I in fact can assume it. If the assumption is wrong then that's someone else's problem. 15 years ago I wrote a bunch of code using uchardet to detect encodings

I in fact can assume it. If the assumption is wrong then that's someone else's problem. 15 years ago I wrote a bunch of code using uchardet to detect encodings and it was a pretty useful feature at the time. In the last decade everything I've touched has required UTF-8 unless it's been interoperating with a specific legacy system which has some other fixed charset, and it's never been an issue.