I use xmodmap to change my keyboard layout to romanian but I also need to change the character encodings to iso8859-2 for romanian characters to be properly displayed and I don't know how to do this.
Does anybody have any idea?

De ce nu folosesti Gnome Keyboard Preferences?

Sau nu se poate in Slackware?

Five years later I found out how to setup the keyboard using xorg.conf which is better than anything else so I'm posting this here in case anybody else wants to solve some similar problem:

I modified these lines:

Section "InputDevice"
Identifier "VMware Keyboard"
Driver "kbd"
# Option "Protocol" "Xqueue"
# Option "AutoRepeat" "500 5"
# Option "Xleds" "1 2 3"
# Option "XkbDisable"

Option "XkbRules" "xorg"
Option "XkbModel" "pc105"
Option "XkbLayout" "us,ro"
Option "XkbVariant" "basic,winkeys"
Option "XkbOptions" "grp:ctrl_shift_toggle"
EndSection

The places you should watch closely are XkbLayout and XkbVariant. You can find the settings for these inside /etc/X11/xkb/rules/xorg or xfree86 depending on what XkbRules you choose.

You can also use setxkbmap to setup these settings at run time (no need to reboot X)