If you're using German umlauts, Scandinavian vowels, or non-European alphabets, you need to use UTF-8 encoding for your files. There are two ways of doing this.
1. Make sure your HTML page where your charts are defined, is UTF-8. The file itself and if applicable its database content must be encoded as UTF-8. Additionally, either the
content-type HTTP header or the corresponding meta tag must reflect this:
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
2. If you do not have access to change your whole HTML file, you can define your charts in a separate JS file that has UTF-8 encoding.
<script src="/charts.js" charset="UTF-8"></script>