When apple pay is supported in Vietnam I look forward to this

As you observed, Vietnam does not yet have Apple Pay. It is not on the list Countries and regions that support Apple Pay, but check this from time to time as this situation may change.

Apple announces the addition of countries to Apple Pay and this is generally reported by news agencies.

I'm in Saigon now and have used my Apple Watch to pay at at least 3 different pay terminals, so despite Apple Pay not being supported, it appears you can still pay via the wallet.

Agree. I was in Egypt where apple pay was not supported yet. But via the contactless readers, I could still pay by apple pay using my iPhone. That's confusing but great actually.