Germany-born Nmecha played only a handful of games at his parent club Manchester City before impressing this season on loan at Anderlecht. The Belgian club is coached by former City grea Vincent Kompany.
Germany beat Spain 1-0 in 2017 andEngland 4-0 in 2009 in their other two U21 title-winning finals appearances.
The senior German team are preparing for the upcoming 2020 European Championship, which was rescheduled from last summer due to the coronavirus pandemic.
Joachim Löw's side was drawn with France, Hungary and Portugal in the pot of Group F at the EURO.
Portugal defends their title in the EURO and will play Germany in Munich on June 19.