At the 2009 European Athletics Indoor Championships, he finished fourth in his heat but did not progress to the final. Schlangen took the 1500 m at the 2009 German Athletics Championships and represented his country at the 2009 World Championships in Athletics. He retained his national title at the 2010 German Athletics Championships and attended the 2010 European Athletics Championships. Despite being an outsider for the podium, he took the silver medal in the 1500 m behind Arturo Casado, who won in his native Spain.