This shape of billhook machete is found mostly in the Balkans and it originates in similar Ancient Rome tools. It is used mostly to cut corn stems and other brush work, similar to a sickle.
The first method of rust removal was using cola, as lots of people suggested it. It kinda worked and took a really long time, a few days and needed a lot of wire wheel time to get to a decent surface. An advantage over the vinegar is that it keeps some of the original patina, so it might prove useful when restoring historical artefacts.
After the rust was removed a nice rustic pattern was visible on the tool, like a stem with leaves on the shaft part and some traditional patterns on the axe head. This suggests that it was a village blacksmith made tool in a rural part of the country and not a factory made billhook.