Description

In the new Windows 11 based themes, text is set to Justify Alignment by default. This default does not make sense and has never been the case in WPF and is not the default in UWP. In English it should be left aligned.

Default:

Explicitly setting it to Left:

Reproduction Steps

Create a new WPF project and add a TextBox to the UI, add some text to it. Enable fluent themes in the project as described here: https://github.com/dotnet/core/blob/main/release-notes/9.0/preview/preview4/wpf.md#support-for-windows-11-theming.
You will see that the text is using Justify, even though it says it is using left alignment in the properties UI in Visual Studio.

Expected behavior

Text is left aligned or aligned according to the default for the language.

Actual behavior

Text is Justify aligned by default in English, when it should be left aligned.

Regression?

Yes, doesn't happen in .NET 8 or with the old themes.

Known Workarounds

Excplicitly set the text alignment to Left.

Impact

Looks strange and makes text harder to read.

Configuration

• .NET 9
• Windows 11 23H2 Build 22631.4602
• x64
• I am not sure if it is specific to this configuration.

Other information

No response