ApplicationLanguages.PrimaryLanguageOverride cannot be unset

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Describe the bug

The Microsoft.Windows.Globalization.ApplicationLanguages.PrimaryLanguageOverride property by default returns an empty string (if the app has not set a language override before). However, once a language override was set, it can no longer be unset to remove the override. Setting PrimaryLanguageOverride = "" or PrimaryLanguageOverride = null will both throw an exception.

In comparison, Windows.Globalization.ApplicationLanguages.PrimaryLanguageOverride does allow setting an empty string, which will clear the previous override. However setting Windows.Globalization.ApplicationLanguages.PrimaryLanguageOverride will not clear the Microsoft.Windows.Globalization.ApplicationLanguages.PrimaryLanguageOverride property for packaged apps, so it is only an incomplete workaround.

The following check must be changed to also allow an empty string:

WindowsAppSDK/dev/MRTCore/mrt/Microsoft.Windows.ApplicationModel.Resources/src/ApplicationLanguages.cpp

Line 44 in 3d8013b

bool isValidLanguageTag = IsWellFormedTag(language.c_str());

Steps to reproduce the bug

1. Set the override to some language, e.g. Microsoft.Windows.Globalization.ApplicationLanguages.PrimaryLanguageOverride = "fr-FR";
2. Try to unset the override, e.g. Microsoft.Windows.Globalization.ApplicationLanguages.PrimaryLanguageOverride = "";

Expected behavior

No exception is thrown when an empty string is set, and the language override will be reset.

Screenshots

No response

NuGet package version

Windows App SDK 1.7.1: 1.7.250401001

Packaging type

Packaged (MSIX)

Windows version

Windows 11 version 24H2 (22621, October 2024 Update)

IDE

Visual Studio 2022

Additional context

No response