Polt is telling a fairy tale, a dream he had of how he became emperor of Rome 2000 years ago.
The time is cruel, bad luck if you are a slave. Germanikus is enslaved by the Romans. He is not very bright, but stumbles through the scenes and while a lot of the other slaves got killed sooner or later, he survives and makes it to the top.
The movie is just entertainment, it has no special meaning (as far as I can tell). And I admit: I did laugh at several points. The use of dialect doesn't bother me, I don't think that Polt can do without. But the dialect is not the source of fun in this film.
Most of the comedians playing other minor roles don't have the room to deliver fun or even a personality. They just appear and say some lines. The focus is just on Polt. Many flaws to be a good movie.
There are other movies out there which are really tasteless and disgusting. This one isn't that bad. It deserves 4/10. :-)