There's almost 0 state efforts to preserve the cultural identities of immigrants of any kind
When people celebrate "diversity" in the West, it's just eating shawarma, drinking boba, watching Anime, listening to kpop, and eating at an Ethiopian restaurant. Pure commodification and consumerism masquerading as celebration and promotion of foreign cultures
Or you'll have people fetishizing about spicy latinas, lightskins, and Asians like they're fucking Pokemon cards
In Australia some non English languages were punished, so I don't think that is such a good example. In the US you had sinophobe actions and the japanese internment camps, you had cultural genocide against kids speaking some languages, in Canada this went on bis at least the 90s. On some school yards there is a English only policy (some for Germany, were in some cases it exists formal or informal).
While I do see that you would like to make a point about the level of how significant it is and also how there are processes which happen that you would like to not have labeled as such a negative thing, or are processes you label as just existing, I would like to highlight that it is a much bigger and structural relevant problem, with continuity to before.
Even in terms of dialect homogenizations linguists do make points about whether to save or record them, nationalists and alike are arguing for keeping their (but not others) dialects up.
In terms of cultural and classist genocide against non Birtish accents I would like to mention the corporal punishment dished out against both orphans but also non Oxford English speakers on boarding schools in the UK in the 50s and partially 60s, but also that similar things happened in France, which had colonial characters, too. In terms of elite prep schools the forced homogenization in terms of speech and language was a colonial and imperial tool that furthered genocides, cultural and physical ones.
i didn't say anything about the british?
ffs the fact that indigenous people were genocided into speaking english in the first place has nothing to do with their english accent changing over a period of years because the moved to a different settler colonial nation-state.
someone born and raised in mexico city who moves to uru uru and lives in bolivia for 30 years will start to sound bolivian at some point unless they deliberately avoid interacting with their neighbors. their kids will go to bolivian school and learn bolivian spanish instead of mexican spanish. the difference between this person i made up and my old indian classmate's kids who probably won't learn hindi is that those kids also won't learn any lakota or whatever either.
i'm not going to fucking say hworsch instead of wash just because my grandmother did, but i spent a week doing work training as the only non-southerner in a group of 10 and I was unconsciously adopting some of their inflection after a few days of not hearing my own dialect.
genocide requires intent and a specific target. we're on fucking hexbear i'm not denying that genocide happens or that deliberate systematic oppression of languages is part of some genocides but assimilationism isn't that on its own, even as racist as it is here, it's not fucking geocide when the children of immigrants aren't perfect copies of their parents.