setting combobox default selectedindex
<ComboBox Width="125" Height="30" Margin="11,0,0,0"  x:Name="LanguageCombo"  SelectionChanged="LanguageCombo_SelectionChanged"  >
            <ComboBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <TextBlock Text="{Binding LangNameEnglish}" />
                        <!--<TextBlock Text="{Binding LastName}" Margin="5,0,0,0" />-->
                    </StackPanel >
</DataTemplate>
            </ComboBox.ItemTemplate>
        </ComboBox>

TranslationContext ctx=new TranslationContext();
           LoadOperation<Language> prd = ctx.Load(ctx.GetLanguagesQuery());
            LanguageCombo.ItemsSource = prd.Entities;