From their supplementary table this looks like a general cognitive ability effect, although they don't seem to have included the range of measures that are typically included in general cognitive ability measures.

The short answer is that it's difficult to say from their results, and they don't explicitly test that, but it looks like it.

That would throw under the bus a lot of race-and-IQ suppositions seeing how Africans commonly speak 3 or 4 languages, sometimes more, and a large majority of white people and Asians are monolingual.

A majority of Europeans speak 2 languages, a quarter speaks 3 or more. So it isn't a white thing, it is an American thing. And it isn't because Americans are dumber than Europeans, it is just because learning new languages makes more sense for Europeans than for Americans due to those languages being smaller and foreign languages being physically closer.

Also mastering a single language is harder than learning to get by in multiple languages, as even though a majority of Europeans can speak multiple languages a majority of them are not really all that good even in their mother tongue as we can see from standardized testing. They aren't worse than Americans, but they aren't better either, they get roughly the same results.

>A majority of Europeans speak 2 languages, a quarter speaks 3 or more.

You haven't met many Europeans have you. Not all of them are Dutch, Scandinavian, urban youth or immigrants.

>a majority of them are not really all that good even in their mother tongue as we can see from standardized testing

This makes no sense. You can't be not good in your mother tongue - it's your mother tongue. Standardized testing has no say about how a language is structured, that's an absurdly prescriptivist point of view. As for foreign language ability, in real life it's not assessed by making them sit down and pass test questions, it's assessed by having them speak and write close to a native. Someone who casually uses slang, "bad forms" and occasionally makes native-sounding mistakes is more proficient at a language than someone who speaks an academic version of it and got good grades at a test.

I had a great-grandmother from rural Moldova. She spoke Vlach, Bulgarian and Russian.

Speaking three languages is not a big deal when you live in a village where everyone else speaks them.

Apologies, I'll amend my previous comment.

>You haven't met many Europeans have you. Not all of them are Dutch, Scandinavian, urban youth, immigrants or throwawaybbb's great-grand-mother.

My grandmother knew 6 languages.

> a large majority of white people and Asians are monolingual

Please edit "white people" to "American and Chinese white people"... people from smaller countries are more prone to knowing more languages :P Also, people who migrate or travel a lot. Also, since race discrimination is still a thing in the US and not only, smart people of color do their best to appear at least as smart as they really are, and knowing foreign languages probably helps a lot.

Being white and of the right nationality in a developed country simply allows you to be lazier, and you can afford to appear "dumb" in casual life, or to focus on only what you care about, hence you'd probably not bother learning any foreign languages, the ROI would be very bad for you, others will learn your native language instead... We all have limited amounts of brainpower and we try to invest it as well as we can.

Number of language spoken is largely a function of the environment and doesn't have much to do with intelligence. If you take a highly multilingual African and drop them in America, in two generations you will likely have mostly monolingual descendants.

Not confirmed by current immigrants.

https://en.wikipedia.org/wiki/African_immigration_to_the_Uni...

You'd have to link to something more specific than "African immigration to the US" to make your point.