Comment # 29 on bug 939153 from Timo Sigurdsson

I'd like to chime in here. This is still an issue with Leap 15 - and more
importantly, with the release of Thunderbird 60, it's not as easy to work
around anymore, since Mozilla doesn't seam to publish the Lightning xpi
estension file anymore (or at least not in an easy to find location).

So, I had to download a release tarball of Thunderbird 60 and extract the
localized extension package from there. This is certainly anything but
user-friendly.

What strikes me, though, is the fact that I can see the official Thunderbird
packages do seem to contain localization files for the Lightning Calender in:
/usr/lib64/thunderbird/extensions/langpack-de@thunderbird.mozilla.org
(my locale is 'de')

But how do I get Lightning to actually make use of these translations?