You can restore the Taiwan flag emoji ("🇹🇼") on a Chinese Mac (where it shows as an X in a box by default) by running the command sudo defaults write /Library/Preferences/.GlobalPreferences.plist Country CA (replace CA with the two-letter country code of any other country except for China) and changing the country to the same one you set using the command in System Settings, then restarting the computer. The Taiwan flag emoji should then be visible.