How to add localised raw app screenshots
You can add your localised raw app screens for each language within the screenshots section.
Open your project
In the top action bar click on App Screens
In the top right hand corner if you have multiple languages setup in your project, you will see a language drop down.
Select the language you'd like to upload your raw app screens to and drop the images into their relevant target/device frames.
Hit save
Note: If you do not upload localised app screens for each language you have setup, they will default to the app screens added in your 'default language'.

To view your project in each language, from the action bar, click on the language dropdown.
Note that any changes you make in the designer when viewing other languages, will pull across to the design in all other languages in your project as well.