Text shows as boxes?
Every script is drawn with your system fonts. If a script has no font, install one.
Why it happens
MarkCluster doesn't bundle fonts. Arabic, Hebrew, Indic, Thai, Myanmar and Ethiopic text uses fonts that Windows and macOS normally include. Some Linux systems don't have them.
If no font for your display language is found, MarkCluster shows English instead of empty boxes and tells you which font to install. The language list marks such languages with ⚠.
Fix it on Linux
$ sudo apt install fonts-noto-core fonts-noto-cjk
Restart MarkCluster afterwards.