What if countries like the US or the Spanish and Portuguese ex.colonies decide to effectively officialize the local dialect and try to develop the language completely independently from the motherland?
This is already the case but they are still called Spanish, Portuguese and English. You don´t necessarily need to make them completely different, having a situation where it´s basically like Serbo-Croatian is fine, even if I´d like there were enough differences to back it up.
Native language could count but it´s a cheap way to do it, given the challenge is to develop a language from the motherland. A creole or pidgin becoming official is fine.
POD after 1700. Bonus point if the language of the US is officially called Murican.