Thunderbird ignoring locale after upgrade

After the latest update/upgrade¹ thunderbird no longer uses locale-de, although it is installed.

Temporary workaround is adding a symlink like:
ln -s /<email address hidden> /usr/lib/thunderbird/extensions/

¹ update info:
thunderbird 11.0.1+build1-0ubuntu0.10.04.1 -> 12.0.1+build1-0ubuntu0.10.04.1
thunderbird-locale-de 1:11.0.1+build1-0ubuntu0.10.04.1 -> 1:12.0.1+build1-0ubuntu0.10.04.1

# lsb_release -rd
Description: Ubuntu 10.04.4 LTS
Release: 10.04

# apt-cache policy thunderbird
thunderbird:
  Installed: 12.0.1+build1-0ubuntu0.10.04.1
  Candidate: 12.0.1+build1-0ubuntu0.10.04.1
  Version table:
 *** 12.0.1+build1-0ubuntu0.10.04.1 0
        500 http://de.archive.ubuntu.com/ubuntu/ lucid-updates/main Packages
        500 http://security.ubuntu.com/ubuntu/ lucid-security/main Packages
        100 /var/lib/dpkg/status
     3.0.4+nobinonly-0ubuntu4 0
        500 http://de.archive.ubuntu.com/ubuntu/ lucid/main Packages

# apt-cache policy thunderbird-locale-de
thunderbird-locale-de:
  Installed: 1:12.0.1+build1-0ubuntu0.10.04.1
  Candidate: 1:12.0.1+build1-0ubuntu0.10.04.1
  Version table:
 *** 1:12.0.1+build1-0ubuntu0.10.04.1 0
        500 http://de.archive.ubuntu.com/ubuntu/ lucid-updates/main Packages
        500 http://security.ubuntu.com/ubuntu/ lucid-security/main Packages
        100 /var/lib/dpkg/status
     1:3.0.4-0ubuntu1 0
        500 http://de.archive.ubuntu.com/ubuntu/ lucid/main Packages