To add files in an Android apk, you need to put them in an assets folder and then they are in an "assets" folder in the APK.
Log4j 2 needs to find it there when it exists (not the case now).
Also would it be possible to load the xml configuration file from the application data ( https://developer.android.com/guide/topics/data/data-storage.html ) ?
UPDATE: The file is loaded correctly, but it's processing is not done fully. See comments below.