BERLIN — Germany’s election on September 24 is not just about who will become chancellor — it will influence the future design of the European Union. German voters have to decide whether Angela Merkel or her main challenger Martin Schulz — who lags by about 15 percentage points in polls — will lead the EU’s most populous country and push her or his vision on issues such as eurozone reform, defense cooperation and migration during the next four years. Also important for Berlin’s future position on Europe is whether any of the smaller parties end up in government as a junior coalition partner. Although Merkel has a comfortable poll lead and is widely expected to score her fourth victory in the national election, her conservatives will most likely need the support of at least one if not two other parties to govern. The same is true for Schulz’s Social Democrats (SPD), if the former European Parliament president defies expectations and overtakes Merkel. With six groups expected to ente..