A pelvis injury to FIFA World Cup-winner Weidenfeller means Langerak will keep his place in Dortmund's goal for the clash at Munich's Allianz Arena having played in Sunday's (AEST) 2-0 league win at home to Eintracht Frankfurt.
The Munich showdown will be a repeat of both the 2012 and 2014 German Cup finals in Berlin when Dortmund routed Bayern 5-2 three years ago - in that game Langerak came off the bench early on after a Weidenfeller injury.
Pep Guardiola's Bayern took revenge with a 2-0 extra-time victory in Berlin last year as it won the league and cup double.
With six caps for the Socceroos as Mat Ryan's understudy, the 26 year-old Langerak has played in six Bundesliga matches, four German Cup games and a single UEFA Champions League match this season.
He briefly replaced Weidenfeller as Dortmund's first choice goalkeeper just before Christmas.
After Dortmund started February bottom of the Bundesliga table following a disastrous set of results, the 2011 and 2012 German champion has climbed up to eighth after their win over Frankfurt.
It is just three points from the UEFA Europa League places for next season.
With Weidenfeller out for the next two weeks, Langerak will also play in Dortmund's next two league matches against fellow European candidates Hoffenheim and mid-table Hertha Berlin in the coming weeks.
