I18N

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="Languages" value="en-US.xaml"/>
  </appSettings>
</configuration>

protected override void OnStartup(StartupEventArgs e)
        {
            base.OnStartup(e);

            //第一种方式就是用配置文件 配置
            string appLang = ConfigurationManager.AppSettings.Get("Languages");
            App.Current.Resources.MergedDictionaries.Add(new ResourceDictionary() { Source = new Uri(appLang, UriKind.RelativeOrAbsolute) });
            //第二种方式 就是获取当前系统的语言
            string lang = System.Globalization.CultureInfo.InstalledUICulture.Name.ToString(CultureInfo.InvariantCulture);
            switch (lang)
            {
                case "zh-CN":
                    App.Current.Resources.MergedDictionaries.Add(new ResourceDictionary() { Source = new Uri("zh-CN.xaml", UriKind.RelativeOrAbsolute) });

                    break;
                case "en-US":
                    App.Current.Resources.MergedDictionaries.Add(new ResourceDictionary() { Source = new Uri("en-US.xaml", UriKind.RelativeOrAbsolute) });

                    break;
                default:
                    App.Current.Resources.MergedDictionaries.Add(new ResourceDictionary() { Source = new Uri("en-US.xaml", UriKind.RelativeOrAbsolute) });

                    break;
            }
        }

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:sys="clr-namespace:System;assembly=mscorlib">

  <sys:String x:Key="Window1Title">Window</sys:String>
  <sys:String x:Key="UserLog">UserLogin</sys:String>
  <sys:String x:Key="UserCode">UserCode</sys:String>
  <sys:String x:Key="UserName">UserPwd</sys:String>
  <sys:String x:Key="BtnLoginOk">Login</sys:String>
  <sys:String x:Key="BtnLoginCancel">Cancel</sys:String>
  <sys:String x:Key="BtnzhCN">Chinese</sys:String>
  <sys:String x:Key="BtnenUS">English</sys:String>

</ResourceDictionary>

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:sys="clr-namespace:System;assembly=mscorlib">

  <sys:String x:Key="Window1Title">窗体</sys:String>
  <sys:String x:Key="UserLog">用户登录</sys:String>
  <sys:String x:Key="UserCode">用户名</sys:String>
  <sys:String x:Key="UserName">密码</sys:String>
  <sys:String x:Key="BtnLoginOk">登录</sys:String>
  <sys:String x:Key="BtnLoginCancel">取消</sys:String>
  <sys:String x:Key="BtnzhCN">中文</sys:String>
  <sys:String x:Key="BtnenUS">英文</sys:String>

</ResourceDictionary>

<Window x:Class="I18N.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="{DynamicResource Window1Title}">
  <Grid HorizontalAlignment="Center" VerticalAlignment="Center">
    <GroupBox Header="{DynamicResource UserLog}">
      <Grid>
        <Grid.RowDefinitions>
          <RowDefinition Height="45*" />
          <RowDefinition Height="48*" />
          <RowDefinition Height="58*" />
          <RowDefinition Height="100*" />
        </Grid.RowDefinitions>
        <TextBlock Grid.Row="1"
                   Margin="36,22,0,0"
                   HorizontalAlignment="Left"
                   VerticalAlignment="Top"
                   Text="{DynamicResource UserCode}"
                   TextWrapping="Wrap" />
        <TextBlock Grid.Row="2"
                   Margin="36,23,0,0"
                   HorizontalAlignment="Left"
                   VerticalAlignment="Top"
                   Text="{DynamicResource UserName}"
                   TextWrapping="Wrap" />
        <TextBox Grid.Row="1"
                 Width="120"
                 Height="23"
                 Margin="125,22,0,0"
                 HorizontalAlignment="Left"
                 VerticalAlignment="Top"
                 Text="TextBox"
                 TextWrapping="Wrap" />
        <TextBox Grid.Row="2"
                 Width="120"
                 Height="23"
                 Margin="125,23,0,0"
                 HorizontalAlignment="Left"
                 VerticalAlignment="Top"
                 Text="TextBox"
                 TextWrapping="Wrap" />
        <Button Grid.Row="3"
                Width="75"
                Margin="78,29,0,0"
                HorizontalAlignment="Left"
                VerticalAlignment="Top"
                Content="{DynamicResource BtnLoginOk}" />
        <Button Grid.Row="3"
                Width="75"
                Margin="192,29,0,0"
                HorizontalAlignment="Left"
                VerticalAlignment="Top"
                Content="{DynamicResource BtnLoginCancel}" />
        <Button Name="btnenUS"
                Width="75"
                Margin="301,10,0,0"
                HorizontalAlignment="Left"
                VerticalAlignment="Top"
                Click="btnenUS_Click"
                Content="{DynamicResource BtnenUS}" />
        <Button Name="btnzhCN"
                Width="75"
                Margin="221,10,0,0"
                HorizontalAlignment="Left"
                VerticalAlignment="Top"
                Click="btnzhCN_Click"
                Content="{DynamicResource BtnzhCN}" />

      </Grid>
    </GroupBox>
  </Grid>
</Window>

using System;
using System.Windows;

namespace I18N
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void btnzhCN_Click(object sender, RoutedEventArgs e)
        {
            App.Current.Resources.MergedDictionaries.Add(new ResourceDictionary() { Source = new Uri("zh-CN.xaml", UriKind.RelativeOrAbsolute) });
        }

        private void btnenUS_Click(object sender, RoutedEventArgs e)
        {
            App.Current.Resources.MergedDictionaries.Add(new ResourceDictionary() { Source = new Uri("en-US.xaml", UriKind.RelativeOrAbsolute) });
        }
    }
}