Put the potato cubes and 1 teaspoon salt in a saucepan, fill up with cold water and cook for 10 minutes. Drain, drain, transfer to a bowl. Add celery, paprika and cucumber cubes, red onion and eggs and mix everything well. Mix the mayonnaise with the mustard and vinegar in a small bowl, season with salt and pepper and carefully fold into the salad. Cover and let stand in the refrigerator for 3 - 4 hours. Serve the salad at room temperature.