This looks like a feature request that has already been stickied at the top of "Feature Requests". https://forums.mirc.com/ubbthreads.php/topics/106741/Emoticons#Post106741

If you're just asking about unicode characters not mapped in Fixedsys, you might try googling for Fixedsys Excelsior, which seems to map more unicode symbols, and also allows a larger range of font size than just 9. Other possible fixed fonts you could try are Lucida Console or Consolas.