Vietnamese only became Latin alphabet recently (100 years ago). In fact it's always completely jarring for me to see Latin or Cyrillic characters for languages like Vietnamese [1] or Turkish [2]—about as jarring as it would be to see English written in Arabic characters. So much that, if you asked me what alphabets these languages use without giving me much of a chance to think, I would probably still intuitively reply that they use something close to Chinese or Arabic, completely forgetting the whole story changed a hundred years ago.
I understand the feeling for Vietnamese which is a tonal language, and indeed has a ton of "weird" annotations on the basic characters which make the usage of the latin glyphs pointless.
But Turkish seems to fit a latin script quite well, and the previous Arabic/Persian wasn't a "native" script for a Turkic language either, I think.
Why does it make latin glyphs pointless? Isn't it better to have a closer match to the phonemes that one actually has to say than having ideoglyphs? (Which are harder to learn, because writing and speaking becomes only loosely coupled.)
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.)
The "weird" annotations are (almost) all part of regular Latin glyphs, which is unsurprising since the Portuguese who created modern written Vietnamese patterned it after Portuguese.
If weird annotations can work for slightly different phonemes in Orthographia Bohemica and for Zamenhof, I'm sure you would be able to use them for tones as well.
You can, it's how it's done, but it means someone who knows any other language using the Latin script still can't read it.
A speaker of French, Polish, German, Hungarian or Turkish can muddle through trying to pronounce another European language using the Latin script and get 95% of it but will have no idea of how to read Vietnamese.
[1] https://en.wikipedia.org/wiki/Ch%E1%BB%AF_N%C3%B4m
[2] https://en.wikipedia.org/wiki/Ottoman_Turkish_alphabet