Raised multilingual here (as in father spoke one, mother spoke another, living abroad and US back and forth). I don't know about the stronger social ties but I have found that thinking in a different language helps me get to sleep easier. There are times when I'm spinning around in webs in English (work, life etc) at night, and when I switch over to Spanish thoughts I fall asleep easier.

Maybe just stuff like that is enough to make a difference.

> One thing I've never seen discussed on this topic (possible I just missed it, I only read popular accounts) is whether speaking multiple languages is a proxy for higher sociability / stronger social ties.

Yes. This is exactly what you should be asking with this kind of stuff. The research is hopelessly confounded by social status traits that correlate with wealth.

And before anyone says it, the abstract claiming "adjustment for linguistic, physical, and sociopolitical exposome factors" is fine, but it's essentially impossible to control for something as pervasive as the effects of wealth, without randomization. There are also factors -- like the culture you grew up in -- that are equally difficult to control. For example, if your dataset has only X multi-lingual Americans, and 1000x multi-lingual Western Europeans, no amount of statistical massage will correct for the imbalance.

Learning German hasn't made me more sociable.

In my world, most multilingual speakers are children of immigrant families, and that transcends socio-economic boundaries. Plenty of immigrants were already wealthy before coming to the SF Bay Area, where we import highly educated, specialized workers. On the other hand, we also import physical laborers who are also generally multilingual but not in the same social class.

Some of these immigrants are very well supported with a strong social network, while others struggle with isolation.