Arabic is the official language of the Kingdom. There are numerous dialects spoken throughout the country, but the most important are Hejazi Arabic, which originated in the Hejaz around Jeddah and is the effective lingua franca, and Najdi Arabic, spoken in the Nejd around Riyadh.
Many people understand and speak some English, although much less well than in the UAE or Qatar, for example. Hindi, Urdu and Bengali are used extensively in the markets and by expatriates from the subcontinent. All major languages are spoken in the markets of Makkah. There is also a significant Tagalog-speaking minority among expatriates.
Almost all road signs are in both English and Arabic, although the vast majority of speed limit signs use only Arabic numerals.