xkeyboard-config version is 2.38 on Slackel repositories. While current version is 2.40 on Slackware current. This is because upgrading xkeyboard-config could not change keyboard to Greek with fbxkb. Finally i found that in latest xorg "us,el" is not working and have to use "us,gr" instead. So i edited the keytable file in salixtools replacing el with gr and also ~/.polytonic script to change keyboard to Greek monotonic/polytonic, replacing also el with gr in setxkbmap command, and recompiled the user-settings-slackel-openbox package.
So latest version 2.40 of keyboard-config is used now.
Maybe have to run the keyboardsetup to set again keyboard to "us,gr"