This is an interesting, but thoroughly distressed, remnant of a derailleur. Clearly, it was once a copy of a 1950s Simplex Tour de France, and quite a decently engineered copy at that.
The main arm appears to have no branding on it (unlike a basic Simplex). There are also no rivet holes in the main arm to which a brass or enamelled nameplate could be attached (unlike a posher Simplex). The interest comes from the words embossed on the pulley cage. The outer plate reads "Zotta, mar. reg., Industria Argentina". I would translate this as "Zotta, Registered Trademark, Made in Argentina". The inner plate reads "5 Vel, Cat 3/32", which I would translate as "5 Speed, Chain 3/32".
The only Argentinian person who was willing to express an opinion, suggested that this derailleur dated from a period from the late 1950s to the early 1960s. You might well have guessed that yourself.