I have been having an issue regarding keyboard short-cut to change input source between Japanese and English on a new iMac running on Sierra. On my old Mac, I used "command+space" (Fig. 1) to change the input source, but now on Sierra I have to use "control+space" (Fig. 2), which is quite inconvenient. Could someone help me how to set my system so that I can use "command+space" to change the input source?
You are in the right place, but the wrong selection.
Select "Spotlight" from the list on the left. You can then uncheck the shortcut for Command Space allowing you to assign that to the shortcut you want to.
Looks like it doesn't want to work on my Mojave. After unchecking Command+space for spotlight, i still don't receive option to add it to change the source input shortcut. Please, advice
You should select shortcut you want to change and press ENTER (not double click, double click do nothing) to be able to change this selected shortcut. Work this way on Mac OS Mojave 10.14.5, don't know if its relevant for older or future version of Mac OS.