1) This case will not have adverse effect on Visa which is already granted to you. So you can travel to Vietnam.
2) I would not suggest you to go for confession as this will be a record for lifetime that you were convicted in that case even if it is only a fine.
3) No court doesn't always favour victim
4) Burden of proof always be on the prosecution to prove their case and prove that accused committed the offence for which he is facing trail.