Loto, Praiwan. “The Honorific System in German as a Phenomenon of Courtesy: The Culturally Contrastive Analysis of Foreign Language Learning Exemplified through the Use of the Personal Pronouns Du and Sie by Thai German-learners at Chiang Mai University”. Journal of Letters 47, no. 3 (December 29, 2018): 339–378. accessed December 10, 2025. https://so03.tci-thaijo.org/index.php/jletters/article/view/158850.