When you log in ATT web page, click on your user name, and then click on the Preferences button.
Once there, click on the edit button.
Click on the Language drop-down menu, and select the desired language from the given list. Update changes by clicking on the Save button.
Click on the menu icon marked with three lines currently in the left upper corner of the screen.
Click on the Settings in the main menu.
Click on the Application Language, and select preferred language.