The lingua franca comes from the dominant culture of the time. The massive colonial empire of Britain move things from latin to English and the rise and control of the US has perpetuated English even more so. If the Anglo countries all sank into the ocean, I doubt it would be very long until Mandarin developed into the dominant language. China would be the major trading power and without the need to work with America, there would be little need to continue with English as years progress.

> I doubt it would be very long until Mandarin developed into the dominant language.

I kinda doubt that, given its writing system.

There have been various movements that have advocated for the use of pinyin as a primary writing system, for the same reason that Beijing replaced Traditional script with Simplified.

> There have been various movements that have advocated for the use of pinyin as a primary writing system, for the same reason that Beijing replaced Traditional script with Simplified.

I don't speak or read Chinese, but my understanding is there are a lot of homophones (and a culture of homophonic puns) that would make that undesirable (e.g. https://en.wikipedia.org/wiki/Homophonic_puns_in_Standard_Ch...).

There are lots of homonyms but they are disambiguated by context. Look at it this way: you don’t need the characters when you’re listening to someone speak, so why wouldn’t you be able to sound out the phrase from pinyin and understand its meaning?

> There are lots of homonyms but they are disambiguated by context.

But wouldn't that lose something? My understanding is a lot of the puns specifically rely on the characters to force a different reading than the context would imply (or to evade censorship by having many ways to write the same sounds).

Well I would still say French would be dominant over Mandarin for several reasons. Technological advantages include current nuclear collaboration on the vast coast of China. China still does not have key infrastructure to self support.

https://www.neimagazine.com/news/newschina-and-france-sign-s...

A big joint project between China and France does not constitute an argument for learning French in preference to learning Chinese.

Nor does it constitute an argument for learning Chinese, assuming both parties already know English.

The question was "if every Anglophone country sank into the sea, would people learn Mandarin Chinese, or would they learn French instead?"

You seem to be answering some other, unrelated question.