(old) method for adding languages to highlight.js on Discourse

I created new syntax highlighting for Jai: GitHub - Jai-Community/discourse-highlightjs-jai: Discourse theme component to highlight Jai syntax

However, when I install it and enter the theme preview mode, and then create a new topic and add some code, like this:

```jai
#run {}
```

… it does detect the language (see the class attribute), but it does not parse anything:

<pre><code class="lang-jai hljs">#run {}
</code></pre>

whereas running the same language definition with a local setup does highlight jai syntax successfully:

Try yourself by opening _dev/test-syntax-highlight.html in your browser.

Ideas?