Maybe this will be clearer as the book progresses, but the cities represent modes of perception, states of mind, emotions, paradigms, etc., so being "in" one of the cities means that you're undergoing the experiences Calvino is describing.

Diomira could be broken down into dio (god) and mira (aim, sight), so my view is that Diomira finds its physical form in godly/heavenly sights that provoke the response that Calvino's describing. The traveler actually strikes me as the melancholic one and this is influenced by their memory. They've seen so many fantastic sights that they've grown bored of anything similarly fantastic and retroactively perceive that they've always been bored by these sights. The traveler is envious of those who retain a nostalgia for when these beautiful sights, now commonplace to them, were novel.

The multicoloured lights can be expected to come on at a certain time, implying routine, and we assume that the woman surprised by the lights is either unafflicted by either shade of memory and is living in the present, or that she's experiencing it for the first time. I think that's Calvino's way of saying that memory and comparison robs us of the present: the melancholic are slave to the mundanity they paint onto the world while the nostalgic chase a high that they don't realize isn't much higher than what's right in front of them.

I'm not 100% sure, but I think that it is a shift to Kublai Khan's interior. He continually seeks connection between these cities to justify his empire's existence, but at the same time recognizes that it's unjustified, corrupt, and crumbling. Since Kublai Khan uses the first person singular, I think that his use of "we" is on one level an attempt for Khan to distance himself from his own actions and offload the responsibility onto those around him. On another level, I think that this is Calvino introducing the idea that he's not discussing ideas exclusive to royals, but rather the human experience which involves us, the readers. That though most lack physical empires, what we understand, perceive, and feel is an empire in itself that we may never understand.

I might return to this question when I finish the book.

Interesting. I could see it carrying over if you view the enjoyment of a fulfilled desire as a possession. Do you think it comes down to that translator or is there something in Serbo-Croatian that influenced the difference? The English version is very nimble and has a lot of assonance (one of my favourite aspects of the book), so maybe the Serbo-Croatian word for enjoy didn't work in that context or something?