So I’ve seen a comment about learning Spanish making you get a little grip on Portugeese and Italian, my own language helps understand our neighbors.
I wonder, how to abuse that system for the most efficient pick of 3 or 4 languages to rule them all? Let the bar be just reading, text as simple as social media posts.
Again, not people (or we can just put this link, but languages treated as autonomous entities by science.
This should fit your need, at least for Romance languages
https://en.m.wikipedia.org/wiki/Interlingua