LondonClassic
Retro Guru
Yep. Peugeot moved over to ISO standards in the 80s...but the exact when of this is not clear. And because they were a ginormous manufacturer their inventory was mixed ISO and French threads. I reckon by about 1985 they were fully ISO but in that 82-85 window its pot luck and sometimes you might see different threading on the same bike.French stems are 22mm. Normal standard stem is 22.2mm. French headset, bottom bracket, freewheel, pedal threads are different. You could have a mixture of the above on one frame. I've got a Peugeot which has.
From the graphics I reckon your bike is 1982 or 1983. Maybe get hold of a 1" ISO threaded headset top half and see if it threads onto the fork. Maybe your LBS can help you out if you ask nicely.