why this is wrong ?"you speak english"?
Because this is a question and '"you speak english?" is an informal way to ask a question, so Duolingo doesn't accept it.
Duo does accept informal answers for many problems I think.
For me too. Now I don't know what's the real problem...
It can also be - 'Tu parle anglais'
Tu parles anglais would be the correct way of saying it, since you need that -s when it's about you.
is vous used for formal questioning' because vous is also for plural you
yes i doo