Most languages I know have formal vs informal "you" but I've never seen formal vs informal "we" except in French.
Si quelqu'un prend une glace, je vais lui demander "T'as pris quel parfum ?" mais là si on vient me demander à quoi sont mes nouilles, je vais plutôt répondre "Goût boeuf sukiyaki." que "Parfum boeuf sukiyaki.", le contraire me semblerait bizarre mais peut-être que c'est juste moi et que les deux sont parfaitement interchangeables.
I read a few times that native speakers can't speak their language wrong. But what about those kids who moved to another country when they were between 5-10? Let's say they spoke at a native-level but then stopped completely to better assimilate in their new country. In their adulthood, they want like to reconnect with their early years but too much time has passed without any practice and they can't even get the grammar right.
Are they still native speakers of Language A? Or is it Language B now? Or have they lost all eligibility to be called native of either language?