Game is in 2035 by that time Catalonia is a country whit a flag. So no. "Catalonia is not of ilegal flag on map" - It's a game. Deal whit it.

UPDATE: It works only for synchronized group leader. Changing it to Synchronised groups or only objects dosen't change that. Will test whit trigger.
UPDATE2: Syncing whit triggers work. But it's not appearing in briefing stage only when the mission is started.