Let's see if I understand that post correctly:
When played with some mods, some of which you made yourself, it crashes (sometimes? Always?) with a c++ error
When played with no mods, it gets a "not responding" error (sometimes? Always?)
I don't understand how you could add two cultures and still get the same checksum?
To clarify things for me, try this: load the game up with NO MODS AT ALL. To make sure this is the case, go to Steam-ck2-properties, and paste this into thre Set launch options button:
-skiplauncher
Now start a NEW game (do not load any save) and play anyone ... what crash do you get, if any, and under what circumstances?