I took a very quick glance at the OSQA source code, and all of their urls are translated. So, you can just modify https://github.com/OSQA/osqa/blob/master/locale/en/LC_MESSAGES/django.po line 398, run django-admin compilemessages
and done.
For more info on customization, look at section D in https://github.com/OSQA/osqa/blob/master/INSTALL