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Hey there quynhchau,

I see that you are experiencing some issues when attempting to login to your Mac. I believe that I have an article that will help you address this issue, and it can be found below:

The text of the login window will be displayed in the language that was selected when Mac OS X was installed, or the language selected the first time Mac OS X was started on a new Mac. Learn how you can change the language used for the login window.

There are two ways to change the language of the login window:

• Reinstall OS X and select the desired language during installation
• Or, use the steps below depending on your version of OS X.

OS X: How to change the language displayed in the login window - Apple Support

https://support.apple.com/en-us/HT202036

Re-installing El Capitan should not affect your user data, but be sure to create a backup first just in case. Thanks for using the Apple Support Communities!