When I installed 16.04, I mistakenly chose the German keyboard layout. My computer is a Japanese computer with Japanese keys, but I regularly use several languages. How can I change the default system layout for all of my languages without reinstalling the OS? I cannot for the life of me find a GUI or CLI way to do this. Many thanks for your help.
Ubuntu – How to change default keyboard layout (not input method) in Ubuntu 16.04
I'm not able to reproduce the problem you have mentioned in comments, i.e. that enabling a Japanese keyboard layout wouldn't make a difference. I added Japanese, and the resulting keyboard layout looks like this:
Then I opened gedit, switched to "Ja" via the input source indicator, and the expected characters according to the image above appeared when I typed.