login only offers japanese environment

After upgrading from precise to trusty lightdm only offers to log in to a Japanese environment now (lightdm login screen, the pulldown only has "ja" on offer). I looked around but could not spot why this would be.

$ sudo rgrep -i ja_JP /etc/
Binary file /etc/.git/index matches
/etc/scim/config:/Hotkeys/FrontEnd/Trigger/ja_JP = Zenkaku_Hankaku,Alt+grave,Control+space
/etc/.etckeeper:maybe chmod 0755 './X11/ja_JP.UTF-8'
/etc/.etckeeper:maybe chmod 0755 './X11/ja_JP.UTF-8/app-defaults'
/etc/.etckeeper:maybe chmod 0644 './X11/ja_JP.UTF-8/app-defaults/TiMidity'
/etc/.etckeeper:maybe chmod 0755 './X11/ja_JP.eucJP'
/etc/.etckeeper:maybe chmod 0755 './X11/ja_JP.eucJP/app-defaults'
/etc/.etckeeper:maybe chmod 0644 './X11/ja_JP.eucJP/app-defaults/TiMidity'
/etc/locale.alias:japanese ja_JP.eucJP
/etc/locale.alias:japanese.euc ja_JP.eucJP
/etc/locale.alias:ja_JP ja_JP.eucJP
/etc/locale.alias:ja_JP.ujis ja_JP.eucJP
/etc/locale.alias:japanese.sjis ja_JP.SJIS
/etc/wwwoffle/namazu/namazurc:## Lang: Set the locale code such as `ja_JP.eucJP', `ja_JP.SJIS',
/etc/X11/xinit/xinput.d/default:# Japanese ja_JP* kinput2 "@im=kinput2" Shift-Space

$ ll /etc/X11/
total 92
lrwxrwxrwx 1 root root 13 Mar 2 2010 X -> /usr/bin/Xorg
-rwxr-xr-x 1 root root 709 Apr 1 2010 Xreset
drwxr-xr-x 2 root root 4096 Mar 22 20:57 Xreset.d
drwxr-xr-x 2 root root 4096 Mar 22 20:57 Xresources
-rwxr-xr-x 1 root root 3730 Feb 19 2010 Xsession
drwxr-xr-x 2 root root 4096 Mar 23 14:07 Xsession.d
-rw-r--r-- 1 root root 265 Feb 19 2010 Xsession.options
-rw------- 1 root root 601 Mar 2 2010 Xwrapper.config
drwxr-xr-x 2 root root 4096 Mar 23 14:41 app-defaults
drwxr-xr-x 2 root root 4096 Nov 19 2012 cursors
-rw-r--r-- 1 root root 18 Dec 24 01:06 default-display-manager
drwxr-xr-x 2 root root 4096 Mar 23 14:41 fluxbox
drwxr-xr-x 7 root root 4096 Mar 3 2010 fonts
drwxr-xr-x 3 root root 4096 Mar 23 14:45 ja_JP.UTF-8
drwxr-xr-x 3 root root 4096 Mar 23 14:45 ja_JP.eucJP
lrwxrwxrwx 1 root root 14 Mar 3 2010 openbox -> ../xdg/openbox
-rw-r--r-- 1 root root 17394 Feb 19 2010 rgb.txt
drwxr-xr-x 3 root root 4096 Mar 23 01:41 xinit
drwxr-xr-x 2 root root 4096 Nov 5 23:01 xkb
-rw-r--r-- 1 root root 270 Feb 1 11:05 xorg.conf.failsafe
drwxr-xr-x 2 root root 4096 Mar 22 20:57 xsm

$ cat /etc/environment
PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games"
LC_MESSAGES="C"

I thought that maybe this behaviour is due to the ja_JP folders inside /etc/X11 and those belong to timidity.

$ dpkg -S /etc/X11/ja_JP.*
timidity: /etc/X11/ja_JP.UTF-8
timidity: /etc/X11/ja_JP.eucJP

The strange (and upsetting) thing is that this even overrides an explicit setting I have made.

$ cat ~/.environment
#LANGUAGE="en_US:en"
LANG="de_DE.UTF-8"
LC_MESSAGES="C"