romanised characters are not roman characters though. Omitting the tones the words become unintelligible, as far as I can tell.

What grandparente says regarding using hangul to express non-korean makes no sense to me.

Sure, I can mostly get korean pronounce right using hungarian spelling, but it fails miserably the other way around.

If a language is homophonic to hangul than of course it can be used for that, but the same is true of latin or most anything else.

Yes, you are right, nowadays Vietnamese did not use Chu Nom anymore. I think the main reason is because of its complexity.