Using modern slang in subtitles would break the immersion.
David J. Peterson developed full languages for the show, including: The language of nobility and dragons. Dothraki: The harsh, guttural tongue of the horse lords. Game of Thrones (2011) Legendas
Translators had to decide whether to translate these into the target language (e.g., Portuguese) or maintain a secondary layer of subtitles. Often, the English subtitles for these languages were translated literally, but preserving the "feel" of the invented syntax was a major hurdle. 2. Archaisms and Formal Tone Using modern slang in subtitles would break the immersion
