in fact i have made one, if you think useful you can add this feature to new jedit versions. it find text like "content="text/html; charset=xxxxxx"" at the begin of the html.

[code]
BufferIORequest.java
    /**
     * Tries to detect if the stream is gzipped, and if it has an encoding
     * specified with an XML PI.
     */
    private Reader autodetect(InputStream in) throws IOException {
        in = new BufferedInputStream(in);

        String encoding = buffer.getStringProperty(Buffer.ENCODING);
        if (!in.markSupported())
            Log.log(Log.WARNING, this, "Mark not supported: " + in);
        else if (buffer.getBooleanProperty(Buffer.ENCODING_AUTODETECT)) {
            
            {// neoe add: detect html's encoding
                String enc = getHtmlEncoding(in);
                if (enc != null && MiscUtilities.isSupportedEncoding(enc)) {
                    buffer.setProperty(Buffer.ENCODING, enc);
                    return new InputStreamReader(in, enc);
                }
            }
	....
	(original lines)

/**add by neoedmund*/	
private String getHtmlEncoding(InputStream in) throws IOException {
        String enc = null;
        String key = "charset=";        
        int bufSize=1000;
        byte[] buf = new byte[bufSize];
        in.mark(bufSize);
        int len;
        if  ((len = in.read(buf,0,bufSize)) >0) {
            String line=new String(buf,0,len);    
            int p1 = line.indexOf(key);
            if (p1 >= 0) {
                int p2 = p1 + key.length();
                p1 += key.length();
                if (line.charAt(p1) == '\'' || line.charAt(p1) == '"') {
                    p1++;
                }
                while (p2 < line.length()
                        && "'\" >;,.".indexOf(line.charAt(p2)) < 0) {
                    p2++;
                }
                if (p2 <= line.length()) {
                    enc = line.substring(p1, p2);
                }
            }
        }
        in.reset();        
        return enc;
    }
[/code]