Can't see this emoji  on macOS I just found I can't see this emoji  (Flag of ROC — Republic of China, Taiwan), which is rendered as a cross in a box, on my mac with macOS 10.13.5.

I bought my Mac in China, but my language regional preferences are all set to the U.S. Is there any way to make this emoji visible again?

Here is a screen capture of how this is displayed on my computer:
Probably connected to where you bought the machine.  From Emojipedia:

The flag for Taiwan, which may show as the letters TW on some platforms.
This flag is hidden from the emoji keyboard on iOS devices where the region is set to china. Chinese iPhones won't display this flag and will instead show a missing character tofu (□).