Max is 8
You can adjust values in worlds.sql
I could not find it in "E:\Game\Steam\steamapps\common\Sid Meier's Civilization V"
I can only find worldsizes.
I changed
Update # of Max Religions (mapsize)
UPDATE Worlds
SET MaxActiveReligions = '8'
WHERE Type = 'WORLDSIZE_TINY' AND EXISTS (SELECT * FROM COMMUNITY WHERE Type='COMMUNITY_CORE_BALANCE' AND Value= 1 );
UPDATE Worlds
SET MaxActiveReligions = '8'
WHERE Type = 'WORLDSIZE_SMALL' AND EXISTS (SELECT * FROM COMMUNITY WHERE Type='COMMUNITY_CORE_BALANCE' AND Value= 1 );
UPDATE Worlds
SET MaxActiveReligions = '8'
WHERE Type = 'WORLDSIZE_STANDARD' AND EXISTS (SELECT * FROM COMMUNITY WHERE Type='COMMUNITY_CORE_BALANCE' AND Value= 1 );
UPDATE Worlds
SET MaxActiveReligions = '8'
WHERE Type = 'WORLDSIZE_LARGE' AND EXISTS (SELECT * FROM COMMUNITY WHERE Type='COMMUNITY_CORE_BALANCE' AND Value= 1 );
UPDATE Worlds
SET MaxActiveReligions = '8'
WHERE Type = 'WORLDSIZE_HUGE' AND EXISTS (SELECT * FROM COMMUNITY WHERE Type='COMMUNITY_CORE_BALANCE' AND Value= 1 );
But it still tells me 3 religions can still be founded.