convert_family_culture_and_notify_vassals_effect

convert_family_culture_and_notify_vassals_effect = {
	# Save the root character as a reference
	save_scope_as = converting_character
	# Save the old culture as a scope
	$OLD_CULTURE$ = {
		save_scope_as = old_culture
	}
	$NEW_CULTURE$ = {
		save_scope_as = new_culture
	}
	$CONVERTER$ = {
		save_scope_as = converter
	}
	# Convert root character and AI close family members
	set_culture = scope:new_culture
	if = {
		limit = {
			is_ai = yes
		}
		add_character_flag = converted_culture_this_lifetime_ai
	}
	else = {
		add_character_flag = converted_culture_this_lifetime
	}

	every_close_family_member = {
		custom = every_close_family_member_sharing_your_culture
		limit = {
			is_courtier_of = scope:converter
			# Exclude previous generations
			NOT = { is_parent_of = root }
			NOT = { is_grandparent_of = root }
			# Only non-ruler same-culture characters
			is_ruler = no
			has_culture = scope:old_culture
		}
		set_culture = scope:new_culture
		add_to_temporary_list = notified_of_culture_change
	}
	every_consort = {
		#custom = every_consort_sharing_your_culture
		limit = {
			is_ruler = no
			has_culture = scope:old_culture
			NOT = { is_in_list = notified_of_culture_change }
		}
		set_culture = scope:new_culture
		add_to_temporary_list = notified_of_culture_change
	}
	every_consort = {
		limit = {
			is_ruler = yes
			has_culture = scope:old_culture
			NOT = { is_in_list = notified_of_culture_change }
		}
		custom_description = {
			text = decide_on_local_culture_conversion
			trigger_event = {
				id = culture_conversion.0001
				days = 1
			}
		}
	}

	# Offer every same-culture vassal a chance to convert
	every_vassal_or_below = {
		custom = every_old_culture_vassal_holding_new_culture_land
		limit = {
			culture = scope:old_culture
			culture = liege.culture
			NOT = { is_in_list = notified_of_culture_change }
		}
		custom_description = {
			text = decide_on_local_culture_conversion
			trigger_event = {
				id = culture_conversion.0001
				days = 1
			}
		}
		add_to_temporary_list = notified_of_culture_change
	}

	# Notifications
	hidden_effect = {
		every_player = {
			limit = {
				OR = {
					is_consort_of = scope:converting_character
					liege ?= scope:converting_character

					AND = {
						exists = scope:converting_character.liege
						this = scope:converting_character.liege
					}
				}
				NOT = { is_in_list = notified_of_culture_change }
			}
			send_interface_message = {
				type = msg_culture_conversion
				title = converted_culture_msg_title
				custom_tooltip = converted_from_old_culture_to_new_culture_tt
				right_icon = scope:converting_character
			}
		}
	}
}

As written in game/common/scripted_effects/00_culture_effects.txt.