And as it happens, all the evidence suggests that it takes recent immigrants a generation or so less to learn English than it took the German, Polish, or Italian immigrants of the early 20th century. True, first-generation immigrants are often slow to learn the language, particularly if they live in ethnic enclaves and work at menial jobs. But their children are virtually all English-speaking, unlike the children of first-generation immigrants a century ago.

— Geoffrey Nunberg, Where our mouth is

This point could have been made stronger: one century ago, new immigrants to America encountered a barrage of cultural institutions that encouraged them to retain their native languages, to stem the tide of Americanization and the loss of ethnic identity. The Swedish Lutheran Church even opposed a measure in the Wisconsin state legislature that would have mandated some (an hour or two) school instruction take place in English.