Jailbreak. It's not as powerful as the font hack. You can only able to change the reader font.
Eject your Amazon Kindle Keyboard.
Restart your Amazon Kindle:
Menu > Settings > Menu > Restart
- On your Amazon Kindle, press Home button to go to your home page.
This step is important to make sure the change you are going to do will take effect. If you are doing this while an eBook is open, the change will not take effect.
- Connect your Amazon Kindle to your computer with a USB cable.
- Open the folder in sequence : system > com.amazon.ebook.booklet.reader
- In the "com.amazon.ebook.booklet.reader" folder, open reader.pref file with a text editor.
- Add a new line to the file just before "FONT_FAMILY=" line:
- Replace FONT_FAMILY= with FONT_FAMILY=alt.
- Save and close the reader.pref file.
- At the root of your Kindle device, create a folder named fonts.
- In this folder, you will need to rename your custom fonts with specific names according to their styles.
- Regular : alt-Regulat.ttf
- Bold : alt-Bold.ttf
- Italic : alt-Italic.ttf
- Bold Italic : alt-BoldItalic.ttf
This customization of the reader.pref file will be reset if you try to change the typeface setting in the [AA] menu but changing the other settings should be fine.