I tired to contact former Polish translators but without luck so far.

For mail.mozilla.org we needed Polish templates in unicode, so we created https://github.com/aviarypl/mailman-l10n-pl repository and it now contains message and template files converted to UTF-8, corrections and additional translations. I'm also planing to keep it updated for 2.1 branch (right now 2.1.19rc3).

Would it be possible to use these files to update official pl localization?

Stefan Plewako