Unpackage apps ToggleSwitch's On/Off Content can't change by PrimaryLanguageOverride

### Describe the bug

As the title says. In unpackage apps, I try to set PrimaryLanguageOverride. Then the language in the application has changed, but the On/Off Content of ToggleSwitch is still the system language, not the corresponding language of PrimaryLanguageOverride. This will not happen in Package apps.

### Steps to reproduce the bug

1. Set your system language to non-English. Such as Chinese, French, Japanese, etc.
2. In App.xaml.cs, `Microsoft.Windows.Globalization.ApplicationLanguages.PrimaryLanguageOverride = "en-us"`
3. Run application as Unpackage

### Expected behavior

You will see, ToggleSwitch's On/Off Content text will be your system language.If you run application as Package, the text will be displayed correctly in English.

### Screenshots

Unpackage:


Package:


### NuGet package version

WinUI 3 - Windows App SDK 1.6.6: 1.6.250228001

### Windows version

Windows 11 (23H2): Build 22631

### Additional context

_No response_

Reproduce the issue from App.xaml.cs using PrimaryLanguageOverride with a non-English system language, comparing packaged and unpackaged runs on Windows App SDK 1.6.6. Start by tracing ToggleSwitch's On/Off content localization and the package-mode difference. Done means the unpackaged ToggleSwitch displays the override language consistently with the packaged app.

Written by the indexing model from the issue text.