This is wrong in almost every respect. Assimilation is not defined simply by "obeying the rules of a system outside the home." It is defined by entry into a culture, such that members of the minority group are absorbed into the dominant culture "to such a degree that the assimilating group becomes socially indistinguishable from other members of the society."
https://www.britannica.com/topic/assimilation-society ;
cf.
multiculturalism.
German-Americans maintained a distinct culture, with
schools conducted in german, religious
services conducted in german, german cultural festivals,
all-german army regiments, and
german-language newspapers, for approximately 150 years after Franklin made his pronouncement that they would not assimilate. That's the opposite of assimilation.
(Although some of these still exist, they were mostly stamped out forcibly around WW1, as has been discussed in thread.)
Where Franklin
was wrong was his idea that different cultures could not coexist, and his conclusion that the outcome would be to "Germanize us" or "our Anglifying them." That conclusion didn't occur organically, and might not have occurred at all had the government not forced the issue.