I have a template with this:
{% trans \"Log out\" %}
This is translated automatically by Django to Spanish as Terminar sesión. How
The easiest way is to collect the .po file found in the django.contrib.admin locale folder and re-compiling it (you can use POEdit for doing so).
You could also override the django.contrib.admin templates by putting them in your projects templates folder (for example: yourproject/templates/admin/change_form.html) then running makemessages from the project root (although this is no longer supported for django 1.4 alpha if i'm correct)
edit: Robert Lujo's answer is the clean method