Alright, so lets say a group from Mars shows up tomorrow, we would naturally call them Martians, and call their home planet Mars. If they had a different name for themselves, we may switch to that. But I would imagine we would continue to call the planet Mars. Even though they have a greater claim to it.
That’s what I mean when I say who’s “right” when it comes to a name. Our language has naturally evolved to include Martians and Mars as the given names for those things. Theirs would have evolved to use different terms. Germany was Germany to those who spoke English long before the country was established and called itself Deutschland.
To take the example further, if that race had a different name for the sun, which should we use?
Languages evolve from culture while countries are political constructs. Languages will evolve according to the information available to the culture, but the goal is always communication and to be understood by the other party. Espana and Deutschland are confusing, Spain and Germany are almost universally understood by those who speak English.