If you are in Standard-Configuration and edit the error messages (404 x 4) and use accentuated, chinese, etc characters, go to Admin-Email Queue, click on preview and you get some gremlins...

Â

Error 404 - Mistyped URL

Â

对不起, 此网页不存在.

Â

Nous sommes désolés, il semble que la page demandée n'existe plus.

If it happens only editin 404 error message, then I have no clue

if it happens all around the website, then you need to change your database collation to utf8

viewtopic.php?f=7&t=691

DB is in utf8. You only see the gremlins when you click the preview button in the CMS.
The messages on the site and email are ok

Now I get it. You probably use chrome. Chrome for some reason don't get encoding when it is in email format. Preview shows exactly the same html as it would be send to email client. And chrome does not understand that. The email itself should be fine if it is fine using different browser. Is that your problem or you experience something else?

It is safari, wait I will tests all others.

The html code you get in the popup window is pure text, no encoding, no heading, nothing.

<p>Â </p>
<p><b>Error 404 - Broken Link</b></p>
<p>Â </p>
<p>对不起, 此网页不存在.</p>
<p>Â </p>
<p>Nous sommes désolés, il semble que la page demandée n'existe plus.</p>
<p>Â </p>

In safari you must go to ~Display-Encoding and choose UTF8 to make it appears correctly.
I think it is normal, if you do not define an encoding, it must show it like that.

These 'gremlins' are also valid characters (© ½ œ...) that one could have typed, so it must show them as is.