Now that the release is out, I would like to suggest an idea on how to handle translation of the Megapack. This has been discussed before, and one of the difficulties raised was communicating unit names in multiplayer. Part of the community was against translating the megapack at all.
On the other hand, having part of the game in English is not attractive to speakers of other languages, including translators who will definitely have more fun if they can translate everything. For example, if I reverse my translation of one of the Tutorial instructions, it currently looks like this:
First we need a worker (obraiche). To get one, left-click on the Mainteepee (a' phrìomh thipidh) and start training your worker. To do so, use the 'Produce Worker' ('Dèan obraiche') command by clicking on the worker icon.
So, how about having it as a separate language option? Users of other languages could then, if needed, switch to a common language for techtrees only in multiplayer. The option could be placed in the main options screen and be active throughout the game, or alternatively in the multiplayer lobby, active for multiplayer only.
It would also be a great help for translators if the megapack was then added to Transifex, and to help modders to get their stuff on Transifex as well.