Because I have a number of Serbian friends, and I can actually read/write Serbian to some degree, and I use mutt as a mail client, which runs in a terminal session. I also need C/J/K characters in my terminal font, but I don't think the VT220 ever supported them, so I'm not too upset about substitutions there. It's just disconcerting when most of the Cyrillic is in VT200 font, and just an occasional character is substituted.