I'll post my own findings as an answer because it's too long for a comment.
I have to say in advance that both the families of the groom and the bride are residents of Ho Chi Minh City, so the event might be adapted to the metropolitan customs somehow.
The wedding took place in a wedding hall in Ho Chi Minh City. As a good German I came 30 minutes before the official beginning. The groom had also told me I could show up earlier, to attend some of the official photo shootings.
I wore my best formal dress. Later on I found myself a little bit ovedressed. Upon arrival the highly professional staff explained to me that it's unusual to show up early but I did not cause any difficulties anyway. The groom asked me then to be on a bunch of pictures with his and his wife's family, which must have been some privilege, because they did pose only with a few of all the 600 guests.
The gifts were to be placed into a box on a big decorated table near the entry of the hall. I was told that it is not longer necessary to use the red envelope for the gift. In fact most guests used the white envelope in which they had received their invitation to deposit their gift.
The wedding started on the spot at 18:00 and had a tight schedule with pictures, a movie about the couple and show dance on a stage among other events. There was neither space or time for the guests to dance or mingle with each others. Great diligence seemed to be spent on the distribution of the guests over the many big tables in the hall.
We were only four non-Vietnamese and sat next to some close relatives of the groom, (brother, uncle, niece IIRC), who all spoke English fluently. I guess other than most of the guests.
The meals were as orchestrated as the whole event, which ended at 9 pm on the spot. I got the explanation for that: assuming any wedding in a big town has 200 to 1,000 guests, it is rather clear that you are likely to be invited to a wedding every two weeks if you have some relatives and friends. If weddings took the time they used to take, the employers in a city might start a mutiny if 10% of their staff came to work with a hangover every day.
The couple, knowing about our European understanding of weddings, took us to a bar afterwards.
Finally it seemed to me that weddings in the capital are somehow adapted to European or American weddings in terms of clothing, decoration and location but with some very special flavours. It was a very interesting experience I didn't want to miss!