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
"Colloquial Arabic" is a collective term for the spoken dialects of Arabic used throughout the Arab world, which differ radically from the literary language. The main dialectal division is between the varieties within and outside of the Arabian peninsula, followed by that between sedentary varieties and the much more conservative Bedouin varieties. All of the varieties outside of the Arabian peninsula (which include the large majority of speakers) have a large number of features in common with each other that are not found in Classical Arabic. This has led researchers to postulate the existence of a prestige koine dialect in the one or two centuries immediately following the Arab conquest, whose features eventually spread to all of the newly conquered areas. (These features are present to varying degrees inside the Arabian peninsula. Generally, the Arabian peninsula varieties have much more diversity than the non-peninsula varieties, but have been understudied.)