Dozens of strings of lanterns are connected to 220-volt bulbs. What wire should I use? How to connect them quickly and manually?

2.5 mm will do. I counted 80 50W lamps. 4000 w/220v =18.18a, 2.5mm safety current 20A, which is enough. If it is temporary, it is recommended that you use aluminum wire, but it should be 2.5mm thicker 1.5 times.