As of midnight Pacific time yesterday (roughly six and a half hours ago) we're in string freeze for the Thunderbird 3 beta1 release.
This means that any l10n strings in the mail/ and editor/ui/ directories in the comm-central repository are now frozen. Since Firefox is also in string freeze for it 3.1 beta2 release right now the strings in browser/, dom/, netwerk/, security/manager/ and toolkit/ are frozen as well. So we don't need to worry about any breakage that might come from that front.
The code freeze for our beta 1 will be on Tuesday 18th November at 23:59 Pacific time. We'll cut the release sometime after that once we've had some baking. So this means basically that your locales should be ready by that date. I'll open up a opt-in thread for you guys as soon as the code freeze is in effect.
We will be having a test day for beta 1 soon, that will be covering the new features and checking for any significant regressions. More details coming soon.
Please check the dashboard for up-to-date information on the state of your locale. We also have l10n nightly builds available at the regular location.