Hi Kris, Thank you for reporting bugs in Kupfer and including the complete information needed.
It seems that we introduced a feature that depends on GTK+ version 2.20. It is an isolated thing and removing it when not available is ok (if you don't care about input methods).
I have updated our master branch with a possible fix. It would be great if you could verify that you can now run Kupfer with this fix applied.
If you have git, the following succession of commands is a very quick way to run kupfer's master branch:
git clone git://git.gnome.org/kupfer
The link to the actual change is here: