When playing this Civ in multiplayer mode I found that it's ability - Vidovdan, can be abused in order to create a infinite culture bug. When a player playing Karađorđe passes a turn and reverts that action, the bonus culture he receives ticks again, as it counts as a "turn start."
This is a video that shows it - https://youtu.be/wAYxnVFVues

I like the Leader idea, I think the ability Vidovdan is unique and a unique idea. I'm having great fun playing as this Civ, and thank you for creating it.