It seems absurd to try to find a "standardized" ISO country name, especially to enforce local names in English. Country names are both endonyms (for the inhabitants) and exonyms, the way certain cultures / linguistic areas refer to another country. How exactly do you transliterate Türkiye in Cyrillic or Mongolian script, where does the umlaut go? Why would you want that, instead of leaving Mongolians to use whatever traditional name they use for Turkey?

And if Turkey can demand it, why not 日本, Deutschland or الإمارات العربية المتحدة ?