The build of CDE on Slackware has only been tested on Slackware 64 bit 14.0 RC4. It may or may not work on other versions. Here are the modifications needed to get CDE built and started.
cd /usr/lib64/locale/
ln -s de_DE de_DE.ISO-8859-1
ln -s es_ES es_ES.ISO-8859-1
ln -s fr_FR fr_FR.ISO-8859-1
ln -s it_IT it_IT.ISO-8859-1
OpenMotif on Slackbuilds: http://slackbuilds.org/repository/13.37/libraries/openmotif/
Xlt on Slackbuilds: http://slackbuilds.org/repository/13.37/libraries/xlt/
Slackware doesn't have Nawk but it has Gawk. Make a symlink:
ln -s /bin/gawk /bin/nawk
chmod +x /etc/rc.d/rc.rpc
/etc/rc.d/rc.rpc start
Note: When you first run CDE and try to run an application from the front panel, it will failed with a TT error. Log out and log back in and it will run without errors.