Here is the full list of all 55 50 years achievements.
Complete Pioneers special game
Complete invasion of zombie chickens special game
Complete darks times special game
Complete M special game
Complete brutal force special game
Win for egyptians
Complete 25 years special game
Win for byzantines
Win for french
Win for all nations
Win for celts
Win for japanese
Win for russians
Pick Chicken devil
Win for romans
Pick The Community
Win for greeks
Get two angels
Pick Divine Intervention
Win for british
Win without using scrolls
Get three hydras
Hire 50 peasants
Get ore armor
Win for americans
Win for any nation
Clear all available dens in one game
Reach year 40
Get a unicorn
Pick Help of the forest
Reach year 25
Clear any den
Confidient win
Win for americans on hard
Win for british on hard
Win for greeks on hard
Win for russians on hard
Win for japanese on hard
Win for french on hard
Win for romans on hard
Win for celts on hard
Win for americans on very hard (without Chicken Devil help)
Win for british on very hard (without Chicken Devil help)
Win for greeks on very hard (without Chicken Devil help)
Win for russians on very hard (without Chicken Devil help)
Win for japanese on very hard (without Chicken Devil help)
Win for french on very hard (without Chicken Devil help)
Win for romans on very hard (without Chicken Devil help)
Win for celts on very hard (without Chicken Devil help)
Win for byzantines on hard
Win for byzantines on very hard (without Chicken Devil help)
Complete Plague special game
Complete Heroes special game
Win for egyptians on hard
Win for egyptians on very hard (without Chicken Devil help)