The marchobmenu doesn’t want to work in Sparky 3.0 with different locales then English.
It happend between packages updating from RC to the final version.
In this moment I suggest to change the marchobmenu into Debian menu.
Edit file “/home/you/.config/openbox/menu.xml” and remove the line:
<menu label="Applications" id="mom-applications" execute="/usr/lib/marchobmenu/mom-daemon.py show">
and put a new one instead of the old one:
<menu id="/Debian">
Then restart Openbox.