The OP mentioned that the fork was English threaded, yet the steerer tube measures 25.0 mm. As Charles Wahl notes, the frame cup inside seat is pretty much universal.

I will share that if you are willing to live with a class B or C fit, you CAN run something other than a French metric headset on a French 25.0 steerer tube. My Allegro came to me with a Campagnolo 25.4 x 24 Italian threaded headset that a previous owner had fitted to the Nervor 25.0 x 1 steerer. It almost worked, though it was predictably a teensy bit loose, and he'd left out stuff like washers and a centerpull hanger to get something that needed 42 or so mm stack height to fit onto a steerer cut for a 33 mm-ish headset. I wound up replacing it with the bottom half of a generic Tange headset to fit the monkeyed-with fork crown set and the top half of a generic Motobecane headset that has about the same dimensions as a Stronglight P-3. It works much better, and I was able to carefully thread the French bits back on and have had no issues with it. Measuring stuff with good calipers makes life a lot easier.

All of that said - I think you have some sort of French bike with a Swiss threaded bottom bracket that someone has force-fitted with an English headset. Juvela mentioned Prugnat 62/S lugs with a Vagner PC fork crown and a BB shell by Gargatte (Raccords Gargatte Freres, to which I would add that the dropouts look to me like Nervex stamped units just like the ones on a zillion entry and mid-line French bikes, including this Liberia. All of this is very French. Bertin has been mentioned - did they ever use Swiss threads? I bet other makers used similar seatstay top treatments. Is that swaged and crimped?