This is less a working derailleur and more a delicate piece of origami. The steel sheet used to make it is so thin that it is hard to believe that it would ever work reliably or even work unreliably for more than a few days. The hanger plate is 2.2mm thick, which compares with 4mm for a standard Shimano hanger. I believe that the stiffness of a steel plate varies as the cube of its thickness - so the Shimano hanger will be a mere 6 times as stiff.
I know nothing about the history of this derailleur or about its manufacturer - except that I got it from Brazil and have been told it is Brazilian - which seems reasonable. There is no branding on it anywhere.
If it does date from the 1990s, it is hard to believe that it was worth the effort - in those days you could buy a surprisingly respectable derailleur from Taiwan for a few pennies.