I just tried following http://www.gentoo.org/doc/pl/xfce-config.xml and the package name in listing 2.1 is obsolete. There is no xfce4 package, only xfce4-meta. The English doc at http://www.gentoo.org/doc/en/xfce-config.xml is correct. You may also want to check for other possible updates in the English doc and translate them as well.
Looks like this bugs went out of my radar when reassigned due his retirement
I've marked the translation as obsolete.