I finally completed working through all the city name material including additional online research, to define city name changes and translations for most tiles on the map. The current city name manager is almost 20,000 lines long and almost three times the size of its 1.17 predecessor. It covers a ridiculous number of cities, many unlikely to ever be founded or ever be triggered in typical gameplay, but they are covered nonetheless. It is also way more detailed about giving cities different names throughout history, and changing the city that occupies a given tile based on a number of factors.
The only thing that is missing is to actually implement the logic to use all these city names. Like I explained before, the goal here is to make things more dynamic and flexible, so that it is impossible for a given civ to not have a name for a tile, and instead there is always some kind of fallback.
That is going to take a bit of additional time, but in comparison to the mountain of research I have now behind me it should be done fairly quickly, so expect city names to return to DoC 1.18 soon.