Left pane in shortcuts of keyboard system preferences doesn't slide
It has been solved by putting English first in the list of languages in system preferences, and restarting the computer. 

When setting the system language back to Spanish, this bug returns. It is way too unlikely to get Apple to attend via http://bugreport.apple.com, so it seems application shortcuts are not available in macOS Sierra in Spanish, at least for some systems. Just in case it affects the bug, the other languages I have down the list are Italian and French.