rob006 Do you have plans to adjust other translations in the same way? Only first import to Weblate is safe, further adjustments will need to be done through Weblate, so it would be better to do as much as possible before import.
To make this clear, what I have pushed are changes to the current translation pack, already on Weblate. This is not the formal translation.
About the formal implementation, I have successfully modified the LanguagePack.php to 'override' the informal translations that change in a formal context, if the user has toggled them on. It is simple enough and much preferrable to splitting the language into two extensions. Only question for you would be, does Weblate handle the export of unfinished translations correctly? It should not output strings that are missing. (edit: i believe this is already the way it works, so this method would not require further work to implement)
edit2: Pushed formal toggle implementation to github. The way it clears the cache may be a bit hacky, if somebody smarter than me has a better way to do it please let me know. It also duplicates the entire LanguagePack.php, as the methods are all private and inheritance cannot be applied instead.
