Hi. Unfortunately, RPGMaker 2000 doesn't support vietnamese font by default, but there's a solution for that. Check out this article: https://rpgmaker.net/tutorials/2503/
Basically, you have to create your own font for this (but first check out, that there's no vietnamese font patch for RM2000 already, so your efforts won't be in vain).
I never tried to change the RM2000 fonts so I have zero experience in that regards, but as far as I know, it's the only option.
Thank you, thanks to your idea I was able to do this 