DaF; Deutsch als Zweitsprache; German as a second language; DaZ; German as a foreign language ; Unhöflichkeit; Impoliteness; Rudeness; Politeness (style of speech) ; E-Mail; Voice mail; Chat; Computer-mediated communication ; Bitte; Request ; Text linguistics, contrastive; Textlinguistik, kontrastive; Contrastive text linguistics ; German ; Japanese