I thought about that, but the way the game randomly scatters City States around the map, there would be a vanishingly small chance of any IRL 'sister cities' being anywhere near each other. I think a better mechanic would be to have similar or maybe complimentary City States in some kind of proximity to each other have a chance of forming an alliance. The distance requirements could change as communications technology changes in the game.
For examples, two or more Military City States might form a Military Alliance, their combined military forces working together.
Two or more Commercial City States would be likely to form a Trade/Commercial Alliance, Religious City States might form a Holy League, etc. The actual names of the City States are less material than the type and location, which may also be easier to program in the game.