Its clear that "Ñîáëþäåíèå ïðàâ äåòåé â äåòñêèõ äîìàõ Êûðãûçñêîé Ðåñïóáëèêè"
is iso-8859-1-encoded string. And you should convert it to windows-1251, but you are doing the opposite.
Just switch cp1251
and iso8859
everywhere inside button1_Click
and you'll see correct result.
Maybe you want to use data as unicode, then convert it like this
Encoding utf8 = Encoding.GetEncoding("utf-8");
Encoding iso8859 = Encoding.GetEncoding("iso-8859-1");
Encoding cp1251 = Encoding.GetEncoding("windows-1251");
private void button1_Click(object sender, EventArgs e)
{
byte[] bytes = iso8859.GetBytes("Ñîáëþäåíèå ïðàâ äåòåé â äåòñêèõ äîìàõ Êûðãûçñêîé Ðåñïóáëèêè"); // get bytes in source encoding
// but they are actually cp1251 so...
string utf8string = utf8.GetString(Encoding.Convert(cp1251, utf8, bytes)); // convert them from cp1251 to utf8
label1.Text = utf8string;
}