A german forum pm'd login credentials for host account. Password includes english alpha/numeric characters, and a '?'. If I type the password manually, or copy it from Notepad, it fails. If I copy it from pm, it works. Apparently the '?' is actually a diacritic letter, which is not displayed correctly in pm because this forum is not running german utf-8, but it copies correctly from pm. How does that work?
The ? indicates one of two things: either a malformed character or a character glyph in a font you don't have installed.
As for 'German UTF-8', this forum is installed with UTF-8 just fine and has been for years. It doesn't require you viewing it in the 'correct' language pack for it to be a thing.
As for why it fails if you type it directly, you're probably typing the wrong character (a literal ? is not the right one) and copying it to Notepad will shift it to a different encoding, probably Win-1252 (unless you've told Notepad to not treat it as such). If in doubt, save the PM page as is and examine the individual bytes with a hex editor to see what it is.
If the browser is not able to display the character correctly, then I shouldn't be able to copy it from the pm, because the browser has substituted a ? for that character. I can see the umlauts in Götterdämmerung, copy it to Notepad, and it displays them correctly. ???
Just because the browser can't display it for some reason, doesn't mean it isn't aware of what the bytes are.