How can I set up a keyboard shortcut for switching input source?

Solution 1:

Go to System Preferences → Keyboard → Shortcuts → Input Sources and define a keyboard shortcut there. As you only have two sources, set a single shortcut for one of the options, then pressing the shortcut will toggle the input sources.

Solution 2:

grgarside's answer was great.

Here is an another solution for multilingual user. If you want to switch among three or more input methods quickly or switching to a specific input method by shortcut directly, you may try IMEShortcuts (disclaimer: I'm the IMEShortcuts creator)

It allows you map a shortcut to a input method. You can switch to a specific method immediately by you-defined shortcut without using cmd+space to rotate input methods. It works well on OSX 10.9 ~ 10.12.

Please have a try, I'm glad to hear your feedback. Thanks