I've already put every interface in each culture folder of ui and repack them. I'm using -mod: and not -mod:my_mod, because I don't modify my_mod\data\ directory, but the original Data directory of RTW. Could the error come from that? I've seen that you first copy bi into your new my_mod folder and then copy Data folder of RTW in it. Is it possible that it exist a file of bi\data\ that doesn't exist in Data\ and that is needed to make sacking work ? That could explain why it works for you and not for me.

I'm going to test what happen if I create a my_mod\ folder and copy in it Data\ of RTW.