Japanese not shown correctly in preview image

This is a preview (from Twitter) for a cast I just posted. The squares on the left should all be Japanese.

szd-WOyU

The cast:

https://asciinema.org/a/3G322ywudzGgKAvTUtYfBEYj0

The cast itself shows Japanese just fine, I guess whatever is generating the thumbnail image doesn’t have the right fonts installed. Any chance of getting this fixed?

The image for Twitter is a PNG generated from SVG. For this conversion we use rsvg tool. It could be the OS (Alpine) this is running on doesn’t have the proper fonts installed…

Do you know what font package on Linux could be installed to fix that?

There should be a Japanese fonts or CJK font package, many distros package the Google Noto fonts for that purpose (though the CJK pack may be separate due to size). No idea what it’s called on Alpine.