I found a solution. I unchecked "Use system keyboard layout" under Advanced in UBus Preferences.
I checked "Show icon on system tray" under General. In Keyboard Preferences, under Layouts, I removed all keyboards except my main one. Now, all input methods are accessible with Super+Space, and (as an improvement from Trisquel 7) each icon for each input method has an easily viewable label in big letters. (Before, each input method had the same icon, and then a small text below it saying what it actually was.) In addition, there are new input methods for things I never got to type, like International Phonetic Alphabet and kaomoji. I haven't found an emoji input method yet, though.
