Not sure about Vietnam but Southern China is very big on fermentation, pickling, and salting and doing that to most every food: fish, vegetables, eggs, etc... I

Not sure about Vietnam but Southern China is very big on fermentation, pickling, and salting and doing that to most every food: fish, vegetables, eggs, etc... It’s quite possible it came from Rome but the basic techniques are deeply embedded in the culture. I suspect that it is the case for most cultures in that region of the world.