How to convert ISO-8859-1 charset to normal string

I have a asp.net application and I uses ISO-8859-1 charset. But It is not OK. In the postback, I got ISO-8859-1 keycode. But the applicati开发者_开发百科on response next time, it is display like this. How can convert to normal fonts.

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 Encoding encoding = Encoding.GetEncoding("ISO-8859-1");
 var normalText= HttpUtility.UrlDecode(encodedText);