(NOTE: DO NOT USE STEAM. There will be plenty of error's with it, even if it works. Such as files now downloading. For example if you do not have interracial marriage as a game rule then steam likely missed a file.)

If it doesn't show up in the launcher after subscribing that is probably since you have too many mods for CK2 (I think it starts having problems at 50), unsubscribe from it, then unsubscribe from some other mods, then subscribe again, it should work.

If you decide to use the Moddb version here's how to manually install mods (In case this is your first time): After it downloads extract it into the mod folder for CK2, if it doesn't show up in the launcher go into the mod folder, then the Warcraft folder if there is only a folder, and a .mod file cut and paste them both into the mod folder, then it should work.

Make sure you have these DLC's for functionality, Horse lords, Reapers due, Monks and Mystics, and Jade Dragon is recommended. You can still play the mod without them, it will just lack features.