I tried both "us,el" and "us+el" but the language steal is not able to change. Accidentally, I found out that language can change only from US to EL by pressing ctrl+alt+K . I don't know why this happens! Now, my code in the keyboard section of xorg.conf is:
Section "InputDevice"
Driver "kbd"
Identifier "Keyboard[0]"
Option "Protocol" "Standard"
Option "XkbLayout" "us,el"
Option "XkbModel" "pc104"
Option "XkbOptions" "grp:alt_shift_toggle"
Option "XkbRules" "xfree86"
EndSection
Can you see something wrong??