I also found this: https://www.phrases.org.uk/meanings/double-dutch.html https://www.phrases.org.uk/meanings/double-dutch.html Which seems to suggest that "Dou

I also found this: https://www.phrases.org.uk/meanings/double-dutch.html https://www.phrases.org.uk/meanings/double-dutch.html Which seems to suggest that "Double Dutch" (and "High Dutch") actually refer to the German language.