Divinelight answered two possible scenarios why the text won't show up.
As for the RGSS.dll goes, I'm pretty sure if you have the Legal English version of RMXP installed, you shouldn't be encountering such a problem when playing ones running on the Japanese dll. That is, unless the game you're playing happens to be Japanese- in which case your computer may not have Japanese text support.
If the problem is the game requires a font you don't have installed, usually the font file comes with the downloaded game. Look through the folder and look for it. After which you should install it in the
C://WINDOWS/Fonts folder by copying + pasting the file over.