When you say those characters don't work, do you mean they produce incorrect output when used with another letter (as in, typing "`e" produces "`è"), or do you mean something else?

The ˇ character and letters using that diacritic are not in the Windows-1252 character set, so you won't get exactly what you expect when you type them in.

Any characters that are not visible on the menu screen but are visible when in a game are menu font issues that I cannot solve at the moment.