public class KeyCodeToAscii {

	    [DllImport("User32.dll"]
	    public static extern int ToAscii(int uVirtKey, int uScanCode, byte[] lpbKeyState, byte[] lpChar, int uFlags);

	    [DllImport("User32.dll"]
	    public static extern int GetKeyboardState(byte[] pbKeyState);

	    public static char GetAsciiCharacter(int uVirtKey) {

		    var lpKeyState = new byte[256];
		    
            GetKeyboardState( lpKeyState );
		    
            var lpChar = new byte[2];

		    if ( ToAscii( uVirtKey, 0, lpKeyState, lpChar, 0 ) == 1) {
			    
                return Convert.ToChar( ( lpChar[0] ) );

		    } else {
			    
                return new char();
		    }
	    }

    }

public override void OnKeyDown( KeyEventArgs e ) {
    
    var keyChar = KeyCodeToAscii.GetAsciiCharacter( e.KeyValue );

    OnKeyPress( new KeyPressEventArgs( keyChar ) );
}

public void OnKeyPress( KeyPressEventArgs e ) {

    // ...
}

using System;
using System.Diagnostics;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Text;

namespace ComboBoxListRegion
{
	/// <summary>
	/// hook adapted from: http://stackoverflow.com/questions/370754/convert-a-keycode-to-the-relevant-display-character
	/// </summary>
	public class KeyboardHelper
	{
		[DllImport("user32.dll", CharSet = CharSet.Unicode, ExactSpelling = true)]
        private static extern int ToUnicodeEx(
            uint wVirtKey,
            uint wScanCode,
            Keys[] lpKeyState,
            StringBuilder pwszBuff,
            int cchBuff,
            uint wFlags,
            IntPtr dwhkl);

        [DllImport("user32.dll", ExactSpelling = true)]
        internal static extern IntPtr GetKeyboardLayout(uint threadId);

        [DllImport("user32.dll", ExactSpelling = true)]
        internal static extern bool GetKeyboardState(Keys[] keyStates);

        [DllImport("user32.dll", ExactSpelling = true)]
        internal static extern uint GetWindowThreadProcessId(IntPtr hwindow, out uint processId);

        public static string CodeToString(int scanCode)
        {
            uint procId;
            uint thread = GetWindowThreadProcessId(Process.GetCurrentProcess().MainWindowHandle, out procId);
            IntPtr hkl = GetKeyboardLayout(thread);

            if (hkl == IntPtr.Zero)
            {
                MessageBox.Show("Sorry, that keyboard does not seem to be valid.";
                return string.Empty;
            }

            Keys[] keyStates = new Keys[256];
            if (!GetKeyboardState(keyStates))
                return string.Empty;

            StringBuilder sb = new StringBuilder(10);
            int rc = ToUnicodeEx((uint)scanCode, (uint)scanCode, keyStates, sb, sb.Capacity, 0, hkl);
            return sb.ToString();
        }
	}
}

public override void OnKeyDown( KeyEventArgs e ) {
    
	string keyChar = KeyboardHelper.CodeToString( e.KeyValue );
	
	if (keyChar != String.Empty)
		OnKeyPress( new KeyPressEventArgs( (char)keyChar[0] ) );
}

public void OnKeyPress( KeyPressEventArgs e ) {

    // ...
}

public override void OnKeyDown(KeyEventArgs e)
{	
	if (!(this.ShowDescription && this.Description.Focused))
	{	
		if (e.KeyCode == Keys.Return)
		{
		  // ...
		}
		else if (e.KeyCode == Keys.Up)
		{
		  // ...
		}
		else if (e.KeyCode == Keys.Down)
		// ...
	}
	base.OnKeyDown(e);
}