I though אומר was "talk" and בדבר was "speak."
Not quite, אומר is "say", מדבר is both "talk" and "speak". By the way, how would you define the difference between "talk" and "speak"? I'm not a native English speaker, and to me they are synonyms.
They are pretty much synonyms. The difference, if any, is subtle.
One difference is when discussing a language, we typically use "speak" instead of "talk". "Speak" is also a little more formal, such as someone giving a lecture is invited to "speak", not just "talk".
Why not "אנו לא מדברים על זה"?
Yes, should also be correct. But here it's in the sense of "one speaks" or "you speak", like in German the word "man", there's no english word for that.
Hm, ok! I think I got it! Like the use of 'se' (reflexive pronoun) without a subject in Portuguese(, Spanish, French...): "Não se fala sobre isso" (It can be expressed in other ways, too, but I think it is the more "standart" way to do it...)
Oh right, reflexive pronoun. That's the word for it!
So in German it is a reflexife pronoun, too?
Yes, I guess so.
According to my Michaelis GE-PT Minidictionary: man [man] Indefinitpron 1 a gente. 2 alguém. man spricht Deutsch fala-se alemão
No, in German it's not reflexive: 'man redet'.
Man redet sich would mean one talks to oneself.
I would still claim that אנחנו or אצלנו have to come in the beginning but I accept the fact that the course developers do not agree with me.
It seems like the English translation should be "no talking about that" with "there's" implied, but I'm not getting the "We".
Without the"we" the sentence sounds like a command...