Saudi Arabia
The official language of Saudi Arabia is Arabic. The three main regional variants spoken by Saudis are Hejazi Arabic (about 6 million speakers), Najdi Arabic (about 8 million speakers), and Gulf Arabic (about 0.2 million speakers). Saudi Sign Language is the principal language of the deaf community. The large expatriate communities also speak their own languages, the most numerous of which are Tagalog (700,000), Rohingya (400,000), Urdu (380,000), Egyptian Arabic (300,000), and Indonesian (250,000).
Arabic
Even during Muhammad's lifetime, there were dialects of spoken Arabic. Muhammad spoke in the dialect of Mecca, in the western Arabian peninsula, and it was in this dialect that the Quran was written down. However, the dialects of the eastern Arabian peninsula were considered the most prestigious at the time, so the language of the Quran was ultimately converted to follow the eastern phonology. It is this phonology that underlies the modern pronunciation of Classical Arabic. The phonological differences between these two dialects account for some of the complexities of Arabic writing, most notably the writing of the glottal stop or "hamzah" (which was preserved in the eastern dialects but lost in western speech) and the use of ' (representing a sound preserved in the western dialects but merged with ' in eastern speech).