OS X El Capitan Keyboard-switch Shortcut

Important: I'm going to skip to the part after you add a new keyboard input source. If, for some reason, you didn't add a new keyboard input source, here's where you go:

System Preferences > Keyboard > Input Source, then click the +

I’m making a Japanese Katakana flash card game using Rails; so it was mission critical that I have quick access to both the Japanese and U.S. keyboard.

When I looked at the shortcut command (option + command + spacebar), it didn’t work at all. Wtf.

Turns out OS X’s Spotlight feature was hogging it for a Finder command. Lame. I disabled the Finder command and violà!