Hello,
>>However, the languages management available on my App is not working correctly (there is no problem running the App in the Visual Studio), and various labels and images are not being displayed while running the Publicated App.
This reason for this issue is that you generated the App bundle for your app. When using the App Bundle, it will cut your application into different parts to optimize the download and installation process. Only the language resources that match the current language and culture of the device will be installed. This optimized installation feature is automatically enabled when your application's .appxbundle is generated during packaging.
That’s why the appxupload package works well because it’s not App bundle. If you still want to use the App bundle, you will need to keep all the language resources in the package. Please create a configuration file for the app package. It will specify that certain resources are required during installation (including language resources).
There is more information from the "Deployment Considerations" section of this document: Make your app localizable
For more information, you could refer to this question: Localization issues when using App Bundle in UWP.