[Bug] TextBlock Inlines (Bold/Italic) not working with Chinese characters

[LITTOMA]

Describe the bug

When using Avalonia TextBlock with Inlines (Bold, Italic, or Span with FontWeight/FontStyle), the special text formatting (bold/italic) doesn't work for Chinese characters. The Chinese text is displayed as normal text without any style changes.

To Reproduce

1. Create a TextBlock control
2. Add Inlines with Bold or Italic formatting for Chinese text
3. Example code & output:

public partial class MainView : UserControl
{
    public MainView()
    {
        InitializeComponent();
        InitInlineTextBlock();
        CreateFromCode();
    }

    private void CreateFromCode()
    {
        var _contentPanel = new StackPanel();
        var textBlock = new TextBlock
        {
            TextWrapping = TextWrapping.Wrap,
            FontSize = 16,
            HorizontalAlignment = Avalonia.Layout.HorizontalAlignment.Center,
            VerticalAlignment = Avalonia.Layout.VerticalAlignment.Center
        };
        textBlock.Inlines.Add(new Run("这是"));
        textBlock.Inlines.Add(new Bold { Inlines = { new Run("一个") } });
        textBlock.Inlines.Add(new Run("文本，由"));
        textBlock.Inlines.Add(new Italic { Inlines = { new Run("代码") } });
        textBlock.Inlines.Add(new Run("创建"));

        _contentPanel.Children.Add(textBlock);
        container.Children.Add(_contentPanel);
    }

    private void InitInlineTextBlock()
    {
        var bold = new Bold
        {
            Inlines =
            {
                new Run("一个")
            }
        };
        var italic = new Italic
        {
            Inlines =
            {
                new Run("代码")
            }
        };

        codeBehindTextBlock.Inlines.Add(new Run("这是"));
        codeBehindTextBlock.Inlines.Add(bold);
        codeBehindTextBlock.Inlines.Add(new Run("文本，由"));
        codeBehindTextBlock.Inlines.Add(italic);
        codeBehindTextBlock.Inlines.Add(new Run("更新"));
    }
}

<UserControl
    x:Class="AvaloniaTextBlockInlines.Views.MainView"
    xmlns="https://github.com/avaloniaui"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:vm="clr-namespace:AvaloniaTextBlockInlines.ViewModels"
    d:DesignHeight="450"
    d:DesignWidth="800"
    x:DataType="vm:MainViewModel"
    mc:Ignorable="d">

    <StackPanel Name="container" Orientation="Vertical">
        <TextBlock HorizontalAlignment="Center" VerticalAlignment="Center">
            这是一个<Bold>文本</Bold>
            ，由<Italic>叉啊姆鲁</Italic>
            创建</TextBlock>
        <TextBlock HorizontalAlignment="Center" VerticalAlignment="Center">
            This <Bold>English</Bold>
            text is created by<Italic>XAML</Italic>
        </TextBlock>
        <TextBlock
            Name="codeBehindTextBlock"
            HorizontalAlignment="Center"
            VerticalAlignment="Center" />
    </StackPanel>
</UserControl>

Expected behavior

Chinese characters should be displayed with bold or italic formatting, just like Latin characters do.

Avalonia version

11.2.0

OS

Windows

Additional context

No response

[NLick47]

Setting the font can solve the issue. Refer to https://github.com/irihitech/Semi.Avalonia/blob/main/src/Semi.Avalonia/Tokens/Variables.axaml#L64

[Gillibald]

Yes. The fallback algorithm does not make sure the weight and style are matching. The system font manager yields the first font that holds the requested character. It might be possible this issue can't be solved. This is an issue with the system font manager.

[LITTOMA]

When setting FontWeight and FontStyle on a TextBlock, Chinese text can be properly bolded and italicized. Why does this happen? Does TextBlock use software simulation to render these two special styles?

[Gillibald]

When setting FontWeight and FontStyle on a TextBlock, Chinese text can be properly bolded and italicized. Why does this happen? Does TextBlock use software simulation to render these two special styles?

Yes