Car sale from private to private to Denmark. Responsible court

I sold a vehicle with a purchase contract to Denmark. A down payment was agreed and the down payment was made by the buyer. As delivery date from vehicle location Germany it was agreed that the collection of the used vehicle can take place if the new vehicle ordered by the seller was handed over to him. However, this took too long for the buyer. The buyer from Denmark has now announced that he wants the down payment back. I then offered him that He can pick up the vehicle immediately and the remaining payment is due. There is no reaction According to German law, I could now set a period of 14 days for non-payment and then file a lawsuit if the buyer does not pay the vehicle and loses it. Since the buyer is Danish, however, the question remains: Is a court in Germany competent for the reminder or possible lawsuit or should the lawsuit be filed in Denmark. Can someone help here in the forum? Thanks for a Info!