C#多语言问题

我在combobox中选择语言，为什么用Groupbox中的内容不会改变。请高手指教：combobox选择代码如下：
        private void MultiLanguage_SelectedIndexChanged(object sender, EventArgs e)
        {
            System.ComponentModel.ComponentResourceManager resources = new System.ComponentModel.ComponentResourceManager(typeof(FrmLogin));
            
            if (this.MultiLanguage.SelectedIndex == 0)
            {
                System.Threading.Thread.CurrentThread.CurrentUICulture = new System.Globalization.CultureInfo("");
          
            }
            else if (MultiLanguage.SelectedIndex == 1)
            {
                Thread.CurrentThread.CurrentUICulture = new System.Globalization.CultureInfo("en-US");
            }
            else if (MultiLanguage.SelectedIndex == 2)
            {
                Thread.CurrentThread.CurrentUICulture = new System.Globalization.CultureInfo("zh-CN");
            }
            else if (MultiLanguage.SelectedIndex == 3)
            {
                Thread.CurrentThread.CurrentUICulture = new System.Globalization.CultureInfo("zh-CHT");

            }
            else if (MultiLanguage.SelectedIndex == 4)
            {
                Thread.CurrentThread.CurrentUICulture = new System.Globalization.CultureInfo("ja-JP");
            }
            else
            {
                Thread.CurrentThread.CurrentUICulture = Thread.CurrentThread.CurrentCulture;
            }

            foreach (Control item in Controls)
            {
                resources.ApplyResources(item, item.Name);
            }
            resources.ApplyResources(this, "$this");
        }

补充：.NET技术 ,  C#