All of that is bogus.
Here is the current research:
But a growing number of psychologists say that this mountain of evidence is actually a house of cards, built upon flimsy foundations. According to Kenneth Paap, a psychologist at San Francisco State University and the most prominent of the critics, bilingual advantages in executive function “either do not exist or are restricted to very specific and undetermined circumstances.”In some areas, bilingual education appears to be a plot to teach Mexican-Americans Spanish instead of English in schools, in order to keep them as an unassimilated worker class.
Paap started looking into bilingualism in 2009, having spent 30 years studying the psychology of language. He began by trying to replicate some seminal experiments, including a classic 2004 paper by Bialystok involving the Simon task. ...
“It was a really exciting finding and one that I thought would be easy to study with my students,” says Paap. “But we just couldn’t replicate any of the effects.” After years of struggling, he published his results in 2013: three studies, 280 local college students, four tests of mental control including the Simon task, and no sign of a bilingual advantage.“That broke the dam,” he says. “Others started submitting negative results and getting their articles published.”
Ron Unz has worked for English in the schools.
Even rich educated SWPL often have all sorts of misguided beliefs in language education.
If you don't speak English, there are plenty of good reasons to learn English, as it has become the world's standard language. But there is no measurable value to learning any other language.