Cruiser Elite, there are plenty of Vietnamese girls or lads in Melbourne who would make ideal checkin staff. If born here, not all could speak Vietnamese but surely many could as their parents would have ensured that they were taught both Vietnamese and English. I trust that is the 'simple solution' that you have in mind. I haven't looked lately but I would imagine that all the mainland Chinese airlines (plus Cathay Pacific) departing from Australia ensure that they have Mandarin (and for HKSAR, Cantonese) speakers available. How could checkin staff ask the 'security questions' (redundant as many of we Australians who travel frequently might believe these questions to be) if they could not speak the language of the passenger? One could hand them a card with the information on it, but getting a 'yes' or 'no' would be a challenge.
By the way, VN781 is not arriving until 1205 so my suggestion above of a '1230' departure was optimistic: more likely to be at least 1310. A332 VN-A383 is the aircraft.