I just spent a week in Morocco, a 3,000 USD per year GDP per cap country. In Marrakech, the modal service worker (so, we're talking about a guy who sells one dollar meat pitas, or leather goods, or whatever in a small store) speaks fluent Arabic, passable English and French, and probably at least some Amazigh. I got catcalled in German, Spanish, and Hebrew as well, just walking around shopping areas. This is a country where it's not unusual for someone to have a grade 5-8 education. I was in a Berber village where the modal young adult leaves school around age 10 to take part in agricultural activity; the village I was in got electricity around 15 years ago and is currently working on its first paved road. Everyone had conversational English, and fluent Arabic, native Amazigh -- this is probably an area where the GDP per cap is below 1,000 USD. Additionally, Moroccan Arabic is pretty strange compared to, say, standard Egyptian and so being a fluent Arabic speaker likely entails a bit more work. A friend of mine is currently in Nairobi on research (2,000 USD GDP per capita) and universally people speak fluent Swahili and English; most also speak various local languages.

In California, my social circle is mostly PhDs. These are phenomenally smart people. You go to a JPL party and the average IQ has to be 2 or 3 standard deviations above the mean. There are a lot of rooms where I'm by far the dumbest person. But most people I know are either unilingual or bilingual. Even in Southern California, a majority of people have sub-conversational levels of Spanish. I know very few people who are conversationally trilingual. Where I grew up in Canada, E/F bilingualism was somewhat common but very, very, very few people spoke a third language and most people had halting French. I'm in Ireland right now and native-born Irish speak English and a culpa focal of Irish, and that's about it.

What this says to me is that it's pretty unlikely that a country's tendency towards multilingualism is meaningfully correlated with education or economic status. And while I know the idea of measuring "intelligence" is completely fraught, I can at least say it seems unlikely that a random sample of people in one place are as intelligent as JPL people.

All this to say that in all three of the anglosphere countries I've lived in, people seem to have a mental block on the idea that a second language is essential, or that a third or fourth language are even feasible. Someone who fluently speaks four languages is considered a polyglot, a freakshow, some kind of Beautiful Mind. But then you go to Netherlands or Switzerland or Morocco and it's normal. And the reason for this isn't obvious to me: it doesn't seem to relate to income, education, it doesn't seem to obviously correlate with intelligence. It seems to just reflect some kind of cultural premium placed on language acquisition. I'd love to read more about why this is.