A button remaining clickable without a connection does not make an experience offline. Ask whether someone can finish the main job: read data, look something up, record progress and reopen their work.
Start with a dependency map. For each action, identify where its data lives and which step needs a network. If a definition is on the device but pronunciation has not been downloaded, explain that instead of making the entire screen wait.
Distinguish bundled content from optional downloads. A downloadable pack needs not-downloaded, downloading, ready and failed states. An interrupted, incomplete file must not be treated as usable data.
Make saving progress or notes understandable. “Saved on this device” is different from “Synced”. If multiple devices are supported, decide how conflicting edits are handled; the most recent arrival is not automatically what the person intended to keep.
A useful check is opening the app offline for the first time, then repeating after downloading content. Next, interrupt a connection during an action and restart the app. Look for places where the interface promises more than the available data permits.
Offline has limits too: device storage, data versions and backups still matter. Explain what works immediately, what needs downloading first and what needs a connection. People should not have to understand the architecture to understand the tool.