> So no, you cannot "simply" use ToUpper() / ToLower(). They might work well enough of basic ASCII for languages like English, but they have a habit of making a mess out of everything else. You're supposed to use CultureInfo.TextInfo.ToUpperCase() and explicitly specify what locale the text is in so that it can use the right converter. Which is of course essentially impossible in general-purpose text fields.
Yes. Now try applying it to something like this very HN comment section, which is mixing words belonging to different cultures inside a single comment - and in some cases even inside the same word.
Sure, you can now do case conversion for a specific culture, but which one?
Have you ever read the documentation? https://learn.microsoft.com/en-us/dotnet/fundamentals/runtim...