Log in at https://www.ea.com/ - Upper right corner, click on the Profile link > Account Settings. Make sure Regional Settings are set to China and Traditional Chinese. Keep the Origin and Game client settings you have (Traditional Chinese). Now, log out of everything.
Navigate to the game folder's Locale folder. On a PC, the default location is C:\Program Files (x86)\Origin Games\SimCity\SimCityData\Locale. I am sorry that I do not know exactly where this is on a Mac, but it should be somewhere in the application folder. Rename Locale folder to Old_Locale, or move it somewhere else as a backup.
Log in to Origin client, then right-click the SimCity icon and choose "Repair". This should download a fresh copy of the Chinese language pack. Once the repair completes, launch the game again. 
If you experience any crashes or problems after this repair, please reply back and let us know exactly what happens - does it lock up, does it give an error message? Screen shots of any error messages could be helpful. Also, please provide more information about your Mac. Instructions on how to do so here - https://answers.ea.com/t5/The-Sims-Mac/READ-FIRST-Sims-4-Mac-Help-Guides-and-Troubleshooting/m-p/4612396/highlight/true#M162