which languages did they speak?
German, Polish, Danish, Dutch and Frisian etc
German Empire
German as their first language. The only minority language with a significant number of speakers (5.4%) was Polish (a figure that rises to over 6% when including the related Kashubian and Masurian languages).
paragraph 231 of the versailles treaty dealt with It was the opening article of the reparations section of the Treaty of Versailles, which ended the First World War between the German Empire and the Allied and Associated Powers. who wrote it? Norman Davis and John Foster Dulles which countries were part of this empire? The empire  consisted of 26 states, most of them ruled by royal families.
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German Empire [SEP] Language
About 92% of the population spoke German as their first language. The only minority language with a significant number of speakers (5.4%) was Polish (a figure that rises to over 6% when including the related Kashubian and Masurian languages). The non-German Germanic languages (0.5%), like Danish, Dutch and Frisian, were located in the north and northwest of the empire, near the borders with Denmark, the Netherlands, Belgium, and Luxembourg. Low German was spoken throughout northern Germany and, though linguistically as distinct from High German ("Hochdeutsch") as from Dutch and English, is considered "German", hence also its name. Danish and Frisian were spoken predominantly in the north of the Prussian province of Schleswig-Holstein and Dutch in the western border areas of Prussia (Hanover, Westphalia, and the Rhine Province).