Robert Lane Greene asks, why “did previous waves of immigration not threaten English, while today’s does?” He cites a study focused on Hustisford, a town in Wisconsin that was representative of many German immigrant communities in the US:

Almost a quarter of Hustisford’s population (over ten years old) was monolingual in German in 1910. Of that share, a third were born in America. Of the German monolinguals born abroad, a majority had been in America for more than 30 years, having immigrated during the height of the German wave. In other words, in small-town America a century ago, it was perfectly possible to grow up, or to live there for decades after immigrating, without learning English.

He thinks today’s immigrants are more, not less, proficient in English:

[I]t is nearly impossible today to grow up in America without learning English. One study of more than 5,000 children in the Miami and San Diego areas (thick with Spanish-speakers) found that 94.7% of Latino middle-schoolers who had been born in America spoke English well. The authors concluded that “knowledge of English is near universal, and preference for that language is dominant among most immigrant nationalities. On the other hand, only a minority remain fluent in the parental languages.”

My thoughts on language and culture in America here.