Sorry, I had it posted before, but deleted it because I thought this forum was empty. Basically, my problem was that with a single civ, diplomacy text works in modular (the text in modular, the diplomacy infos isn't in modular [Assets/XML/GameInfo]). I fixed it by putting all the diplomacy text in a non-modular format (Assets/XML/Text/).
I actually got the diplomacyinfos in modular, but I didn't want to take any chances and released my mod with it in standard xml format. Maybe in the future Audio will be made modular. That would really be useful, because its annoying to create a whole XML folder just for several files.