The data I saw is that by the third generation, only a few percent speak the language of their grandparents' country, and most marry outside their nationality.
In the US, Italians, Irish, and Germans, as just a few examples, all were treated as unassmilated aliens. People say the same things, generation after generation about newcomers. If you moved to a country with a different language and culture, you might make an effort to learn the language but you would still think, read, etc. in your native language. Your kids would know both languages; their kids would of course speak the language of their surroundings.
What solves these problems is a fundamental belief in freedom for all. People don't need to speak your language to be your equal and be just as human, with the same rights as you.
This was certainly true of my Polish ancestors. My great grandfather arrived at age 19. He never really became fluent in English but could get by when he needed to. My grandfather spoke both Polish and English but only spoke English at home once he had school aged children. My father really only knew the Polish swear words and I know a handful of Polish phrases that only get used amongst family at Thanksgiving or Christmas. Don’t ask me to write them down. I’ve only ever heard them verbally.
Italians, Irish, Germans in US are bad examples, because Americans and Western Europeans are basically one and the same culture, the only significant difference being the language spoken. I suppose integrating Chinese or Indian people might take much longer.
In fact, they were seen as very different cultures and the exact same things were said about them. Only in hindsight do people say what you are saying (and in hindsight they will say the same about today's immigrants). In fact, the world has never been smaller or more homogenous - people in countries all over the world dress like us, are exposed to our culture a great many already speak English. Before you spread damaging misinformation - there are few evils inflicted by and on humanity than those based on these prejudices - shouldn't you know what you are saying? Shouldn't we talk great care?
Here's Benjamin Franklin (Palatine refers to the Holy Roman Empire or Germanic regions, depending on the source):
"[W]hy should the Palatine Boors be suffered to swarm into our Settlements, and by herding together establish their Language and Manners to the Exclusion of ours? Why should Pennsylvania, founded by the English, become a Colony of Aliens, who will shortly be so numerous as to Germanize us instead of our Anglifying them, and will never adopt our Language or Customs, any more than they can acquire our Complexion.
Which leads me to add one Remark: That the Number of purely white People in the World is proportionably very small. All Africa is black or tawny. Asia chiefly tawny. America (exclusive of the new Comers) wholly so. And in Europe, the Spaniards, Italians, French, Russians and Swedes, are generally of what we call a swarthy Complexion; as are the Germans also, the Saxons only excepted, who with the English, make the principal Body of White People on the Face of the Earth. I could wish their Numbers were increased. And while we are, as I may call it, Scouring our Planet, by clearing America of Woods, and so making this Side of our Globe reflect a brighter Light to the Eyes of Inhabitants in Mars or Venus, why should we in the Sight of Superior Beings, darken its People? why increase the Sons of Africa, by Planting them in America, where we have so fair an Opportunity, by excluding all Blacks and Tawneys, of increasing the lovely White and Red? But perhaps I am partial to the Complexion of my Country, for such Kind of Partiality is natural to Mankind."
In the US, Italians, Irish, and Germans, as just a few examples, all were treated as unassmilated aliens. People say the same things, generation after generation about newcomers. If you moved to a country with a different language and culture, you might make an effort to learn the language but you would still think, read, etc. in your native language. Your kids would know both languages; their kids would of course speak the language of their surroundings.
What solves these problems is a fundamental belief in freedom for all. People don't need to speak your language to be your equal and be just as human, with the same rights as you.