The main mailing list for translators in KDE is the mailing list called kde-i18n-doc.
You can subscribe it at its Mailman interface.
The archive is at lists.kde.org. (The archive is public.)
The direct email is
(kde-i18n-doc AT kde.org).
Even if the mailing list has "doc" in its name, it is not limited to discussions about translating documentation. (The name has historical reasons. There were two mailing lists for discussing about translations. As it soon seemed to be futile, only one was kept. The mailing list kde-i18n-doc was the more active, so it is this one that was kept.)