There's a super-famous example of this very thing that linguists often cite as a clue to the divergence of languages from a common root. I've forgotten the specifics, but it comes down to two kings/war-leaders/chieftains taking an oath of friendship. One of the big dudes spoke French and the other German. So the French speaker delivered his oath in German so the German-speaking troops could hear and understand him, and the German-speaking dude dutifully followed up by repeating HIS oath in French so the French-speaking troops would know what he was promising. I was like, cool, that's neat, but the significance of this is it's the first recorded instance of French and German having diverged sufficiently from their common predecessor language as to be unintelligible to someone who didn't speak French/German.

Finding translators has been a real challenge in international relations for as long as there have BEEN international relations. The problem is that there's not a huge amount of material in the historic record as to how this was handled.

We know that Sacagawea was enough of an expert in Native Sign Language (as it existed at the time) that she was able to teach a lot of it to the Lewis & Clark party.

The pre-Renaissance reclamation of ancient Greek-language texts on natural science, literature, philosophy, art, mathematics, engineering, and astronomy relied on European monks finding translators who spoke Greek, Latin, and Arabic, and who were also scholarly enough to be able to explain the contents to the monks doing the transcribing. Legend has it this is how we got the symbol for "zero"; the monk was puzzled by the concept, so the translator obligingly recommended that he just draw a little hole in the middle of the equation.

Too, there's the example of La Malinche (a title, not her name, which has been lost) making great use of her multilingual skills to help Cortez destroy the Aztecs.

This particular story isn't told too often, but in the aftermath of the Second World War, displaced persons all over Europe took to the roads to try to walk home. As the roads got larger, the displaced found themselves sharing with the victorious military. At select crossroads, the Allies stationed multilingual Europeans who had survived the mayhem to talk to the displaced people, getting their names, home locations, and stories to help with what must have been a world-class traffic jam.

I guess, if contemporary civilization collapses, anyone who is multilingual is gonna be very, very prized.