That's because the signs are already added to the map. Disabling EventSigns only prevents future signs being created. You could load the game, enable EventSigns, and then hide the signs (difference checkbox from turning it off), save the game, quit, reload the game. Do you still get the error? If not, it's not a sign from EventSigns but from your own sign.
In the end, there's not a lot I can do because CvWBDesc isn't designed to understand Cyrillic signs. This bug should have nothing to do with BUG itself. Did you create your own signs on the map?
Yes, that's actually fine. Python is able to understand both types. You can move all of the BUG INI files to the "BUG Mod" folder and see if it finds them. The correct path is in the list, so it should find them there.
Are those the "search paths" or "assets search paths" that you posted? They look like a mix of the two, actually. "CustomAssets" should only be used to look for assets (images, XML, etc). The second one is used only for INI files.