The usual bestseller lists in Germany are published by Der Spiegel and are often dominated by crime writing and translated (genre) fiction, which is not so much my bag. But look, I've found this alternative list compiled by the Berlin-Brandenburg station radioeins: die radioeins-Bücherliste. It comes out every Monday and consists of titles that sell well in bookshops around the region. This week it's topped by Sofi Oksanen and Robert Seethaler – two writers I approve of – and contains both fiction and non-fiction, including a diatribe against lazy teenagers translated from the Italian.
The Spiegel list is more accurate, compiled from electronic sales data from 500 bookshops around Germany as opposed to radioeins's vague "asking bookshops in Berlin, Potsdam, Cottbus, Frankfurt/Oder, Brandenburg and Rheinsberg". But the radioeins list is more personal, I suspect, reflecting what you might be advised if you asked a local bookseller for a tip. Sympatico.