Using shortcuts:
To select the input source you previously used, press Command-Space bar.
To select the next input source in the Input menu, press Command-Option-Space bar.
If Spotlight opens when you’re switching input sources, choose Apple menu > System Preferences, click Keyboard, and then click Keyboard Shortcuts. Select Spotlight on the left and deselect the Spotlight shortcut checkboxes on the right. Then, select Keyboard & Text Input on the left and select the “Select the previous input source” checkbox and the “Select the next source in Input menu” checkbox.