Add a filter to the command column in the RadGridView

 public partial class RadForm1 : Telerik.WinControls.UI.RadForm
 {
     public RadForm1()
     {
         InitializeComponent();
         this.radGridView1.EnableFiltering = true;
         this.radGridView1.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;

         CustomCommandColumn CommandColumn = new CustomCommandColumn();
         CommandColumn.Name = "LinkButon";
         CommandColumn.FieldName = "Country";
         CommandColumn.HeaderText = "Linke Git";
         CommandColumn.UseDefaultText = false;
         CommandColumn.AllowFiltering = true;

         // CommandColumn.FormatInfo = new System.Globalization.CultureInfo("tr-TR");
         this.radGridView1.Columns.Add(CommandColumn);
         this.radGridView1.EditorRequired += this.RadGridView1_EditorRequired;
         this.radGridView1.CellFormatting += this.RadGridView1_CellFormatting;
         this.radGridView1.CellBeginEdit += this.RadGridView1_CellBeginEdit;
         this.radGridView1.FilterChanged += this.RadGridView1_FilterChanged;
     }

     private void RadGridView1_FilterChanged(object sender, GridViewCollectionChangedEventArgs e)
     {

     }

     private void RadGridView1_EditorRequired(object sender, EditorRequiredEventArgs e)
     {
         var editManager = sender as GridViewEditManager;
         if (editManager == null || radGridView1.CurrentColumn.Name != "LinkButon")
         {
             return;
         }

         e.Editor = new RadDropDownListEditor();
         e.EditorType = typeof(RadDropDownListEditor);
     }

     private void RadGridView1_CellBeginEdit(object sender, GridViewCellCancelEventArgs e)
     {
         string msg = "";
         try
         {
             if (radGridView1.Columns[e.ColumnIndex].Name != "LinkButon")
             {
                 return;
             }

             var editor = radGridView1.ActiveEditor as RadDropDownListEditor;

             var dropDownElement = editor.EditorElement as RadDropDownListEditorElement;

             //string[] descs = IOC.linksData.getDescriptions(out msg);
             dropDownElement.DataSource = new object[] { "USA", "UK" };


         }
         catch (Exception ex)
         {
             msg = ex.Message.ToString();
         }
     }

     private void RadGridView1_CellFormatting(object sender, CellFormattingEventArgs e)
     {
         if (e.Row is GridViewDataRowInfo)
         {
             GridCommandCellElement commandCell = e.CellElement as GridCommandCellElement;
             if (commandCell != null)
             {
                 commandCell.CommandButton.Text = e.Row.Cells[4].Value.ToString();
             }

         }
     }

     private void RadForm1_Load(object sender, EventArgs e)
     {
         // TODO: This line of code loads data into the 'nwindDataSet.Employees' table. You can move, or remove it, as needed.
         this.employeesTableAdapter.Fill(this.nwindDataSet.Employees);


     }
 }
 public class CustomCommandColumn : GridViewCommandColumn
 {
     public CustomCommandColumn() : base()
     {
     }

     public CustomCommandColumn(string name) : base(name)
     {
     }

     public override bool AllowFiltering
     {
         get
         {
             return true;
         }
     }
 }