Khmer or Cambodian is the language of the Khmer people and the official language of Cambodia. With approximately 16 million speakers, it is the second most widely spoken Austroasiatic language (after Vietnamese). Khmer has been influenced considerably by Sanskrit and Pali, especially in the royal and religious registers, through Hinduism and Buddhism. The more colloquial registers have influenced, and have been influenced by, Thai, Lao, Vietnamese, and Cham, all of which, due to geographical proximity and long-term cultural contact, form a sprachbund in peninsular Southeast Asia.

It is also the earliest recorded and earliest written language of the Mon–Khmer family, predating Mon and by a significant margin Vietnamese, due to Old Khmer being the language of the historical empires of Chenla, Angkor and, presumably, their earlier predecessor state, Funan.

More Info: en.wikipedia.org