Comment 13 for bug 1497473

For testing i've only upgraded, then downgraded multiarch-support; and i get that error that can be the root cause:

perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
 LANGUAGE = "en_US:en",
 LC_ALL = (unset),
 LC_TIME = "fr_FR.UTF-8",
 LC_MONETARY = "fr_FR.UTF-8",
 LC_ADDRESS = "fr_FR.UTF-8",
 LC_TELEPHONE = "fr_FR.UTF-8",
 LC_NAME = "fr_FR.UTF-8",
 LC_MEASUREMENT = "fr_FR.UTF-8",
 LC_IDENTIFICATION = "fr_FR.UTF-8",
 LC_NUMERIC = "fr_FR.UTF-8",
 LC_PAPER = "fr_FR.UTF-8",
 LANG = "en_US.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
locale: Cannot set LC_ALL to default locale: No such file or directory
Gtk-WARNING **: Locale not supported by C library.
 Using the fallback 'C' locale. at /usr/lib/i386-linux-gnu/perl5/5.20/Gtk2.pm line 126, <> line 1.
Gtk-WARNING **: Locale not supported by C library.
 Using the fallback 'C' locale. at /usr/lib/i386-linux-gnu/perl5/5.20/Gtk2.pm line 126, <> line 1.
dpkg: warning: downgrading multiarch-support from 2.22-0ubuntu1 to 2.21-0ubuntu4
(Reading database ... 241242 files and directories currently installed.)
Preparing to unpack .../multiarch-support_2.21-0ubuntu4_i386.deb ...
Unpacking multiarch-support (2.21-0ubuntu4) over (2.22-0ubuntu1) ...
Setting up multiarch-support (2.21-0ubuntu4) ...