nice. I hope we won't have to war with Javanese Brittany

Another unappreciated quirk is that all these countries would have their own little names that are anachronistic from the natives names. Like how Sri lanka was "Ceylon" and Taiwan "Formosa"

I don't know enough to come up with one for every part of the world, but in Indian English it's common to call brits "Britishers". So I reckon Britain would be called something like "Britisheristan", with its capital being "Londopur"