Изменение кодировки Win1251 в UTF8 (необычный случай)

response := send('GET', x);

function send(method, url: string; postParams: string = ''; cookie: string = ''; showCookie: boolean = false; proxyType: string = ''; proxy: string = ''; proxyUser: string = ''; proxyPass: string = ''; files: string = ''; userAgent: string = ''; referer: string = ''): string;
var
  Header: TStringList;
  Contents: TStringList;
  httpsend: THTTPSend;
  ss: TStringStream;
  i, err: integer;
  s: string;
  FS: TFileStream;
  rev, bound: string;
  mas, mas2, p, v: array[0..500] of string;
const
  FIELD_MASK = #13#10 + '--%s' + #13#10 + 'Content-Disposition: form-data; name="%s"' + #13#10 + #13#10 + '%s';
begin
  randomize;
  Header := TStringList.Create;
  Contents := TStringList.Create;
  ss := TStringStream.Create('');
  httpsend := THTTPSend.Create;
  httpsend.UserAgent := userAgent;
  if referer <> '' then
    httpsend.Headers.Insert(0, 'referererer: ' + referer); //referererer
  httpsend.Cookies.Text := cookie;                //cookies
  if files <> '' then
  begin
    bound := IntToHex(Random(100000000), 8) + '_Synapse_boundary';
 
    s := '--' + bound + #13#10;
    i := 0;
    if pos('&', files) <> 0 then
    begin
      explode(mas, '&', files);
    end
    else
      mas[0] := files;
    while mas[i] <> '' do
    begin
      explode(mas2, ',', mas[i]);
 
            //s:=CRLF;
      s := s + 'content-disposition: form-data; name="' + mas2[0] + '";';
      s := s + ' filename="' + ExtractFileName(mas2[1]) + '"' + #13#10;
      s := s + 'Content-Type: ' + mas2[2] + #13#10 + #13#10;
            //showmessage(s);
      httpsend.Document.Write(Pointer(s)^, Length(s));
      if mas2[1] <> '' then
      begin
        FS := TFileStream.Create(mas2[1], fmOpenRead);
        FS.Position := 0;
        httpsend.Document.CopyFrom(FS, FS.Size);
        FS.Free;
      end;
      inc(i);
    end;
    explode(p, '&', postParams);
    i := 0;
    if pos('&', postParams) <> 0 then
    begin
      explode(p, '&', postParams);
    end
    else
      p[0] := postParams;
    while p[i] <> '' do
    begin
      explode(v, '=', p[i]);
      s := Format(FIELD_MASK, [bound, v[0], v[1]]);
      httpsend.Document.Write(Pointer(s)^, Length(s));
      inc(i);
    end;
    s := #13#10 + '--' + bound + '--' + #13#10;
    httpsend.Document.Write(Pointer(s)^, Length(s));
    httpsend.MimeType := 'multipart/form-data, boundary=' + bound;
  end
  else
  begin
    httpsend.MimeType := 'application/x-www-form-urlencoded;';
    if method = 'POST' then
    begin
      ss.WriteString(postParams);
      httpsend.Document.LoadFromStream(ss);
    end;
  end;
  httpsend.Protocol := '1.1';
     // httpsend.Sock.OnStatus := OnStatus;
  httpsend.Headers.AddStrings(Header);        //headers
  if proxyType = 'HTTP' then
  begin
    httpsend.ProxyHost := Copy(proxy, 1, Pos(':', proxy) - 1);
    httpsend.ProxyPort := Copy(proxy, Pos(':', proxy) + 1, Length(proxy));
  end
  else if proxyType = 'SOCKS 4' then
  begin
        //HTTPsend.Sock.SocksType:=
    httpsend.Sock.SocksResolver := false;
    httpsend.Sock.SocksIP := Copy(proxy, 1, Pos(':', proxy) - 1);
    httpsend.Sock.SocksPort := Copy(proxy, Pos(':', proxy) + 1, Length(proxy));
    httpsend.Sock.SocksUsername := proxyUser;
    httpsend.Sock.SocksPassword := proxyPass;
        //HTTPsend.Sock.SocksOpen;
  end
  else if proxyType = 'SOCKS 5' then
  begin
        //HTTP.Sock.SocksType := ST_Socks5 ;
    httpsend.Sock.SocksResolver := false;
    httpsend.Sock.SocksIP := Copy(proxy, 1, Pos(':', proxy) - 1);
    httpsend.Sock.SocksPort := Copy(proxy, Pos(':', proxy) + 1, Length(proxy));
    httpsend.Sock.SocksUsername := proxyUser;
    httpsend.Sock.SocksPassword := proxyPass;
        //HTTPsend.Sock.SocksOpen;
  end;
  if method = 'GET' then
  begin
    try
      httpsend.HTTPMethod('GET', url);
    except
       //on EidSocketError do
      on E: Exception do
        result := 'exception';
    end;
  end;
  if method = 'POST' then
  begin
    httpsend.HTTPMethod('POST', url);
  end;
  Contents.LoadFromStream(httpsend.Document);
  rev := Contents.Text;
  if pos('302', IntToStr(httpsend.ResultCode)) <> 0 then
  begin
    result := httpsend.Headers[FoundLocationStrNum('Location', httpsend.Headers)];
  end
  else if pos('500', IntToStr(httpsend.ResultCode)) <> 0 then
  begin
    result := '500' + httpsend.Headers.Text;
  end
  else if pos('404', IntToStr(httpsend.ResultCode)) <> 0 then
  begin
    result := '404';
  end
  else if pos('400', IntToStr(httpsend.ResultCode)) <> 0 then
  begin
    result := '400';
  end
  else if pos('307', IntToStr(httpsend.ResultCode)) <> 0 then
  begin
    result := httpsend.Headers[FoundLocationStrNum('Location', httpsend.Headers)];
  end
  else if pos('301', IntToStr(httpsend.ResultCode)) <> 0 then
  begin
    result := httpsend.Headers[FoundLocationStrNum('Location', httpsend.Headers)];
  end
  else
    result := rev;
  if showCookie = true then
    result := httpsend.Cookies.Text + '@@@' + result;
  httpsend.Free;
  Header.Free;
  Contents.Free;
  ss.Free;
 
  exit;
end;

а версия-то какая у вас?

  IdHTTP1.Request.Accept := 'application/json';
  IdHTTP1.Request.AcceptCharSet := 'UTF-8';
  s:=IdHTTP1.Get(URL);

Contents.LoadFromStream(httpsend.Document);

Contents.LoadFromStream(httpsend.Document, TEncoding.UTF8);

Memo1.Text := UTF8ToString(response);