"After one year, the students will know English."
Translation:Bir yıl sonra, öğrenciler İngilizce bilecekler.
"I speak English." in English usually means "I know English.", "I can speak English.". In Turkish it's "I know English.", "İngilizce biliyorum.".
"know" or "speak" (being able to speak) = "bilmek".
But "İngilizce konuşuyorum." has only the literal meaning - the act of speaking the language. I don't think it implies knowing English or the ability to speak it.
"konuşmak" = "speak" (actually speaking).
"Bir yil sonra ogrenciler ingilizce konusacak." means that the students will actually speak the language at some point in a year, not that they'll know it in a year.
Quantifiable time phrases + time adverbs don't generally take case endings. Case endings are reserved for events and other specific unquantified things.
So "beş dakika sonra" = five minutes later vs "ameliyattan sonra." = after the surgery.
Or, maybe to make the point a little clearer, "bu yıldan sonra" = after this year vs "bir yıl sonra" = one year later.