你可以创建一个自定义的Slider，它接受一个值转换器：

SliderEx.cs

public class SliderEx : Slider
{
    public IValueConverter? ValueConverter { get; set; }

    protected override void OnApplyTemplate()
    {
        base.OnApplyTemplate();
        this.LayoutUpdated += Slider_LayoutUpdated;
    }

    private void Slider_LayoutUpdated(object? sender, object e)
    {
        if (VisualTreeHelper
            .GetOpenPopupsForXamlRoot(this.XamlRoot)
            .FirstOrDefault() is not Popup popup ||
            popup.Child.FindDescendant<TextBlock>() is not TextBlock popupTextBlock)
        {
            return;
        }

        popupTextBlock.SetBinding(
            TextBlock.TextProperty,
            new Binding
            {
                Source = this,
                Path = new PropertyPath(nameof(this.Value)),
                Mode = BindingMode.OneWay,
                Converter = this.ValueConverter,
            });

        this.LayoutUpdated -= Slider_LayoutUpdated;
    }
}

ValueToSpeedConverter.cs

public class ValueToSpeedConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, string language)
    {
        return (double)value switch
        {
            >= 0 and < 20 => "Slow",
            >= 20 and < 30 => "Medium",
            >= 30 => "Fast",
            _ => $"{value}?",
        };
    }

    public object ConvertBack(object value, Type targetType, object parameter, string language)
    {
        throw new NotImplementedException();
    }
}

然后像这样使用它：

<StackPanel>
    <StackPanel.Resources>
        <local:ValueToSpeedConverter x:Key="ValueToSpeedConverter" />
    </StackPanel.Resources>

    <local:SliderEx
        x:Name="SliderControl"
        ValueConverter="{StaticResource ValueToSpeedConverter}"/>
</StackPanel>