Recently I noticed that the apps I installed from the Fedora Flatpak repo do not have their interfaces translated to my system language. When I search dash for the name of the apps they are translated.
When I install those same apps - Image Viewer (EoG) and Document Viewer (Evince) for instance - from Flathub they are fully translated.
I don’t know if this a missing feature from Fedora Flatpak repo, a missing runtime, or a bug.
I happen to know that this is a known issue. It’s on the Silverblue developer’s blocker list to solve before proposing Silverblue as the Fedora default desktop edition.