This is a very bad, off-metal copy of an Austrian Maria Theresia Thaler.
Maria Theresia died in 1780, and the Thaler has not been a unit of Austrian currency for at least a hundred years, but the coin is still produced with the date 1780 as a silver bullion coin. In this capacity, it was one of the most widely used and recognized silver coins in the world. It would be accepted in Africa, China, Europe, the Middle East... so there is a lot of motivation to create a fake copy. What size is it? It could also be an off-size replica made for tourists rather than a counterfeit intended to be spent.