Disclaimer: I know stuff all about Tiếng Việt, but it seemed really hard to learn how to hear and say the sounds when I tried for a few days with private lessons. Using so many diacritics modifies the Latin alphabet so much that it becomes something else...
It would be interesting to compare Khmer script with Vietnamese.
The Khmer alphabet seems to have 33 consonant letters, 15 vowels, 16 "dependent vowels" (which look to attach like an accent to a consonant), and 12 diacritics.
Since I don't have any knowledge of either language, I don't know if this is better.
Thanks! Since there are already many different languages using latin script I'm not surprised that this very heavily annotated version too differs. (I'm Hungarian, so maybe that's why I prefer explicit markings for pronunciation.)
Aa Ăă Ââ Ee Êê Ii Oo Ôô Ơơ Uu Ưư Yy
On each of which you can add 5 different tone marks: https://vietnamesetypography.com/alphabet/
Plus there are diphthongs and triphthongs (look at the zero coda and off glide coda columns): https://en.wikipedia.org/wiki/Vietnamese_phonology#ref_Notes
Disclaimer: I know stuff all about Tiếng Việt, but it seemed really hard to learn how to hear and say the sounds when I tried for a few days with private lessons. Using so many diacritics modifies the Latin alphabet so much that it becomes something else...