Family name Koslak (Koslak 
) , in all the world, is a rare surname. The surname Koslak is habitual in Turkey, where it is a rare surname, Poland, where it is a very rare surname, and Germany, where it is an extremely rare surname. Not in comparison with a country's population, the name is most common in Turkey, Poland, and the United States. Also, Koslak is the forename as well as the last name.