This idea extended through most of the 20th century, but was displaced by multiculturalism. I believe this is due, in large part, to the different ways in which American global power asserted itself. Until WW2, the dominant mode was imperialism and occupation, and the dominant mode of production was industrial (factories).

After WW2, new kinds of business emerged that would become the post-industrial society. Post-industrial business exists alongside (or on top of, I don't really know which) industrial society. Centrally controlled empire gave way to the cold war, where the east and west worked with local dictatorships or client states.

Under direct imperialism, the US (or Japan, or UK, etc.) would invade the country, take over its institutions, and re-educate the people, indoctrinating them into Americanism. With indirect control, the countries would retain their culture.

This change in empire coincided with the rise and institutionalization of multiculturalism. It could be coincidence, but I think it's just a natural byproduct. When India freed itself from British rule, it was no longer necessary for Britons to systematically enforce racism against Indians. Moreover, because the Indians sought democracy, they would come to be seen as allies who were let free after some tutelage, rather than as rebels.

Eventually, you face the phenomenon of the expatriate Irishman from London who yearns for authentic curry. There are hundreds of these guys in Santa Monica.

Multiculturalism is nice and fun, but it can also be a new form of imperialism. One year, the Chicano bookstore is pushing "Always Running" and hosting Aztec dancers, the next, it's "The House on Mango Street" and real estate workshops. The next year, it's mostly custom framed Diego Rivera prints (that one with the woman and the lillies), and the year after that, the only thing they're selling in t-shirts printed with the (german) iron cross "West Coast Chicano", and nobody cares what factory made the shirt.

And then the store goes national and shows up in some Hispanic business magazine!

I really shouldn't talk shit, because I'm Asian, and as a community, we are seriously more fucked up right from the start. We still desire to become part of the empire, and the will to resist is weak, even when we know our distant relatives are suffering, and the bombs didn't stop dropping until the 1970s.

English didn't become really significant in Southern California until after 1848, and even then, I doubt if Spanish was significantly displaced until after people really started migrating to the area in the 1900s.

So common was Spanish in the early 1900s that the teachers had to literally beat kids to get them to stop speaking it to each other. Nothing like a history of child abuse by the school system to politicize a language, huh?