I think that there is a bug in the translation of the file menu.xml.ca in xfdesktop that don't allow a correct system menu generation (for example under the xfce menu applet) when you use a catalan language session.

The bug is in this string:
<include type="System" style="simple" unique="true" />

It should be:
<include type="system" style="simple" unique="true" />

Changing it (System by system) in my ubuntu machine solves the issue, but i can't confirm this on a debian machine or elsewhere.