Can not switch imput method to chinese input method

Question

I developed a windows form program (language is C#, .net framework is 4.5) that can switch input method to Chinese input method programmatically when users press a specific shortcut(left ctrl + right arrow). this program can work well on Windows 10/11. but yesterday a user told me that he bought a MAC and install windows 10 and iOS on this same computer. my program still can run and work on this computer, but when this user pressed the shortcut and try to switch input method to Chinese input method, there is a exception was thrown.

the way to switch input method is to send message, like below:

public partial class Form1 : Form  
{  
	public class WinApi  
	{  
		[DllImport("user32.dll", CharSet = CharSet.Auto)]  
		public static extern IntPtr PostMessage(IntPtr hwnd, int msg, int wParam, IntPtr lParam);  
		[DllImport("user32.dll", CharSet = CharSet.Auto)]  
		public static extern IntPtr PostMessage(IntPtr hwnd, uint msg, IntPtr wParam, IntPtr lParam);  
		[DllImport("user32.dll")]  
		public static extern IntPtr LoadKeyboardLayout(string pwszKLID, uint Flags);  
	}  
	public const int WM_INPUTLANGCHANGEREQUEST = 80;  
	public enum InputMethod  
	{  
		Chinese,  
		English  
	}  
	private static IntPtr HWND_BROADCAST = (IntPtr)0xffff;  
	private static string en_US = "00000409"; //英文  
	private static string cn_ZH = "00000804";  
	private static uint KLF_ACTIVATE = 1;  

	...  
	public void SetImpitMethod(InputMethod im)  
	{  
		string imName = (im == InputMethod.Chinese) ? cn_ZH : en_US;  
		IntPtr ptr = WinApi.LoadKeyboardLayout(imName, KLF_ACTIVATE);  

		WinApi.PostMessage(HWND_BROADCAST, WM_INPUTLANGCHANGEREQUEST, IntPtr.Zero, ptr);  
	}  
	...  
}  

what I did is try to catch this exception, but I did not make, this is very weird. the exception is System.Globalization.CultureNotFoundException. the exception message is Chinese:不支持区域性, i try to translate it to English: No culture support. What I guess is that MAC does not support this feature but I am not sure it is correct or wrong. So far I have no any idea to solve this problem.

thanks for any suggestions and tips.