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. That's a known dimension that improves health and aging and I wonder if just being able or interested in speaking with a broader swath of people is what helps more than the cognitive demands of switching.

Sadly, this beneficial activity doesn’t look promising in the longterm. Real-time interpretation of foreign languages through earbuds is already available in its nascent phase, and China at least has begun cutting foreign-language programs because such AI translation is seen as the way of future. Once this tool becomes adopted enough, the learning of foreign languages is going to become a very niche hobby. It’s already a niche hobby as many developed-country Gen Z are content with traveling and working abroad with only a knowledge of English alongside their native language.