Anyone with access to the app in Shopify admin can open it in the language saved in Settings.
The language is an app setting, not a per-user theme. If two people share the store, they share that choice until someone changes it.
One language setting
- Staff need permission to open Apps
- The interface language is in Settings
- Task history is the same for the store
- The published file is on the storefront, not inside a staff account
If a staff member cannot see the app, check their Shopify permissions before you reinstall.