You change the language of the WMS App in the settings of your iPhone or iPad. The app follows the language setting of the iOS device, not the user who logs in to the app.
If you change the language of the entire device under Settings → General → Language & Region, the WMS App also displays this language.
Set the language for the WMS App only
If employees work with different languages on one device, you can set the language for the WMS App only, without changing the language of the entire device:
Open the settings of your iOS device.
Search for the WMS App and tap it.
Select the language you want there.
Note: If the language you want does not appear in the selection, at least two languages must be added under Settings → General → Language & Region in the Preferred Languages section. If only one language is added there, iOS hides the selection. You can add more languages via Add Language.
You can find everything else about setting up the app in How can I set up the Pickware WMS App?