Question: How do you write ''Cambodia'' in Vietnamese?
The Vietnamese use many terms to call Cambodia and the Cambodian
(1). Nước Campuchia (Cambodia) and Người Campuchia (This term is used quite popularly at the present)
(2). Nước Cam Bốt (Cambodia) and Người Cam Bốt (Cambodian)
(3). Nước Cao Miên (Cambodia) and Người Cao Miên (Cambodia)
(4). Nước Nam Vang (Cambodia) and Ngươi Nam Vang (Cambodian)
(5). Cao Man (Cambodia) and Người Cao Man (Cambodian) (rarely and used in the Vietnamese old language) (Man means Barbarians/wild and uncivilized people similar to the term “Youn” that the Cambodians use for the Vietnamese ethnic)
(6). Nước Chân Lạp (Similar to Chenla, Cambodia) and Người Chân Lạp (Cambodia) (rarely and used in the past).
(7). Nước Khmer (Cambodia) and Người Khmer (Cambodian)
(8). Nước Khơ-Me (Cambodia) and Người Khơ-me (Cambodian)
(9). Cambodia and Cambodian (Used according to the English language for English learners in Vietnam).
P/s: I write answers based upon the gist and requirement of the question. Readers are requested to read it with neutrality and rational approach. I throughout this answer has no intention of showing any disrespect towards any group of people or country.