'Arabic', the language of arab people, is the national language of the UAE. But UAE is fairly known to the world outside for its multilingualism. "Everything is in English", that's the USP which makes Dubai an inviting place for people from around the planet. The land was under British control until 1971, thus adopted English as its primary lingua franca. Every sign boards here is in both English and Arabic.
Besides English and Arabic, people widely speak Urdu and Hindi. Life gets easy if one knows one or two of these languages here in UAE. In fact, most of the labour class workers thrive by speaking their own mother tongue like Malayalam, Tagalog, Sinhala, Tamil, Bangla etc. They manage to make a living with little understanding of English, Hindi or Arabic along with their native language.
While applying to white collar jobs knowledge of English is a must. Knowing English makes it even easy to communicate with the native Arabs here. Most Arabs have their education in UK or USA and hence speaks English fluently in Western accent.