Heya Malte & the group..
I'm trying to install contacts as well, and I tried several approaches; all HEAD, 5.2.2 core + openacs-5-2-compat non-core + mail-tracker from HEAD... and they all give all kinds of different error messages; I will post exactly what I did in each case but I actually have to do it again to get those.
The other problem is there are a lot of missing localization keys. Is the translation server back? How would I go about getting translated message catalogs from it? If you want a list of keys that are missing I can get those too, but again, I would have to repeat the process of getting the stuff.