The article "Change your Apple ID country or region" describes how to change your country setting on everything using your Apple ID, and the requirements and results of doing this --> Change your Apple ID country or region - Apple Support
"Redownload your apps, music, movies, TV shows, and books on any devices that you might use to play or read them in the future. Some types of content might not be available in your new country or region. (Learn what types of content and services are available in your new country or region. - Availability of Apple Media Services - Apple Support )"
I don't know how to check for app availability by region other than finding the URL for the app on the App Store and then forcing it to use a different country reference. E.g.,
My default in the USA: https://apps.apple.com/us/app/maps-me-offline-maps-gps-nav/id510623322
German version: https://apps.apple.com/de/app/maps-me-offline-maps-gps-nav/id510623322