国际世界语协会
After 1913 he was a member of the "Komitato" of the World Esperanto Association (UEA), the Esperanto leadership group later known as the "Estraro". In 1928 he became "komisionano" and vice-president of the UEA. Then, when Eduard Stettler was president, Karsch often stood in for Stettler, who was in ill health.