Suggestion.
Gauls:
Ambigatos: Bonus in population capacity given by any CC
Vae Victis: Resources acquired from destroying and capturing buildings
Headhunting: Resources acquired from killing heroes (or champions too).
Invented the Reaper: Bonus in collecting food from farms
Montefortino: team bonus, reduced blacksmith tech cost and research time
Britons:
Sheep Age: Bonus related to livestock
Inis Mona: Druids increase attack speed of nearb