Can I specify the decimal precision of the converted value?

You can change the decimal precision for the target unit (or unit table) in the
Preferences > General tab.

How can I change the unit order and visibility?

You can change the unit order and visibility in the
Preferences > Customize tab.

How can I set keyboard shortcut to toggle app?

You can set the keyboard shortcut in the Preferences > General tab.

[⌥⇧C] is set by default.
Click the 'x' on the right registered shortcut,
then press new shortcut over 'Press Shortcut' placeholder.

Want to use dock icon instead of menu bar icon

You can choose the dock icon option in the Preferences > General tab.

Check the 'Use dock icon when unpinning',
then click the icon from the main window to unpin the app.

Want to change the language of the app

g Converter uses the system language by default if the language is supported.

To change the language of the app,
open the System Preferences > Language & Region > Apps tab,
click the '+' button below.

Select 'g Converter' from the application and then select the language you want.