Change encoding automatically to UTF-8 in CSV

Question

On my web-site there is possibility to export files in csv format. This export is implemented through button and its settings:

var button = $('<a/>', {
        style:'display:none',
        href:'data:application/octet-stream;base64,' + btoa(unescape(encodeURIComponent(string))),
        download: fileName
      });

Then I just trigger click and file downloads.

When I open it in google.docs everything is fine with encoding (file consists German symbols äüö), but when I open it in Excel, symbols are wrong, so I need to set file encoding to UTF-8 to see them.

But customer wants to click on file and then file is opened in excel without further import steps with encoding. Is it possible?