I gave you the proof of italian americans, vast majority of whom have never been to italy and dont speak italian.
here is some basic stuff, there are books written in aculturation and cultural assimilation by generation, all you have to do is read.
*http://www.danagioia.net/essays/eitalamer.htm
But each new generation of Italian-Americans finds its cultural links with the old country more tenuous. As the Little Italies disappear, and families disperse to the suburbs, the descendants of Italian immigration gradually merge their once sharply differentiated ethnic identity in mainstream America. Values change subtly but significantly. Intermarriage becomes the rule rather than the exception. If a third generation Italian-American speaks Italian, he or she usually learned it not in the kitchen but in college*
*Massey study shows rapid loss of Spanish language among Mexican immigrants in the United States
The authors found that although the generational life expectancy of Spanish is greater among Mexicans in Southern California than other groups, its demise is all but assured by the third generation. Third-generation immigrants are American-born with American-born parents but with three or four foreign-born grandparents.
In the second generation, fluency in Spanish was greater for Mexican immigrants than for other Latin American groups, and substantially greater than the proportions of Asian immigrants who could speak their mother tongue very well. In the third generation, only 17 percent of Mexican immigrants still speak fluent Spanish, and in the fourth generation, just 5 percent. The corresponding fourth-generation figure for white European immigrants is 1 percent. *