Vietnamese food stand at Thung Sri Muang Night Market. A woman of about 20 I spoke to couldn't understand Vietnamese, but this old woman did. Her Vietnamese was a bit odd, so she probably doesn't use it very often. She may even have been born in Thailand.

After the Vietnam War, there was a lot of anti-Vietnamese sentiment in Thailand because 1) Communist victories in Vietnam, Laos and Cambodia inspired Thai Communists, with Vietnam as their main backer 2) Thailand was overwhelmed by waves of Vietnamese refugees (as well as those arriving from Laos and Cambodia). Facing hostility, long-time Vietnamese residents of Thailand didn't dare to speak Vietnamese in public. Right after the Fall of Saigon, some Viets in Thailand even returned to Vietnam, a huge mistake.