macOS lets users configure a preferred language via "Regional Settings -> Language & Region -> Preferred languages". macOS then uses the preferred language to localize system menus and dialogs for localizable application. To mark your Mac application as localizable, add the locales you plan to support localization for to the "Info.plist" file of your application's executable project. For example:

A list with the supported by macOS languages for localization is available at CFBundleLocalizations Apple Documentation topic.

When you add these locales to your application's "Info.plist" file in Visual Studio for Mac and you run your application on a Mac configured with a "German" preferred language, you will get the following Save File dialog: