There is no internationally-enforceable mechanism regarding how other people call something, or what alphabet can be uses to write a word. I can legally call that country between Bangladesh and Thailand "Burma" or "Myanmar", I can call Україна Ukraine, The Ukraine, or Ukrainia (the latter seems to be old-fashioned, but it's still legal). As a diplomatic matter, the US government seems to have settled on certain designations so that it uses the version "Myanmar" for official purposes although it includes "(Burma)" in popular communications (State Department travel advisories). If it wanted to, the US could call The Republic of North Macedonia by the name "Macedonia", though there would be political protests.
The EU, NATO, UN etc. can likewise set its own rules regarding names of countries. There are many additional complications in the case of countries that are not universally / widely recognized, such as Trasnistria and the Republic of Somaliland. If the president of
the Republic of Somaliland sought to address the UN, his problem would not be what people would call his country, it is that the Republic of Somaliland is not "recognized" by the UN (it has no official status), or anyone else.
The question of "sameness" of language is a prominent feature of nationalist movements. Claims are made that Flemish and Dutch are "the same" or "different", likewise Bosnian, Serbian, Croatian, Montenegrin; Dari, Farsi and Tajik. Thus there is no real chance of litigating the matter of whether Moldovan and Romanian are the "same language" and which name should be used. But if the EU parliament wants to, it could rule that the language of Moldova is to be called "Romanian", or "Moldovan".