B737-800 Captain reported ground personnel opened cargo door during pushback without communicating; resulting in an expeditious engine shutdown. Captain also reported communication difficulty due to ground personnel lack of English.

Narrative

During push back from gate XX at JFK; we were cleared to start both engines by the tug operator. The FO had begun to start ENG # 2 first; several seconds after fuel was introduced; we received a Master Caution light in the flight deck for DOOR and had a cargo door caution on the overhead panel. I asked if the Cargo door had opened in which the tug operator advised us that a ramper had opened the door to add a last-minute bag. I immediately advised the FO to shut down the #2 ENG and asked the tug driver who gave the ramper permission to open the cargo door especially when the engine was running. He said he tried to tell us that they were going to add another bag to which I said we had already been cleared to start the engine and that he had not even asked us to set the parking brake nor told us of anyone opening the cargo compartment. I advised him that it was extremely dangerous to access the cargo door while the engine was running and against operating procedures and that we were still in the middle of the push with the parking brake off and in the start sequence. I advised operations management of the incident and verified that the last-minute cargo was captured in our load closeout.Cause: Tug driver did not speak English very well; nor did he communicate to the flight deck his intentions of allowing someone to access our cargo compartment during an active push back. Recommend all ground crew involved in the incident to repeat training on the importance of aircraft safety and standard operating procedures during push back.