I would like to test different layouts on my keyboard using a GUI, and I would preferably want to use the keyboard layout GUI that is shown during the installation of any Ubuntu-based distribution, because I found it to be very user-friendly.
This is the keyboard layout GUI that I'm referring to:
Is it possible to execute this application without having to follow the installation process?
Are there any other GUI-based alternatives for testing different keyboard layouts?
I am running Xubuntu 16.04.2 LTS
I'm not aware of any way to use the GUI of the installer after the installation.
In Xubuntu you can go to Settings -> Keyboard -> Layout, uncheck "Use system defaults", and add the layouts you want to test. Then you can add the Keyboard Layouts indicator to the panel and use it to switch between the layouts you added.