They just don’t want people to complain about dishes they’re not used to. If you specifically ask for it then that’s enough to show that you’re specifically seeking it out. Also keep in mind not all Chinese restaurants do this, it’s normally the authentic really big restaurants that would have it. One way to tell is if you see dishes that aren’t on the menu others are eating or in pictures. Also that menu might be in Chinese only.
They would generally know if you are speaking Chinese. Otherwise “I would like to see the secret Chinese menu.” would probably work, if they have one.
I don’t speak Mandarin so the first option wouldn’t work. If I used the second option though they’d be like, “How did our secret get out?!”
They just don’t want people to complain about dishes they’re not used to. If you specifically ask for it then that’s enough to show that you’re specifically seeking it out. Also keep in mind not all Chinese restaurants do this, it’s normally the authentic really big restaurants that would have it. One way to tell is if you see dishes that aren’t on the menu others are eating or in pictures. Also that menu might be in Chinese only.