Why does Mrs. Frank lapse into speaking German in the nightmare scene and in the scene where she catches Mr. Van Daan stealing the bread?

Act and scene, please?

act one, scene 4 and act two scene 3

From the text, we can infer that Mrs. Frank's conversation with her husband is meant for his ears only....speaking in German affords them some privacy.

In Act II, I believe Mrs. Frank's language change is a direct result of anger.