I have been using "Summarize in Document Language" for a while and it has always detected the right Document Language, except today when I was reading this article https://www.wired.com/story/elon-musk-twitter-rate-limits-extremely-hardcore/
Somehow it got summarized in Spanish (which is a language I have never summarized in before, so not my default language or an old preset). Original language should have been English.
Let me know if you need more details, thanks!