Your wand would also need to erase the reason people speak (or don’t speak) the languages they do, otherwise what you said would already be true for the UK, Australia, etc.
What language do you think Germans and Spaniards use to do commerce with each other? There needs to be a common language, there’s no bandwidth to learn all languages, so due to historical and modern reasons, English prevailed.
Re Australia, Australians have highly preferential options to move to US which is not reciprocated.