For example when I edit the entry for Celia, I can’t select “Deva” for the “Born in:” field. The city doesn’t exist in the list of cities. If I write “Deva” and then push “Enter edit”, nothing happens. My edit doesn’t appear in the history of edits.
There is only a limited list of cities that can be chosen for that field?
Is there any documentation for that decision?
There’s no decision as such: ask for the city and it will be added. It’s just we stopped adding everything automatically at some point because there were some issues 
I’ve made a request - Loading...
Got a link to those issues? I’m just curious, so only if it’s really easy to find it.
And how about automatically adding all the locations having an entry at WikiData? I’m not suggesting it, this is just curiosity.
That was what we used to do Wikidata coverage is super deep in some places and not deep enough in others (which is how we ended with a million of tiny villages in the US but without many relatively big cities outside Europe). It also had duplicates sometimes because a village had been added automatically from say the English wiki and the Cebuano wiki (which creates articles automatically from GeoNames info) and they weren’t linked. This has probably improved by now, a few years later, and at some point we should look into updating the bot code and adding things automatically again.
What I do, when a birth city isn’t available…
I select the next step up the chain.
For example -
42nd street
is on The Upper West Side
in Manhattan
which is a section of New York City
which is part of New York state
part of the USA
If I can’t find 42nd Street, I check for The Upper West Side. If no result, then I look for Manhattan. If Manhattan isn’t available, I look for New York City. And so on, and so forth.
.
**On a side note.
Was I born in a city (because that is where the hospital was), or was I born in the small town (without a hospital) where I “lived” on day one?
Selecting the closest option (the region rather than the country for example) is also what I generally would suggest - while still adding a request anyway
That’s something I’ve wondered about as well - if we count the hospital almost nobody is born in villages in Europe (and I guess the US) anymore. I think Wikidata for example do specify to add the hospital if known rather than a city, so I guess they think that’s better.
In France, it is the area where you are born that counts on ID, not the area of your parents’ house.
I think it must be the case everywhere, because it’s the easiest to determine without discussion.
I mean, I know people who were born while the parents were traveling. They were born in the travel city.
But, when it is a simple matter of a 5 mile trip from the suburbs to the “birthing center”, which may not even be in a city but, rather, in another suburb…
You can think of many examples including I know someone who was born on a boat, on international waters, no countries.
Except in this case where we may currently lack the international seas or, better, ocean name(s) area in MB, the birth place is the birth place, it is not anything else, there is no ambiguity, IMO.
A suburb is also a town, it can have its area, our we take the parent area.
Where applicable, it’s “whatever their passport/id says”.
My birthplace is Bonheiden, a small town on the outskirts of my hometown. Yes, that is only because the hospital was there; but I don’t see how that matters, as it’s also what is on my birth certificate.