App shows different language than device is set to

This may be a newbie question, but the following seems very strange to me.

My devices (iPhone, iPad) use Dutch ("nl") as language (Configured with Settings / General / Language & Region / iPhone Language). And similarly Netherlands ("NL") as region.

But if I run the following program:

import SwiftUI

struct ContentView: View {
    var body: some View {
        Text(Locale.current.description)
        Text(Locale.current.languageCode!)
    }
}

I get the following output:

en_NL (current)

en

I checked the run settings in Xcode. App Language is set to System Language, and App Region is set to System Region.

It seems to me that I should see

nl_NL (current)

nl

Am I right? Do I misunderstand Locale? Am I missing something else? Thanks!