Some of you may have already noticed that the next Thunderbird pre-release will not be called beta1, but alpha3 (Source).
From a localizing perspective this does not much make much difference to how things were before this announcement. Everyone, who had a green dashboard as of a few hours earlier (IIRC it were 28 locales), will now be part of the alpha3 release instead of the beta1 release. Nothing will change here.
As for how this affects the overall release plan, this is still being discussed by the Thunderbird developers. I'll update you as soon as the dust clears up.