"We are going to talk in English" is marked as wrong
That would be "nós vamos falar em inglês"
Your sentence makes me believe we are going to talk in english right now, and the Duolingo sentence is more of a near future, something we wish
we will talk english?
You can "speak" or "talk in" a language, but never "talk" it. However, speak is almost always used.
Why not: "Let's speak English"?
this would simply be "vamos falar inglês" without the nós, I believe.
I believe that "we are going to speak English should also be acceptable"
It is still not accepted ...
"We are going to talk English" marked as wrong?
I'm guessing it's because that sentence is grammatically incorrect? "We are going to speak in English" makes way more sense to me.
Actually, let me correct myself. "We are going to speak English" without the "in"