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But that's unlikely. For one, English happens to have gotten there first. It is now so deeply entrenched in print, education and media that switching to anything else would entail an enormous effort.
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This is relevant because?
History has shown that just because you got there "first" doesn't mean you are going to "win".
I don't see many people writing in hieroglyphics, do you?
English is also only "deeply entrenched" in English speaking countries, and those where the economy is based on tourism.
Look at the Beijing Olympics for an example of how "entrenched" English is in China. I think everyone remembers the pictures of "500 server error" restaurant.
"Mandarin" didnt become the "default" language of China overnight. It came via conquests of smaller states and then converting them to mandarin. This is why China's official language is mandarin, but you often find people who speak another dialect as well.
Case in point, my wife is a native mandarin speaker. She comes from a province that only speaks mandarin. Her cousin speaks mandarin and fuzhou, when he speaks mandarin she understands what he says and this is not true when he speaks fuzhou.
Whatever the "default" language of the future is, it will be done over time and by having a lot of people speaking two (or more) languages.