And you shouldn't worry too much about mistakes but repeat sentences slowly and correctly, without too much focus on what is wrong. These roots are very deep. The same goes for culture. It is entirely possible to be reasonably polyglot and polycultural at the individual level and at the community level. It is immensely enriching, like living several parallel lives.
Some immersion is needed in the significant other and the neighbor or friend.
Schooling is a poor substitute for those, but certainly has a role to fill. Let's take a look at Hawaii, a place with extraordinary cultural diversity and symbiosis, all at the expense of the Hawaiians. Hawaii is one of the few places on earth where no national group can claim to be the dominant group numerically or in terms of cultural or economic power. All are minorities. Even if many no longer talk their languages of origin, all groups have preserved cultural competence to a considerable extent, for instance with regard to the rites of naming, marriage and burial.