What i mostly do, is represent the same page with an error message above, or as popup. The form is filled again with the values of the just submitted form.
Then the user doensn't even need the back-button.
Or use JavaScript for simple (front-end) form validation.
But anyway, i don't think it has anything to do with the UTF 8 chars.
"We all agree on the necessity of compromise. We just can't agree on when it's necessary to compromise." - Larry Wall.