For pages already specified (either by HTTP header, or by meta tag), to have a Content-Type with a UTF-8 charset... is there a benefit of adding
If the page is already interpreted by the browser as being UTF-8, setting
accept-charset="utf-8" does nothing.
If you set the encoding of the page to UTF-8 in a
<meta> and/or HTTP header, it will be interpreted as UTF-8, unless the user deliberately goes to the View->Encoding menu and selects a different encoding, overriding the one you specified.
In that case,
accept-encoding would have the effect of setting the submission encoding back to UTF-8 in the face of the user messing about with the page encoding. However, this still won't work in IE, due the previous problems discussed with
accept-encoding in that browser.
So it's IMO doubtful whether it's worth including
accept-charset to fix the case where a non-IE user has deliberately sabotaged the page encoding (possibly messing up more on your page than just the form).
Personally, I don't bother.