Created a culture of my own in the First man group. Added it to common/cultures/firstman, added some dynasties and also a line in localisation. However, the culture is now showing in the game - neither in customer ruler creator, nor by adding it via console. Are there any limitations to creating new cultures in the mod? I never had any problems in vanilla with this.
EDIT: So I found out the possible reason - I have some mods which also use the same file from "cultures". However, I am not sure how this works with overwriting. There are like 4 mods which have their own "first_men" entry in "cultures", how do I find out which one overwrites all?