why is you all not accepted as a translation for jullie. It is perfectly acceptable in english and seems a more unambiguous translation
Probably because, although very common and useful, y'all and you all are generally stigmatized as not being 'proper' or 'standard' English. Personally, I think if they're accepting British-only sayings (like dear=expensive), then y'all should be accepted too. But they may be trying to translate the Dutch words into a more 'regionless' version of English... In which case, no.
Well natively I speak NZ english which is very closely derived from british english. Although you would rarely hear "y'all", "you all" as a disambiguation is very common. I.E. "you need to go do your homework" vs "you all need to go do your homework".
Why is "why are you not leaving" not accepted? Usually phrases and verbs work just like in german. Is this one different?