I don’t see an answer to the question that actually answers the question, in spite of the issues being marked as “closed,” so I hope to get the right answer here by asking it myself.
I have the default installation of LO that was there when I installed the default desktop environment and opened LibreOffice. I haven’t changed or added anything. Extension Manager shows only two items, Solver for Non-Linear Programming, and Wiki Publisher. There’s nothing about language tools or dictionaries here. When I click on the “add” button it assumes I’ve already downloaded it and/or have it somewhere. Do I? I don’t know.
The Tools / Language settings all say “English (USA)”. But the Tools / Spelling language pulldown only includes English-UK, which is checked, but in any event does not find any misspelled words at all. There are no red squigglies, in spite of having automatic spell checking enabled.
So I guess I’d just like to know what I need to download in order to get the English dictionary that I need to install. Or, if I already have it, where do I have it, and why wasn’t it installed or enabled on startup? Shouldn’t this be kind of a default thing? I’ll keep looking elsewhere as well, and will let you know if I solve it, but if you can point me to this answer, and where to find such answers in the future, it would be appreciated. I seem to have been unable to craft the correct search term that would bring me the answer I seek… a bit frustrating!