Next to the Festo programming device(s), I found this one, about the same age (I think 1980). There are also some rare keys. Nice key alignment and display.
Musée de l'automatisme
There’s another photo on this small museums page showing a narrow external UV erasing device which can be attached to the left
There’s also the manual on the official Siemens site (at least in German) including schematics and programming examples (I haven’t read it all)
PG obviously stands for Programmiergerät (programming device), note the French name here Console de programmation.
Programming is for the SIMATIC S5 devices, language is STEP-5 (predecessor of STEP-7 which I think is still the global leader and now also used by Festo.
I won’t buy this as it’s still expensive and not even rare. I think 8085 based.
There are other programming devices for S5 like the PG631, PG675/685 which are still portable but has a CRT monitor, disk drives and full keyboard.
I mentioned the keyboard here
and other PLC parts here
Siemens SIMATIC S5
Also of interest this forum post including ROM dumping (in German).
Also of interest are training PLC devices. There are many, especially in Asia.
A simple one with a nice design is this one by SS Lavs India. Reminds me of the Tandy x-in one kits (box, color design)