Android supports multiple application resource locales. Default strings are in values directory, other languages use values-XX directories. Can I set up Android Studio project to treat strings.xml in values directory (without language specification) as non-English strings (e. g. German)? I am 100% sure that all users know German.
Android makes no assumption about what language the strings are in res/values/. It is simply the default set of strings to use, for cases where you do not provide translations for some specific language.
If you want to use German strings in res/values/, you are welcome to do so. In that case, your English translations would go into res/values-en/ or a similar directory, should you someday elect to provide such translations.