Ironically, "Ваня, говорите по-английски" showed up just before this one!
I assumed this was directed at poor Vanya, and Duo didn't need to put his name in again.
I wonder if he's put on his shoes yet....
Kaj vi faras ĝuste tion (krokodilas)! Vi devus skribi: Ĉu estas esperantistoj ĉi tie?
Why is the phrase "по-английски" and not "по-английский"? Why is й dropped from the adjective?
To describe which language you speak we use adverbs (по-английски, по-японски) or adverbial phrases (на русском, на японском, на пирахан). There is no way to use the adjective directly with speaking. Говорить only attaches things you speak as objects (not the language you speak them in).
However, in Russian you can say that you "know" the language. Then you can use английский or английский язык as a direct object of the verb.