Is it possible to edit the strings in english.xml?
I tried editing english.xml (act names, boss names, etc) in the language folder.
I copied the language folder to my campaign folder in the editor tree.
I packed up the level and tried it in the regular game, but the string changes didn't seem to have taken effect. All the info.xml data did though.
It's possible I don't know how to pack levels correctly though, I simply dragged the folder of the game onto LevelPacker, then copied it to the main levels folder.