It is not so much a matter of changing habits, often migrants such as my parents take their elderly with them to the new country, leave their kids with them, and go to work, so their elderly parents get stuck in a new country, without speaking the language and being basically the only guardian their grandkids have.

Hell, my grandmother went from being a teacher in the old country, to a nanny who never managed to learn how to speak the local language, despite learning how to read and write in it, to a college level.

Most languages are far from phonetically true, and a lot of languages lack written accents. Things aren’t as black and white as you make them seem.