Is stall recovery training mandatory for Airbus pilots?
According to the official investigation report, both the flight crew on this flight had received stall recovery training, but not upset recovery training, on the A320. The Flight Crew Training Manual for the A320 (issued by Airbus) did not mandate upset recovery training. The operator's training manual (issued by Air Indonesia) did mandate upset recovery training, but it was not delivered by the airline for pilots of the A320 because of Airbus's statement that it was unnecessary. Only upset prevention training was given. Both the below are from the linked report:


  The  approved  Operation  Training Manual covers  the  upset  recovery
  training  in Chapter 8. The  module  consisted  of ground and simulator training. The ground training provides the flight crew with the background, definition, cause of  aircraft upset, aerodynamic and  aircraft systems in 
  relation with aircraft upset. Recovery methods consider various aircraft attitude and speed including post upset conditions. 
  
  The  upset recovery training  had  not  been  implemented on Airbus  A320 
  training, since it  is  not  required  according  to  the  Flight  Crew  Training  Manual  and  has not been mandated by the DGCA.


and later


  The Upset Recovery training was included in the aircraft operators training manual. The aircraft operator advised the KNKT that the flight crew had not been trained for the upset recovery training on Airbus A320, and this referred to FCTM Operational Philosophy: “The  effectiveness of fly-by-wire  architecture,  and  the  existence  of control  laws,  eliminates  the  need  for  upset  recovery  maneuvers  to  be  trained  on 
  protected Airbus”. There was no evidence of DGCA findings for this incompliance of training.


Upset aircraft is where the attitude or airspeed is greatly outside the normal flight envelope, such as might happen after a mid-air collision or loss of control, or (as in this case) prolonged wrong inputs when fly-by-wire is disengaged. A stall is not necessarily an upset aircraft condition.

The report also notes that the stall recovery training doesn't necessarily cover the developed stall, but rather recovering when the stall warning sounds before actually reaching the stall. The exercise is carried out from level flight by reducing airspeed and pitching up progressively to trigger the stall warning, and then pitching down to recover. (This is the same way stall recovery is taught to private pilots in smaller aircraft.)

Recovering from a developed stall where the aircraft's attitude is level but it is descending rapidly (stall at zero pitch) is not mandatory training (p119), and this is the situation the flight crew were unable to recover.

As there are too many crashes resulting from unrecovered stalls, the whole industry has worked together to produce better training programmes. One of the Safety Actions resulting from this crash is that Air Indonesia now gives upset recovery training to all its pilots, to comply with its own policy. In addition, the airliner manufacturers have produced a new training aid (applicable to most airplanes) for teaching upset recovery, and Airbus has already issued an Operations Training Transmission with instructions for carrying out suitable simulator training.