If there's one thing you can do now that will set you up for the next 20–30 years: it’s learning Mandarin.

The trouble is that a billion people speak Mandarin already and many of them speak very good English as well, so your own skillset as a second language learner isn't very likely to be valuable. Unfortunately learning any language is rarely a valuable market skill on its own.

Right now Mandarin speakers in Europe are in high demand for contract support, it's different when you have a translator on a site with culture matching yours then having it in contractor's country.

tell that to my wife - native Chinese speaker - unable to find job in Europe, what you say may work for someone speaking perfectly local language (other than English), but not for just English/Chinese combo without 3rd language

just language itself isn't enough

With advanced AI real time translation I don't see any need for that.

With pervasive AI agents, intrapersonal trust between humans is going to be more important than ever.

Completely real-time translation is an impossibility since languages have different sentence orders, so it will always be an awkward filter with fits and starts that erodes trust.