Shift + Control + Space doesn't seem to work anymore.
Using Mojave 10.14.1 at the moment. I checked to see the mentioned shortcuts in the "System Preferences" --> "Keyboard" --> "Shortcuts" tab and then selected "Input Sources" on the left side menu:
(I) Select the previous input source: Control + Space
(II) Select next source in input menu: Control + Option + Space
(The first one was checked by default - even though I only 1 layout.)
My first post on StackExchange. I hope it was helpful!