civilization-5civilization-5-gods-and-kings
I've found a tile which seems to contain Porcelain:
I'm not quite sure how it happened; it seems like a city-state used to be on that tile, but it was somehow removed (I thought cities which are city-states can never be razed). In any case, Is there any way I can add this Porcelain to my luxury resources?
Although it's in my territory I don't seem to have it currently, and the tile doesn't list any improvement it needs to connect it.
If the one remaining civ has 3 city-states that they have conquered, you can liberate them to get your 3 votes. Otherwise you can't get a Diplomatic victory after you undiplomatically crushed all those city-states. =)
I highly recommend the "Luxury Resource Display" mod. It's one of the higher-ranked mods at the moment, for good reason - it makes you permanently just a mouse-hover away from seeing a detailed list of how many luxury resources you currently have of each kind, including how many are traded.
Just search for it in the in-game mod hub, it's easily found, but it seems to also be downloadable from here (I recommend the in-game method, though).
Best Answer
That same topic is covered on CivFanatics here. The conclusions they came to are:
It is likely this will be patched at some point so that the resource does not automatically appear under the city when it is conquered.