In my game, Fall of Bronze, the Theme "Take Care" was implemented in two ways. Firstly, you have to "Take Care" of a Nation during the Bronze Age Collapse. However, given the extremely unstable time of the Bronze Age Collapse, you have to "Take Care" with every action you take, lest you begin your downfall(this is implemented by there being a limited number of actions each "Season"/turn).
For the Extra History theme, I used the Bronze Age collapse. There are included several things like famines, earthquakes and of course the Sea People, in accordance with the Extra Credits videos on the Bronze Age collapse and that of Historia Civilis.
Unintentionally, for Extra Retro, I made it all in a depressing color(except for icons for individual provinces).
Though I did not have the time to fully implement the Extra Translation challenge, I (as nerdy as this sounds) had a Constructed Language laying around so I translated a very small amount of things to it(Three words)
As for Extra Distance, the lack of a tutorial really did distance some players from the game!