How can I create a shortcut to switch to a specific keyboard layout?
You'll notice that the shortcuts only appear when you're using Chinese input methods. They don't appear otherwise per this article from Apple's knowledgebase.

I can't find any way around this limitation. However, there is a built-in keyboard shortcut for switching between keyboard layouts, if not for switching to a specific keyboard layout. You can find this shortcut in System Preferences -> Keyboard -> Keyboard &amp; Text Input: