Comment # 14 on bug 939153 from Wolfgang Rosenauer

If you pull the Thunderbird spec file you'll find the logic how the core
language packs are created.
If you find a way to use a similar process for Lightning that would help quite
a lot. I'm pretty sure there is one somehow because I expect the addon to be
built also somehow for the different locales. I just didn't have time to
experiment much with it (and probably don't have in the near future). Probably
the Thunderbird community on IRC also can give some hints how this could be
implemented.