gistfile1.xml

<Window x:Class="FontFallbackTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:FontFallbackTest="clr-namespace:FontFallbackTest"
        xmlns:Generic="clr-namespace:System.Collections.Generic;assembly=mscorlib" Title="MainWindow" Height="550" Width="525">
    <Window.Resources>
        <FontFallbackTest:TestFont x:Key="TestFont2"/>
    </Window.Resources>
    <Grid>
        <TextBlock FontSize="48" FontFamily="{StaticResource TestFont}">This is some text</TextBlock>

        <TextBlock Margin="0,100,0,0" FontSize="48" FontFamily="c:\windows\fonts\GOTHIC.TTF#Century Gothic, Wingdings">This is some text</TextBlock>
        
        <Label Content="This is some text" FontSize="48" Margin="0,200,0,0">
            <Label.FontFamily>
                <FontFamily xmlns:sys="clr-namespace:System;assembly=mscorlib">
                    <FontFamily.FamilyNames>
                        <sys:String x:Key="en-US">Century, Century Gothic, Century Schoolbook</sys:String>
                    </FontFamily.FamilyNames>
                    <FontFamily.FamilyMaps>
                        <FontFamilyMap Target="Century Gothic" />

                        <!-- used when Century Gothic is not available -->
                        <FontFamilyMap Target="Arial" />
                    </FontFamily.FamilyMaps>
                </FontFamily>
            </Label.FontFamily>
        </Label>
        
        <Label Margin="0,150,0,0" FontSize="48" FontFamily="{StaticResource TestFont2}">This is some text</Label>
    </Grid>
</Window>