The comparison chart shows that most direct flights to Vietnam from Asian destinations allow only 20kg for total checked baggage, with the exception of Japan. All Nippon Airways and Japan Airlines allow 2 pieces of 23kg each for Japan-Vietnam route.
As for carry-on luggage, all airlines allow one free piece of between 5kg (Air France, Air China), 7kg (Cathay Pacific, Singapore Airlines, Thai Airways and Vietnam Airlines), 10kg (ANA, Asiana Airlines, Japan Airlines) and 12kg (Korean Air) in weight.
In terms of charge for excess baggage, most airlines comply with IATA rules, though some set by additional kg and some set by weight range. Refer to the table below for further information.
Unless otherwise stated, all the below baggage allowance is quoted on routes that do not involve North American destinations for economy class.