Humans might evolve tools to lower cultural drift or get it to zero even, which is also needed I think if you want to build galaxy spanning societies, for preci

Humans might evolve tools to lower cultural drift or get it to zero even, which is also needed I think if you want to build galaxy spanning societies, for precisely the reason you state. E.g. you could have many jobs in society be done by machines, have humans be raised by them, interact with them on a daily basis, etc. If you want to prevent language drift, you could have these machines speak only one specific kind of language. That way, all the cultural works of the ancestors are still directly accessible to everyone without translation.