In Thailand, probably different in Urban (and heavy tourist places) and rural locations?
My experience was from Bangkok, and it wasn't good on the streets for folks with mental health issues. Yes, some support from locals, but also a lot of abuse. The local temples obviously do add a social net of some type, but some temples seem to have limitations on how much support they can/will give out to certain folks in their community (?) - again, just my limited experience. The temples are a good social safety net though - imagine how little support some folks would have without them.
Pure mental health issues, not drug or alcohol dependent, seem far higher to me in Thailand than elsewhere; just anecdotal. It would be interesting to see statistics. In Korea, mental health issues are still taboo to the older generation, so a lot is hidden; it's getting better with good doctors and empathy from the younger generations.