The best way to change the way to shift between languages from the default is as follows:
Open System Preferences and tap Keyboard:
Then tap Shortcuts, then from the side list tap "Input Sources", then "Select Next Source":
*Note you will have to choose something like CNTRL-SHIFT-1 or another key combo than shift-space, but you can play around with it and find a combo that works for you.
Edit: If you want to do what you want by only pressing control shift, you might be able to do that by creating an applescript which toggles the languages and using a 3rd party hot key app on the appstore. I don't advise this, but it would be conceivably possible. For the sake of convenience, I have attached such an applescript that you can use for this purpose where if you map say control shift to this applescript, it will execute the CMD space code (or you can change it another code which doesn't conflict with spotlight (my personal recommendation):
tell application id "com.apple.systemevents"
keystroke (key code 49 using command down)