"This is all very sudden."
Translation:Das ist alles sehr plötzlich.
Alle das isn't grammatical, it should be All das or Alle die, maybe even Alles das (usually shortened to all das). It's a problem of number, sg. vs. pl. As the English sentence is in singular, "Alle die sind ..." will probably not be accepted, so you can just say "All das ist sehr plötzlich" as an alternative to Duo's version. Also dies instead of das should be fine.
Isn't that more like "All that is very sudden"? I.e. with the emphasis on the other part?
No, for me there's no difference in emphasis between all das and das alles. The former is a bit higher level of language, but means the same.
But here we don't have das alles, do we? With the verb in between them, I thought that alles is acting here as an intensifier for sehr plötzlich.
In German, (in my book anyway) we don't imagine the sentence "Das ist alles sehr plötzlich" as "This is --- all-very-sudden"; only as "All-this --- is very sudden". In other words, "alles" doesn't refer to "plötzlich" (as would be possible in English, e.g. "He was all red in the face / smug / alone") and therefore doesn't intensify it. Which also means that I agree with Max.Em about "das alles" being interchangeable with "all(es) das" (and everything else he said, for that matter).
As the German version of "all [adjective]" I'd suggest "ganz" ("Er war ganz rot im Gesicht / ganz allein") or, more colloquially, "total" ("Er war total selbstgefällig"). Or even more colloquially, which you really shouldn't use in formal company: "voll" ("voll rot im Gesicht", doesn't work for "allein").
You mean like allzu? Das ist mir allzu plötzlich? But alles/all always refers to das.
"alle" would be plural, but "das" is singular, so it's followed by the singular "alles". In both English and German, you treat "all this" (as well as "everything / alles") as a singular thing (you don't say "All this are very sudden" or "On this old TV, everything are grey").
Two examples for plural: "Can you find me a different knife? All of these are blunt." = "Die (or: diese hier) sind alle stumpf." (...and, for the record: "These are totally blunt" = "Diese hier sind ganz/völlig/total stumpf"); "Let's pluck some strawberries! ...Oh no, they're all still green." = "Die sind alle noch grün."
It is correct German, but it's also a bit more similar to "All that is very sudden", however the meaning doesn't really change imho.
Why not dies or dieses idk im confused why theres not a proper way to say this auf Deutsch
"All very sudden" in English has all acting as an intensifier = really very sudden or truly very sudden. I think the German means more like "All of this (situation) is very sudden", though, to be fair, I think the English can mean that too.
As a native English speaker, I’ve only ever interpreted the English sentence to have the latter meaning.