Álvaro va a trabajar en un bar este verano.
Sometimes the English is contrived to make a point in relation ta a specific lesson.  These can be quite false.  To say Alvaro is working in a bar this summer  means it is now summer and that is what Alvaro is doing.  If asked:  "What is Alvaro going to be doing this summer?" the response could well be : " He's workking in a bar this summer" meaning that is what he is going to do.  
Why not give the English as " Alvaro is going to work" OR " is going to be working in a bar this summer". ?.  it is less artificial and makes much more sense.  (And is less irrtating)