Now that Thunderbird 3.0 has been released and has been very well received, we are looking towards our next release, Thunderbird 3.1 (codename Lanikai).
The first milestone build of Thunderbird 3.1, Thunderbird 3.1 alpha1 will be out in a few days, but will only be release in English. The reason is mostly that we haven't been able to setup an
appropriate application target for TB 3.1 on the l10n dashboard yet (the current tb31x target is outdated). The fact, that Firefox also doesn't release its first alpha in localized versions also played into that decision.
Our next scheduled release, Thunderbird 3.1 beta1 is scheduled to be released roughly one month from now. This release will be a fully localized release. I hope you will hop on board then.