Export JSON to CSV or Excel with UTF-8 (e.g. Greek) encoding using JavaScript

I am trying to export and download a JSON object to CSV file and I have problem with Greek characters. My code works; it is not perfect, but it works.

The problem is that Greek characters looks like junk.

Here is my existing code:

function downloadJsonToCsv(jsonObject) {
    var array = typeof jsonObject != "object" ? JSON.parse(jsonObject) : jsonObject;

    if (array == null) {
        return; // No data found on the jsonObject
    }

    var str = "";

    for (var i = 0; i < array.length; i++) {
        var line = "";

        for (var index in array[i]) {
            line += array[i][index] + ";"; // Set delimiter
        }

        // Here is an example where you would wrap the values in double quotes
        // for (var index in array[i]) {
        //    line += '"' + array[i][index] + '",';
        // }

        line.slice(0,line.Length-1); 

        str += line + "\r\n";
    }

    window.open("data:text/csv;charset=utf-8," + encodeURI(str));
}

I have two questions.

1. How can export this CSV file with correct Greek chars?
2. How can I export this data in Excel format and not in CSV format?