What do you mean "official latin name"? Seems to me the only Latin alphabet language without diacritics is English, but then we do use them in English for certain borrowed words (façade, piñata) or fringe uses (coöperate). I wonder how these are handled in a context like the UN where multiple languages are used.
(Possibly the answer is inconsistent, but it seems like a common enough issue that there should be some standardization)
This I just don't understand. Turkish is written in a Latin script with a few diacritics (and the extra character of the i without the dot.) It's hard to call any modification of their existing script a "romanization".
As for some of your examples, eg. Россия, I don't think they use a romanization of that word like Rossija or Rossiya at the UN, I think they use English or French translations of Russian Federation.
None of those is an official name tho, they are quite insistent that's exclusively the french one:
>Therefore, in April 1986, the government declared that Côte d'Ivoire (or, more fully, République de Côte d'Ivoire) would be its formal name for the purposes of diplomatic protocol, and has since officially refused to recognize any translations from French to other languages in its international dealings.
Pobřeží slonoviny
Pantai Gading
Norsunluurannikko