C# Convert string from UTF-8 to ISO-8859-1 (Latin1) H

Use Encoding.Convert to adjust the byte array before attempting to decode it into your destination encoding.

Encoding iso = Encoding.GetEncoding("ISO-8859-1");
Encoding utf8 = Encoding.UTF8;
byte[] utfBytes = utf8.GetBytes(Message);
byte[] isoBytes = Encoding.Convert(utf8, iso, utfBytes);
string msg = iso.GetString(isoBytes);

I think your problem is that you assume that the bytes that represent the utf8 string will result in the same string when interpreted as something else (iso-8859-1). And that is simply just not the case. I recommend that you read this excellent article by Joel spolsky.

Try this:

Encoding iso = Encoding.GetEncoding("ISO-8859-1");
Encoding utf8 = Encoding.UTF8;
byte[] utfBytes = utf8.GetBytes(Message);
byte[] isoBytes = Encoding.Convert(utf8,iso,utfBytes);
string msg = iso.GetString(isoBytes);