The po files should be openly available for download here:
https://sourceforge.net/p/gretl/git/ci/master/tree/po/
(Or of course you could clone the git repo, "clone" being the git jargon.)
Either Allin would enable the permissions for the po files, or you
could
just send the
edited files to us by email and we commit and push them.
The second option seems easier to me right now :)
Thank you again,
Artur