How do I get a html post request to use a specific charset? - html

Question

I am trying to post a form using an encoding that was previously chosen by the recipient.
The problem I am facing is that I can't seem to get the encoding of the swedish characters åäö to be translated correctly. Consider the following form:
<form accept-charset="ISO-8859-1" action="http://httpbin.org/post" method="post" id="aForm">
<input type="hidden" name="hej" value="köttfärssås"/>
<input type="submit"/>
</form>
Posting this using Chrome gives me the following result:
{
"args": {},
"data": "",
"files": {},
"form": {
"hej": "k\ufffdttf\ufffdrss\ufffds"
},
"headers": {
"Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8",
"Accept-Encoding": "gzip, deflate",
"Accept-Language": "sv-SE,sv;q=0.8,en-US;q=0.6,en;q=0.4",
"Cache-Control": "max-age=0",
"Content-Length": "21",
"Content-Type": "application/x-www-form-urlencoded",
"Host": "httpbin.org",
"Origin": "null",
"User-Agent": "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/40.0.2214.93 Safari/537.36"
},
"json": null,
"origin": "85.119.130.112",
"url": "http://httpbin.org/post"
}
Not only are the åäö characters jumbled, there are no headers here showing which encoding is being used. What am I missing here?
I have also tried using <meta charset="ISO-8859-1"> and <meta http-equiv="Content-Type" content="text/html;charset=ISO-8859-1">, but with no success.
So, how do I force the form to use the encoding of my choice?