more difficult task. If the goal was just to learn MSA (Modern Standard Arabic), which is the formal and written form of Arabic, then I think it would fall under the same category as Hebrew. But MSA can only take you so far and won't really help you integrate with the local population.
[1] Middle Eastern TV channels (e.g., Al Jazeera) typically include on-screen captions in MSA if the speaker is using an "unintelligible" dialect such as Moroccan Arabic.