Generally Vietnamese people keep a distance when speaking to someone. Although Vietnamese people do not use gestures you should keep a reasonable distance so that speakers know that you respect them and so they also feel comfortable.
The Talking Way of Vietnamese People
The Vietnamese will also not necessarily maintain constant eye contact but will have good feelings towards a person who makes eye contact. It is considered a sign that a person is honest.
Shaking hands is fine with both men and women when greeting; but it is often seen in a formal context or with a person you meet for the first time. In a casual context, Vietnamese just say “hello” or “how are you?” instead of shaking hands. Vietnamese can hug each other but only hug relatives or close friends and only when they have not seen each other for a long time. People do not kiss each other on the cheeks in public. Pointing your finger at someone’s face is very rude. Vietnamese do not use hands gestures in communication and expect the person who is talking to keep a smiling face; however, it is also expected that they express their feelings of anger or happiness rather than keeping them inside.
You should keep a medium tone of voice when speaking. A loud tone of voice means that you are showing anger. Vietnamese prefer to speak in a very indirect manner. Important questions or issues are raised indirectly. In Vietnam, a more circular route is often more appropriate. The shortest distance between two points is not always a straight line.