From what I've seen the South American countries tended to either purchase surplus kit from abroad or go as cheap as possible using local materials. As pointed out above, this is a high quality piece. Germans keep coming back to this discussion for some reason
I like the idea this was a 1940s or very early 1950s German made piece prior to standardization practices in the 1950s. During the 1940s the British and Americans armed para military units under the guise of police (they did perform police duties). They were organized along military lines and even had heavy infantry weapons like Bazookas and MGs. A little more than necessary for Biergarten brawls or pulling over speeding motorists
Not much is known about these units or what they used for equipment.
I have a picture of a 1940s unit armed by British. They use a mix of all kinds of crazy stuff, including British weapons and German made magazine pouches for their Brens.
No doubt the Soviets did the same thing. If they were issued PPSh 43s, which the Soviets wanted to get rid of (there was a lot of politics around the PPSh 43!), maybe it could be for them. They for sure used StG 44s early on.
So yes, I think until we have better information I'd be comfortable labeling this "early post war West German" or perhaps even "early post war East German".