Congratulations to nostr:npub1cppnptddm9ggcxk3cmk7ptk4my32xetsyxfhugz44qxpk2r9enmszgyqlx for solving the puzzle! Here is the answer:

A: John used the differences in the alphabets to identify the languages; Cyrillic for Russian, French with accented letters, and German with words containing umlauts or ß.

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