Franz thinks, "Will they make them sing in German, even the pigeons?" What could this mean?
(There could be more than one answer.)

Explanation

Language is inherent to culture and identity. The authority of human beings is restricted only to false boundaries that can be controlled. Nature and other things cannot be governed by some superficial laws of the wilful people. By taking the reference of making the pigeons learn German, the author is pointing to this very constraint.
(or)
This sentence could possibly mean that however hard the authorities try to embed German language in the culture of Alsace and Lorraine, the natural status of French, for them, will remain unchanged. French flows in the air and the entire place is imbued with its effect. Even though they train students in German, the basic mode of communication would remain unchanged like the cooing of the pigeons.
(Two model answers have been provided for students' reference. It is strongly recommended that students prepare the answer on their own.)