Lost in translation, what's in a place name?

Here is another airport shot from the tarmac, this time looking to the terminal building from the back of parking stand 31 at Geneva, or as the big sign you can read there says Genève. I've always found it weird that some places have two names, surely they should just be called whatever the people live there call them? Cologne - Köln , Naples - Napoli, Florence - Firenze, I guess in some cases it's just a pronunciation thing (Barcelona - BarTHelona for example) and there's probably some places where there's a historical reason, some dispute or other going back centuries - but how long has London been there and the French name for it is Londres? If your name is Peter you'd object to French people calling you Pierre wouldn't you so why are place names lost in translation?