We're familiar with Ancient Athens and while not a democracy, Rome's Republic at least had a democratic element, but what about the rest of the pre-modern world? I've heard it said that Carthage was arguably more democratic, that Scandinavians during the Viking age were fairly democratic... as supposedly was Xenophon's army and many of the pirate ships during the golden age of piracy. Was it seen as a normal thing in smaller social structures? Was it still vary rare or do we think it was pretty common?
I don't know how to address the question as a whole, but for the pirate part - that aspect is overstated. Pirate crews were not as democratic as many factoid and humorous information articles websites present them as. Pirate crew organizations have been severely over generalized over time. They borrowed their ideas for organizing crews from various aspects of society they had previous experience in before becoming pirates. This post (in particular the 2nd part) addresses that issue about democracy. Blame romanticism, desire for simplicity, agendas to present pirates and ideal opponents to period capitalist systems, faulty (and lazy) historical research, and people being accepting of this "stellar pirate democracy" stuff since they could picture themselves doing that.
So my question here is what you mean by democracy? It is a common theme in some scholarship on pre-colonial Africa to play up democratic institutions in the selection of leaders: in some societies, for example, all candidates from within a royal lineage would be presented for consultation with the general populace to help select among them. I'm not sure this is democracy per se, however. It would be easier to answer your question if we knew whether you meant some sort of formal voting structure, or just loose (almost anarchist or syndicalist) communalism and power-sharing, etc.