I have a Xamarin.IOS application and try to localize some images. As a guideline I took this article: https://developer.xamarin.com/guides/ios/advanced_topics/localization_and_
So as I pointed out in the comments, you should put fallback resources into the Base.lproj folder.
As for your issue with InfoPlist.strings, keep in mind that they are applied only for strings in your Info.plist, so that is when you are asking for permissions etc. This could look as follows for da.lproj:
"NSLocationWhenInUseUsageDescription" = "Vil du tillade App'en til at bruge din lokation?";
"NSCalendarsUsageDescription" = "Ost";
and so on.
As for other strings, such as OK, Cancel and other buttons, you will need to add a Localizable.strings file for each folder with contents like:
"Back" = "Tilbage";
"Done" = "Færdig";
"Cancel" = "Anuller";