How to configure your default location in kindle to avoid unrecognized characters?

You may find there are some unrecognized characters (displayed by squares) on your kindle when using foreign languages such as Chinese. Let's take Chinese for example.

1. Go to home by pressing "home"key.
2. press key "enter" 
3. ;debugOn      
4. ~changeLocale zh-CN
5. ;debugOff

Note: step 3-5 should be followed by pressing key "enter", also letter case is sensitive (Capital letters are strict).

After you'v done with these steps, you should be able to see no squares characters.