Here, I like to share my two Eastern European civilization designs: Armenian and Lithuanian.
Civ Ability: High Hayastan
International Trade Route doesn't provide normal yields. Instead, it provides 2 Gold and Faith per turn per the number of Destination city's Specialty Districts (including City Center).
Can purchase Holy Site, Shrine, and Temple by Faith.
In a city purchasing building or district by Gold or Faith, +25% Culture and 3 Loyalty per turn for the next 10 turns.
Unique Unit: Fedayi
Replaces Line Infantry. Unlocks at Nationalism, instead of Military Science.
+7 Combat Strength within 3 tiles of the Armenian border tile.
+2 Movement when starting a turn in Armenian territory.
Unique Improvement: Vank
Unlocks at Theology. Can only build on a land tile adjacent to a mountain. Cannot be adjacent to another Vank.
Provides 2 Faith per turn. If there's another Vank within 2 tiles, provides 2 Culture per turn as well. If there are 2 Vanks within 2 tiles, provides 2 Science as well.
All bonuses are increased 2 to 3 at Nationalism.
Leader Bonus (Gagik I): Glory of Ani
Receive 1 Culture per turn per the number of Destination city's Specialty Districts (including City Center) in the international Trade Route.
Units purchased by Gold or Faith receive double experience before upgrading.
Can build Khachkar unique building with Mysticism.
Leader Building (Gagik I): Khachkar
Unlocks at Mysticism. Provides 1 Loyalty, 2 Faith, and 2 Gold per turn.
Cannot be built if Monument has already been built in this city.
Agenda (Gagik I): Bagratid Dynasty
Tend to purchase military units with Gold or Faith. Likes civilizations with high Gold and Faith output. Dislikes civilizations with low Gold or Faith output.
Leader Bonus (Tiridates III): Light of Grigor
Can't obtain Great Prophet. Receive an inspiration bonus of the current era when a civilization already met found a religion.
Can "adopt" a religion when a civilization already met found a religion. When "adopting" a religion, the Armenian capital immediately converts to it and spawns 2 Missionaries of the religion. Can't "adopt" more than 1 religion.
Receive 10% Culture and Faith of the civilization found a religion Armenia believes.
+ "level of activated Religious Alliance X 10" % Faith per turn.
Agenda (Tiridates III): The First Convert
Likes civilizations believe in the same religion and with high Faith output. Dislikes civilizations following other religions or with low Faith output.
Lithuanian - Gediminas
Civ Ability: Vytis
Shrine receives 1 Relic slot. The relic slot is automatically filled when a temple is built.
Each Relic in a city reduces the cost of purchasing units or buildings with Faith by 5%. (max. 30%)
Leader Bonus: Athens of the North
Can't found a Religion. Don't receive Religious Pressure from other Religions.
Can choose the second Pantheon when obtaining the first Relic. Can choose the third Pantheon when getting the second Relic.
Can purchase Inquisitor without founding a religion. Lithuanian Inquisitor removes every religion in Lithuanian city.
Unique Unit: Leitis
Replaces Courser. Higher Combat Strength. (50 vs. 46)
No Movement penalty in Forest. +6 Combat Strength when fighting in Forest.
Unique Building: Sacred Grove
Replaces Grove. Receive 1 Relic slot.
In addition to the functions of Grove, grants 2 Faith per turn to every Preserve within 6 tiles if the city with Sacred Grove doesn't have a Majority Religion. This bonus can be stacked.
Agenda: From Sea to Sea
Focuses on building up Faith and territorial expansion. Likes civilizations that follow their lead and dislikes civilizations which is not.