A knee injury to Borussia's captain and shot-stopper Roman Weidenfeller has handed the 22-year-old Langerak his German league debut at Munich's Allianz Arena in front of a sell-out 66,000 crowd, having joined Dortmund last July.
"It doesn't matter where I make my debut, I will give it my best," said Langerak who will face Bayern's star-studded attack led by Holland's Arjen Robben, France's Franck Ribery and Germany's Bastian Schweinsteiger.
"Besides, I have been working for weeks and months for this chance, I am ready."
The hosts desperately need a win to have a chance of retaining their title as Bayern are third in the league and 13 points behind Dortmund.
This is Langerak's big chance to impress after spending the last 25 games on the bench.
He will be facing Bayern's in-form Germany striker Mario Gomez, who has scored 28 goals in 32 matches for the Bavarian giants this season.