o google é nosso amigo!
<html>
<head>
<script type="text/javascript">
// IE default language for the browser
if (navigator.browserLanguage){language=navigator.browserLanguage}
// IE browser language set by the user
if (navigator.userLanguage){language=navigator.userLanguage}
// IE operating system language
if (navigator.systemLanguage){language=navigator.systemLanguage}
// Netscape language sniff
if (navigator.language){language=navigator.language}
// Turn all variants of "en-us", "en-au" etc into plain "en"
if (language.indexOf('-')==2) {language=language.substring(0,2);}
if (language=='da') {direct='http://www.yahoo.dk'}
else if (language=='sw') {direct='http://www.yahoo.se'}
else if (language=='en') {direct='http://www.yahoo.com'}
else {direct='http://www.echoecho.com'}
window.location.href=direct;
</script>
</head>
<body>
</body>
</html>
não testei mas deve funcionar