There are a million and one backpackers teaching English as a foreign language in Vietnam.
Give it a try, but don't expect too much.

Yes

Start by googling the following:
TEFL = Teaching English as a Foreign Language
TESL = Teaching English as a Second Language
TESOL = Teaching English to Speakers of Other Languages

Backpackers don't get real teaching jobs in VN .. they are just fooling around in run down centers

If you are serious about teaching do a CELTA in the UK ans apply to work at good schools like ILA or Apollo

A great experience I can assure you.