Hi Anthony,
the i18n module only loads .mo files it can find (or create from .po files it 
found). Reading the code it seems that in the default case it only 
searches in some places, depending on where roundup is installed.

You can see the place it searches with the following test:

python
>>> import roundup.i18n as i
>>> i.LOCALE_DIRS
['/usr/share/locale', '../../../share/locale']

Place your ..mo or .po files there or temporarily patch 
the beginning of i18n.py.

To get a German "de" translation for demo.py I did something like
added ".locale" to LOCALE_DIRS in the top of i18n.py
and then copied the .po files to the right place (roundup compiles it then).
  mkdir -p ./locale/de/LC_MESSAGES
  cp ./locale/de.po ./locale/de/LC_MESSAGES/
  python demo.py

Let me know if this solves your case.
And please also suggest a hint for improvement of the documentation.