I found these in strat.txt, not sure if they're usefull:

Code:
{SMT_CAPABILITY_POPULATION_GROWTH_BONUS}		Population growth modifier
{SMT_CAPABILITY_POPULATION_LOYALTY_BONUS}		Population loyalty modifier
{SMT_CAPABILITY_POPULATION_HEALTH_BONUS}		Population health modifier
{SMT_CAPABILITY_TRADE_BASE_INCOME_BONUS}		Trade income modifier
{SMT_CAPABILITY_TRADE_LEVEL_BONUS}			Trade level modifier
{SMT_CAPABILITY_TRADE_FLEET}				Trade fleet
{SMT_CAPABILITY_TAXABLE_INCOME_BONUS}		Taxable income modifier
{SMT_CAPABILITY_MINE_RESOURCE}			Mining
{SMT_CAPABILITY_FARMING_LEVEL}			Farming
{SMT_CAPABILITY_ROAD_LEVEL}				Roads
{SMT_CAPABILITY_GATE_STRENGTH}			Gate strength
{SMT_CAPABILITY_GATE_DEFENSES}			Gate defences
{SMT_CAPABILITY_TOWER_LEVEL}				Tower defences
{SMT_CAPABILITY_ARMOUR}					Armour
{SMT_CAPABILITY_STAGE_GAMES}				Stage Games
{SMT_CAPABILITY_STAGE_RACES}				Stage races
{SMT_CAPABILITY_POPULATION_FIRE_RISK_BONUS}	Fire risk modifier
{SMT_CAPABILITY_WEAPON_SIMPLE}			Simple weapons
{SMT_CAPABILITY_WEAPON_MISSILE}			Missile weapons
{SMT_CAPABILITY_WEAPON_BLADED}			Bladed weapons
{SMT_CAPABILITY_WEAPON_SIEGE}				Siege weapons
{SMT_CAPABILITY_WEAPON_OTHER}				Special weapons
{SMT_CAPABILITY_BODYGUARD}				Bodyguard			
{SMT_CAPABILITY_RECRUITS_MORALE_BONUS}		Recruit morale modifier
{SMT_CAPABILITY_RECRUITS_EXPERIENCE_BONUS}	Recruit experience modifier
{SMT_CAPABILITY_HAPPINESS_BONUS}			Happiness modifier
{SMT_CAPABILITY_LAW_BONUS}				Law modifier
{SMT_CAPABILITY_CONSTRUCTION_COST_BONUS_MILITARY}	Military construction cost reduction
{SMT_CAPABILITY_CONSTRUCTION_COST_BONUS_RELIGIOUS}	Religious construction cost reduction
{SMT_CAPABILITY_CONSTRUCTION_COST_BONUS_DEFENSIVE}	Defensive construction cost reduction
{SMT_CAPABILITY_CONSTRUCTION_COST_BONUS_OTHER}		Civil construction cost reduction
{SMT_CAPABILITY_CONSTRUCTION_TIME_BONUS_MILITARY}	Military construction time reduction
{SMT_CAPABILITY_CONSTRUCTION_TIME_BONUS_RELIGIOUS}	Religious construction time reduction
{SMT_CAPABILITY_CONSTRUCTION_TIME_BONUS_DEFENSIVE}	Defensive construction time reduction
{SMT_CAPABILITY_CONSTRUCTION_TIME_BONUS_OTHER}		Civil construction time reduction
as for plugins, they also appaer in battle.txt in the "world" folder, which is an example of descr_strat files. the example is "plugin tax_collector senior_tax_collector" seems like a building + building level. I'm not sure if and how this is related to the plugins in export_descr_buildings though.