Here you are, in red the additional factions:
playableengland
france
hre
spain
venice
sicily
milan
scotland
byzantium
russia
moors
turks
egypt
denmark
portugal
poland
hungary
saxons
sweden
ireland
mali
hedjaz
armenia
cumans
nonplayablepapal_states
aztecs
mongols
timurids
slave
Underneath the in-game faction names in alphabetical order:
ARMENIA - The Armenian Principality
AZTECS - The Aztec Empire
BYZANTIUM - The Byzantine Empire
CUMANS - The Cuman Khanate
DENMARK - The Danish Kingdom
EGYPT - The Fatimid Caliphate
ENGLAND - The English Kingdom
FRANCE - The French Kingdom
HEDJAZ - The Abbasid Caliphate
HRE - The German Kingdom
HUNGARY - The Hungarian Kingdom
IRELAND - The Irish Kingdom
MALI - The Ghana Empire
MILAN - The Genoese Republic
MONGOLS - The Mongol Khanate
MOORS - The Almoravid Sultanate
PAPAL_STATES - The Papal States
POLAND - The Polish Kingdom
PORTUGAL - The Portuguese Kingdom
RUSSIA - The Rus' Grand Principality
SAXONS - The Georgian Kingdom
SCOTLAND - The Scottish Kingdom
SICILY - The Sicilian Kingdom
SPAIN - The Leon-Castilian Kingdom
SWEDEN - The Swedish Kingdom
TIMURIDS - The Timurid Khanate
TURKS - The Seljuk Sultanate
VENICE - The Venetian Republic