Today, I got asked by someone how to change the default language in Ubuntu. So, I took some time to do a screenshot and wrote a simple instruction, hope this will be useful.
Step 0: Make sure you are connected to the Internet
Step 1: Select Language Support from System > Administration
Step 2: Ignore or Install the first dialog
Step 3: Click on Install / Remove Languages
Step 4: Find your preferred language and click the check box, then Apply Changes
Step 5. Log out the current session and go back to the login page
Step 6. Click on your user name entry and type in your password
Step 7: Before you click on the login button, select your preferred language at the bottom
Step 8: Click Login now to Enter the system with your new language environment.