@Mark ************************
NOT true. There is a reason that the 3 southernmost provinces are under martial law will the rest of the country is not. There is a reason that foreign embassies warn their citizens not to visit the 3 southernmost provinces, whereas for the rest of Thailand it's just "exercise normal safety precautions". Similarly, travel insurance will NOT cover you if you decide to visit those provinces, whereas there is coverage in the rest of the coverage. Malaysian cell (mobile) phone signals are blocked in those 3 provinces too, so roaming isn't an option there.
Chiang Rai doesn't stand out in terms of being any less safe compared to other parts of upper Thailand, though foreign governments do warn of possible land mines at the border and drug smugglers but chances are, as long as you don't try to cross the border illegally and stick to well traveled routes, you'll have absolutely zero issues. I've been up to the Golden Triangle region many many times and was just there last month. I felt extremely safe. As safe as anywhere else in Thailand (except for areas east of Hat Yai).
Singaporeans generally don't speak Malay, unless they're of Malay ethnicity.
If you can find Malay speakers so far north (Prachuab), great. I applaud that. Its a bit surprising to me (unless these people are ethnic Malay Muslims from southern Thailand) but anything is possible. Seek and you shall find.
In Kawthoung, Myanmar, the surrounding villages all have Malay names and some of the locals speak a dialect that mixes Burmese, Thai and Malay.