Radler

This is of course what's known in English as shandy.

According to Wikipedia, the term dates from the great cycling boom of the 1920s, when an innkeeper named Franz Kugler created a bicycle trail from Munich through the woods that led directly to his drinking establishment in the small town of Deisenhofen, just outside the city. One June day in 1922, 13,000 cyclists arrived at the inn. In danger of running out of beer, Kugler began blending it 50/50 with lemon soda.

Wikipedia tells us that although the term Radler has been widely attributed to Franz Xaver Kugler, a mixture of beer and lemonade is documented in texts dating from 1912. Nowadays, Radler is consumed not only in Bavaria, but throughout the German–speaking regions of Europe. In Austria, it tells us, "it is common to use Almdudler instead of lemon soda for the Radler." Almdudler is a popular carbonated soft drink, made of herbal extracts, whose popularity in Austria is second only to Coca–Cola and which has been called the "national drink of Austria".

Wikipedia also points out that in northern Germany, a half–and–half made specifically of Pilsner beer and lemonade is known as an Alster (from Alsterwasser, after the river Alster in Hamburg). "Regionally [Wikipedia continues], the Radler and Alster may refer to shandies made with either citrus lemonade or orange lemonade, with the two terms either contrasting or referring to the same drink." (I take this to mean that the two terms are more or less interchangeable.)