It seems that no one gets the benefit of spell-checking in LibreOffice on our Ubuntu computers. We have them generally set up with Canadian English as default languages, but apparently there is no spell checking for Canadian English.
The fix seems to be for each new user to do the following, within LibreOffice:
Go to Tools/Options/Language Settings/Languages. For "Default language for documents," pick English (USA) or English (UK).
It allows dozens of flavours of English, BUT spelling is disabled for all the ones that don't have the little blue tick ABC icon beside them.
That is not good, since in Canada we have spelling that is more flexible than US or UK. However, my question is how to set this up for everyone, at the system level, so that each user does not need to figure this out?