How do I add another language to my app's metadata?

When you create a new app, it is set to be available in all Amazon Appstore marketplaces by default. If desired (and especially if your APK supports localization), you can localize the store listing (the descriptions and image assets) of your app in multiple marketplaces to provide a better experience in those marketplaces.

During Step 3: Add Appstore Details of the app submission process, click “Add localization”.