I have an iMac and want to share with a Chinese person. I know we can set up different users, but can each user have their own language file saved so that when one user logs in, the system is set for their language of choice?
Different user accounts on your iMac should be able to have separate languages and keyboard layouts set.
You'll want to create the account for the other user, login with that account, then click the Apple Menu and go to
System Preferences > Language & Region. From there, you can click the plus button to add a new language. Once you've selected their language, you can drag it to the top of the list so it's the top-most preferred language(these directions may vary slightly depending on your OS version).
Note that not all apps have support for all languages - your operating system will do its best to enforce your most preferred language.