From 1320–1330 it was part of the domain of the Grand Duchy of Lithuania. Later it was owned by the Radziwiłł family, which transformed the city into a center of the Polish Reformed Church with a Gymnasium that existed till 1918.Following the 17th century the town became famous for its manufactories of kontusz belts, some of the most expensive and luxurious pieces of garment of the szlachta.
Alex, that's an absurd argument, imo. Parts of Greece were Serbia in the 14th century. Good part of Ukraine was Polish over the course of history and Gdańsk was German (Danzig), as was Russian Kaliningrad (Königsberg), and so on.
We don't spell names of formerly Serb-held territories in Greece the Serbian way, nor Ukrainian names the Polish way. Nor do we list Danzig and Köningsberg on our maps.
The fact that every Tom, Dick and Harry claimed Slutsk at one time or another doesn't justify spelling a Belarusian city the way it was spelled in Polish.