Hi Chiyu! I'm not sure if you're still around, but if so, I had a crack at merging Extra with BUG and ran into a serious Python exception that removes the interface. I think it's due to something that Extra relies on in the base game that BUG has rewritten, so if you have any ideas, that'd be excellent. Thanks!
The thread's here: http://forums.civfanatics.com/showthread.php?t=427647
The thread's here: http://forums.civfanatics.com/showthread.php?t=427647