Like Chris said above, an IDP is not a "driver licence". It's just a standardized form of TRANSLATION of your home driver licence into multiple languages. Your driving privileges come from your underlying home driver licence, which you must keep with you at all times and be prepared to present with the IDP if you are asked for it.
Vietnamese is not one of the languages found on the IDP (the format of the IDP is universal, the same everywhere, because the format was established by the 1949 & 1968 conventions you refer to).
I suggest you contact a Vietnamese embassy in or nearby your home country and ask them for advice. Although Vietnam may not formally recognize the IDP as an acceptable translation, it is entirely possible that they would be fully satisfied with your underlying Malaysian licence - especially if you obtained a notarized translation of the details of the Malaysian licence into the Vietnamese language.
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