Repository: flutter
Issue: Platform.localname returns "de_DE" instead of "de_CH" for Swiss German under Windows (iOS and MacOS work correctly)
Labels: engine,a: internationalization,platform-windows,has reproducible steps,P2,found in release: 3.16,found in release: 3.20,team-windows,triaged-windows

### Steps to reproduce

1. Set regional settings to "Swiss German" under Windows 11 (see screenshot)
2. Create a new flutter project
3. call print(Platform.localeName);    

Dart itself is probably correct. Flutter supposedly has a seaparate implementation for the locale, which has this issue. See comment: https://github.com/dart-lang/sdk/issues/54904


### Expected results

Platform.localname and findSystemLocale() should return the correct value "de_CH" for Swiss German under Windows


### Actual results

Today Platform.localname returns the wrong code "de_DE" instead of "de_CH" for Swiss German under Windows. The effect is that the wrong currency "EUR" instead of "CHF" is used under Windows.
On macOS and iOS, however, the code is returned correctly!

### Code sample

<details open><summary>Code sample</summary>

```dart
import 'dart:io';

void main() {
// returns "de_DE" instead of "de_CH"
  print(Platform.localeName);  
}
```

</details>


### Screenshots or Video

<details open>
Regional settings with "Swiss German" under Windows 11:

![image](https://github.com/flutter/flutter/assets/97222956/60615c82-5040-41a2-a38e-acbc1e13877a)

</details>


### Logs

<details open><summary>Logs</summary>

```console
[Paste your logs here]
```

</details>


### Flutter Doctor output

<details open><summary>Doctor output</summary>

```console
flutter doctor -v
[√] Flutter (Channel stable, 3.16.9, on Microsoft Windows [Version 10.0.22621.3007], locale de-CH)
    • Flutter version 3.16.9 on channel stable at C:\develop\flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 41456452f2 (3 weeks ago), 2024-01-25 10:06:23 -0800
    • Engine revision f40e976bed
    • Dart version 3.2.6
    • DevTools version 2.28.5

[√] Windows Version (Installed version of Windows is version 10 or higher)

[√] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
    • Android SDK at C:\Users\st-ro\AppData\Local\Android\sdk
    • Platform android-34, build-tools 34.0.0
    • Java binary at: C:\Program Files\Android\Android Studio\jbr\bin\java
    • Java version OpenJDK Runtime Environment (build 17.0.7+0-b2043.56-10550314)
    • All Android licenses accepted.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe

[√] Visual Studio - develop Windows apps (Visual Studio Community 2022 17.8.5)
    • Visual Studio at C:\Program Files\Microsoft Visual Studio\2022\Community
    • Visual Studio Community 2022 version 17.8.34511.84
    • Windows 10 SDK version 10.0.22621.0

[√] Android Studio (version 2023.1)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin can be installed from:
       https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
       https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 17.0.7+0-b2043.56-10550314)

[√] VS Code (version 1.86.0)
    • VS Code at C:\Users\st-ro\AppData\Local\Programs\Microsoft VS Code
    • Flutter extension version 3.50.0

[√] Connected device (3 available)
    • Windows (desktop) • windows • windows-x64    • Microsoft Windows [Version 10.0.22621.3007]
    • Chrome (web)      • chrome  • web-javascript • Google Chrome 121.0.6167.161
    • Edge (web)        • edge    • web-javascript • Microsoft Edge 121.0.2277.112

[√] Network resources
    • All expected network resources are available.

• No issues found!

```

</details>