Fixing the “resource not found” warning when creating app packages for Windows 10 UWP applications

When developing XAML applications for Windows 10 UWP, you might get the following error message when creating app-packages for your app:

MakePRI: warning 0xdef00522: Resources found for language(s)
'en-us,de-de,es-es,fr-fr,it-it,ja-jp,ko-kr,pt-br,ru-ru,uk-ua,zh-cn,zh-tw'
but no resources found for default language(s): 'fi'. Change the default
language or qualify resources with the default language.

This error message came up when creating app packages (Visual Studio's command Project/Store/Create App Package) for an application that had its default language set to "fi" (Finnish).

To fix the problem, simply change the language to one of those mentioned in the list, such as "en-us".