Menues gone after Ubuntu update

Today Ubuntu (16.04) installed some security-critical updates and afterwards prompted me for a restart. After the restart several programs had lost their menus (which are normally shown instead of the window title when I move the mouse into the title bar. Under these programs are nautilus, gnome-terminal and LibreOffice but not Firefox and Thunderbird (which, afaIu, build their own menues).

I started a "compiz --replace" in a terminal, and it showed the following messages (menues were still gone):

    ERROR 2016-05-06 17:12:02 unity.glib.dbus.server GLibDBusServer.cpp:538 DBus name lost 'org.gnome.Shell'
    ERROR 2016-05-06 17:12:02 unity.glib.dbus.server GLibDBusServer.cpp:538 DBus name lost 'com.canonical.Unity'
    WARN 2016-05-06 17:12:02 unity.key.gnome.grabber GnomeKeyGrabber.cpp:94 Trying to grab a disabled action, we skip it
    WARN 2016-05-06 17:12:02 unity.key.gnome.grabber GnomeKeyGrabber.cpp:94 Trying to grab a disabled action, we skip it
    WARN 2016-05-06 17:12:02 unity.key.gnome.grabber GnomeKeyGrabber.cpp:94 Trying to grab a disabled action, we skip it
    WARN 2016-05-06 17:12:02 unity.key.gnome.grabber GnomeKeyGrabber.cpp:94 Trying to grab a disabled action, we skip it
    WARN 2016-05-06 17:12:02 unity.key.gnome.grabber GnomeKeyGrabber.cpp:94 Trying to grab a disabled action, we skip it
    WARN 2016-05-06 17:12:02 unity.key.gnome.grabber GnomeKeyGrabber.cpp:94 Trying to grab a disabled action, we skip it
    WARN 2016-05-06 17:12:02 unity.key.gnome.grabber GnomeKeyGrabber.cpp:94 Trying to grab a disabled action, we skip it
    WARN 2016-05-06 17:12:02 unity.key.gnome.grabber GnomeKeyGrabber.cpp:94 Trying to grab a disabled action, we skip it
    WARN 2016-05-06 17:12:02 unity.key.gnome.grabber GnomeKeyGrabber.cpp:94 Trying to grab a disabled action, we skip it
    WARN 2016-05-06 17:12:02 unity.key.gnome.grabber GnomeKeyGrabber.cpp:94 Trying to grab a disabled action, we skip it
    X does not support your locale

Could that be related to the problem? I have been using LANG=eo.utf8 for several years.

"uname -a" says "Linux xxxx 4.4.0.21.generic #37-Ubuntu SMP Mon Apr 18 18:33:37 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux".

What can I do to get my menues back? Any help appreciated.