I found the following in cgi/translate.py

        k = linkcl.labelprop(1)

        if value:
            l.append('<option value="%s">- no selection -</option>'
                     % ','.join(['-' + v for v in value]))

        if additional:

This looks like it may be the source of the untranslated
'- no selection -' Mathias reported. I don't quite know what
this is doing, or how to mark it for translation.
I am marking it as a FIXME in the code and referencing this ticket.

I didn't find any other '- no selection -' strings in a grep though
the templates and code.

date.py has strings like yesterday, tomorrow, and '%s weeks'
surrounded by _(...) or using ngettext. So not sure what's happening
there.

Updated RELEASE.txt with better doc on generating .po files.

Closing.