This project is abandoned due to being flawed and there being better alternatives available.
My newer system: https://github.com/aerickt/steno-dictionaries/blob/main/README.md#vietjson
This system required the user to learn a whole new layout which just isn't necessary for Vietnamese. The standard English steno layout is sufficient already. Sticking to one layout helps to speed up the learning process (assuming the user is already familiar with the layout). It took me a month to reach 30 WPM with this system, while with my newer Vietnamese theory I have been able to reach the same speed in less than a week.
Furthermore, this system also has quite a few awkward key shapes as it utilizes the asterisk quite a lot. My newer system is a fair bit better in this regard, however, I believe user202729's system to be even better. Their system also incorporates two word phrasing, while my new system doesn't. I would have learned their system, however it does not seem to be working at the moment which is why I had created a new system (see above).
Plover_Viet
A Vietnamese stenotype theory for Plover (WIP).
Disclaimer: I don't speak fluent Vietnamese. I know just enough to pronounce syllables correctly, and that's about it. This was my attempt at creating a one stroke per syllable system that's easy to learn.
Many thanks to sammdot for this beautiful graphic!
These are all the chords in a table.
Dictionaries are in plover_viet/dictionaries.
There is also a dictionary that works with the standard English layout. Download it here. To use this dictionary, simply add it to the English system, but also remap the top S key to the number key in Plover's configuration. It's not recommended to use this to learn, since the layout and raw steno is using the English system which can be confusing.
The benefit this has over installing the system plugin is that you can easily switch back and forth between Vietnamese and English since switching dictionaries is faster than switching systems (it takes a few seconds to load the dictionaries from each system). It also means that you can use regular English punctuation and modifier strokes you may have defined without having to remap them to the Vietnamese layout.
However, keep in mind this dictionary might have a few bugs from the dictionary conversion, so expect to have to add missing entries from time to time. I've been using this dictionary for about a week without any problems.