This is a patch that makes roundupdb.py and mailgw.py
translatable. This is useful if you have a tracker only
used by non english speaking people and you want to set
tracker_language to that language. That way, nosy
messages and also error messages in mailgw.py would be
in the native language of users.
.pot and .po files can then be updated with "make
template" and usual tools of gettext.

If patch is accepted, I can also provide a french
translation of those new strings.