The program does not have support for utf-8 encoding in chat. Test it with this alphabet:A, Á, B, C, Cs, D, Dz, Dzs, E, É, F, G, Gy, H, I, Í, J, K, L, Ly, M, N, Ny, O, Ó, Ö, Ő, P, Q, R, S, Sz, T, Ty, U, Ú, Ü, Ű, V, W, X, Y, Z, Zs

its not even hungarian, i have the same problem with german üöäÜÖÄß - it seems like that messages from mIRC users have the wrong encoding, but other irc clients (or old versions of mIRC) are not affected by this problem.
i dont think thats a bug of mIRC, i tested everything out and the more i look and test, the more i think it must be a bug in craftirc3.

Its better on MC 1.4+ versions.

so i found out, its all irc clients using unicode which have this problem. the "old mirc" versions use latin-1 encoding. mirc 7.x uses uncicode.
(bukkit #2717 / mc 1.5.1)

mirc is 90ties :) anyway you can try to chang charset in view-fonts-utf8