We have now landed the last two strings that we're going to do as late-l10n for 3.1rc1 - just two changes post beta 2.
That means, that we're complete and open for you to sign-in for Thunderbird 3.1 RC1. I've just opened the milestone for sign-ins. Please go to the l10n dashboard and sign-in for your locale once your locale has gone green.
We will accept sign-ins until Monday 17th May @ 23:59 PDT, which is one day later than we have previously announced.