lxsession-edit's GUI isn't showing one string translated (Window Manager:) , see http://www.zimagez.com/zimage/capturadetela-11-05-2011-072437.php
Removing the trailing space after "Window Manager:" at lxsession-edit/data/lxsession-edit.glade (diff below) solves that. See http://www.zimagez.com/zimage/capturadetela-11-05-2011-073608.php
250c250
< <property name="label" translatable="yes">Window Manager: </property>
---
> <property name="label" translatable="yes">Window Manager:</property>
This seems to be fixed now in git.
Thanks for your bug report. It's fixed in git (the string appears in the .pot file).