How to change the Languages value shown under the Information section for my app in App Store?
You should use Xcode's localisation functionality to provide languages for your app.


  The list of languages displayed in the store under Languages is set in the app build.


Displaying on the Store in More Than One Language (Optional) - iTunes Connect Developer Guide

If you don't use Xcode's localisation, you'll have to set the languages manually by adding them to the CFBundleLocalizations array in your Info.plist.


  CFBundleLocalizations (Array - iOS, macOS) identifies the localizations handled manually by your app. If your executable is unbundled or does not use the existing bundle localization mechanism, you can include this key to specify the localizations your app does handle.


Core Foundation Keys - Information Property List Key Reference