How can I hide the US units on the ScaleLine?
You have to change the style of the scaleline.For example, here is a ScaleLine template showing only Metrics Units, localizing the units and displaying the text in the center of the scale line:<esri:ScaleLine.Template>
<ControlTemplate TargetType="esri:ScaleLine">
<Grid x:Name="LayoutRoot">
<Grid.Resources>
<converters:ObjectToObjectConverter x:Key="UnitsConverter">
<ResourceDictionary>
<sys:String x:Key="Meters">Métres</sys:String>
<sys:String x:Key="Kilometers">Kilométres</sys:String>
</ResourceDictionary>
</converters:ObjectToObjectConverter>
</Grid.Resources>
<StackPanel HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" >
<StackPanel x:Name="MetricNotchs" Orientation="Horizontal">
<Rectangle x:Name="LeftTopNotch" Width="2" Fill="{TemplateBinding Foreground}" Height="5" Stroke="{TemplateBinding Foreground}" VerticalAlignment="Bottom" />
<Grid Width="{Binding MetricSize, RelativeSource={RelativeSource TemplatedParent}}">
<StackPanel x:Name="MetricText" Orientation="Horizontal" HorizontalAlignment="Center" >
<TextBlock Text="{Binding MetricValue, RelativeSource={RelativeSource TemplatedParent}}"/>
<TextBlock Text="{Binding MetricUnit, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource UnitsConverter}}"/>
</StackPanel>
</Grid>
<Rectangle x:Name="RightTopNotch" Width="2" Fill="{TemplateBinding Foreground}" Height="5" Stroke="{TemplateBinding Foreground}" VerticalAlignment="Bottom"/>
</StackPanel>
<StackPanel x:Name="ScaleLineBlock" Orientation="Horizontal">
<Rectangle x:Name="NotchsWidth" Fill="{TemplateBinding Foreground}" Height="2" Stroke="{TemplateBinding Foreground}" Width="4"/>
<Rectangle Fill="{TemplateBinding Foreground}" Height="2" Stroke="{TemplateBinding Foreground}" Margin="0" HorizontalAlignment="Left"
Width="{Binding MetricSize, RelativeSource={RelativeSource TemplatedParent}}" />
</StackPanel>
<StackPanel x:Name="BottomNotchs" Orientation="Horizontal">
<Rectangle x:Name="LeftBottomNotch" Width="2" Fill="{TemplateBinding Foreground}" Height="5" Stroke="{TemplateBinding Foreground}" VerticalAlignment="Top" />
<Grid x:Name="PaddingLeftBottomNotch" Width="{Binding MetricSize, RelativeSource={RelativeSource TemplatedParent}}" />
<Rectangle x:Name="RightBottomNotch" Width="2" Fill="{TemplateBinding Foreground}" Height="5" Stroke="{TemplateBinding Foreground}" VerticalAlignment="Top"/>
</StackPanel>
</StackPanel>
</Grid>
</ControlTemplate>
</esri:ScaleLine.Template>
