A few days ago I installed KDE on Ubuntu, which added the Kubuntu boot splash. When I installed the *rest* of KDE via synaptic: on the next boot it broke GDM and my Gnome session until I did an apt-get remove followed by an apt-get install of the gdm and ubuntu-desktop packages. This is deffo one of the reasons why the distinction on BSD between /usr and /usr/local is a good thing (tm).
This after noon I clicked through one of Gnomes settings bit for languages, and thought perhaps it would have a way to merge my preferences for U.S. and ISO formatting. It asked if I wanted to install a few dozen more language packs for English and German, since I had taken the liberty of adding the German language packs. Also told it to prefer the British English and standard German languages above standard English (rather than ignored); American English being the primary. Being American, you never have to worry until you start spelling in different dialects. That added export LANGUAGE="en_US:en_GB:de:en" to the end of my .profile; which I moved to an /etc/profile.d script.
'lo and behold on reboot, the entire Gnome desktop is in German.... and despite that being very different than my limited reading vocabulary, I still can figure out what the frig I'm looking at! Just don't ask me to pronounce it properly lol.