Unable to view Chinese text in app

I have some notes in Simplenote that include Chinese text. These appear fine in the browser and mobile app but as □ in the flatpak app. Is there a way to enable support for this in the flatpak? I assume this would come in the form of bundling CJK fonts in some way.

Start by inspecting the Flatpak packaging configuration for the Simplenote app and how fonts are provided. Confirm the issue with notes containing Chinese text, then verify that the packaged app renders those characters instead of square glyphs.

Written by the indexing model from the issue text.