The Book Thief
Why do you think the author included entries from the German dictionary?
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I believe the author included these entries in order to provide further realism to the story. The Duden dictionary is a "German reference dictionary, first published in 1880, that is generally considered to be the standard of German spelling and pronunciation."
http://www.gradesaver.com/the-book-thief/study-guide/glossary-of-terms/