On Mac, when using Respondus LockDown Browser, students can't use the default key commands (Control-SPACE or Command-SPACE) to switch keyboard language input. They might need this when taking a test for a language class.
Tell students to change the keyboard shortcut to something else (we found using the CAPS-LOCK works).
Starting in macOS Sierra (10.12) by default you can switch between languages with Control-SPACE while previously it was Command-SPACE. Command-SPACE is now "Show Spotlight Search" which is restricted in LockDown Browser (understandably).
To change the keyboard shortcut go to: System Preferences, Keyboard, Input Sources, Shortcuts, and you can change which key commands cycle through the "input source" or "input menu" - this may be different for different version of macOS, so do some Google searches to figure it out.
NOTE: This only affects the Mac version of LockDown browser, not Windows. Hopefully, Respondus will fix this in future versions, but this work-around will do the trick for now.
I'm just posting this for others' benefit. We've figured it out... but it took a while. Hopefully I've included enough key words in here to help someone out in the future. I plan to notify Respondus.