Verify your install. In steam right click on Crusader Kings II on your library page, chose properties, local files and verify integrity of game cache. If this would be a bug everyone would be seeing it.
If the verifying doesn't work you need to full clean install following these steps. Uninstall the game, manually delete the game folder, manually delete Crusader Kings II folder in My Documents -> Paradox Interactive and reinstall the game. If you want to keep your save games then copy them out of the Crusader Kings II folder in My Documents folder before deleting it.
This might be a long shot but as I notice you using polish crest as your avatar. Are you using the polish language in the game. If you are just change it to english as the polish language version for the game was made by third party and so Paradox is not taking resposibility of updating it. I don't think the polish language version has been updated for years.