In my manifest file I have currently just one language setting.
Resource Language="en-us"
I want to make the app to work in all english stores (e.g. UK), which parameter should I choose? Also, my App has multiple languages supported natively, so I need above codes for spanish, french, german and dutch languages, all regions, where can I find the corresponding codes?
You can query the language tags in the list of languages supported by the Windows Store.
Just specify the list of your app's supported language in the Resources element inside your app's manifest file.
Additionally, here is an sample app for manage languages and region setting.
For more details, you may refer to Specify the supported languages in the app's manifest.