The phrase "in English, please" has different meanings in different social contexts. In one context it might mean literal English language, and in another it could imply a response in layman's terms.
I recall a scene from Star Trek, which humorously shows contextual confusion:
Kirk: (in battle) Status, Mister Spock.
Spock: Captain, the deflector field ionic beam is over-critical.
Kirk: English, Mr. Spock.
Spock: Am I not using the correct form of the English language?
Kirk: Spock!
Spock: Our shields will be down in ten seconds.