What is the type of German Duolingo teaches?
Is it West or South German? Please let me know!
The term "Hochdeutsch" is a little misleading; whenever I read it, I think of the German spoken way further south to me. But it is also applied in the way OmegaGmaster uses it, to mean "Standard German". The wikipedia article is quite interesting: https://en.wikipedia.org/wiki/Hochdeutsch
"Hochdeutsch", as "Standard German" https://en.wikipedia.org/wiki/Standard_German, is spoken and understood in all of Germany. In various regions, there are dialects, but in school, we all learn "Hochdeutsch", it is the language used in TV and in official documents.
So, with the German taught on Duolingo, you can expect to be able to communicate in Germany.
No, certainly not. The sentences I've seen on Duolingo are just normal-language sentences that everybody uses.
I think as a learner of a language, it's always safe to err on the "rather standard" side of the language. In order to get the more slangy expressions right, one has to have a good feel for the normal language.
I always found it hilarious when I heard some of my fellow German learners of English trying to sound like Gangsta Rappers. ;-) It gives a very unnatural impression.
In my opinion, it is much more natural to sound like "a polite person who is learning the language".