Tolkien actually said that he should have used "dwarfs".
"No reviewer (that I have seen), although all have carefully used the correct dwarfs themselves, has commented on the fact (which I only became conscious of through reviews) that I use throughout the ‘incorrect’ plural dwarves. I am afraid it is just a piece of private bad grammar, rather shocking in a philologist; but I shall have to go on with it."
https://jakubmarian.com/dwarves-or-dwarfs-which-spelling-is-correct/
(, Mon 25 Sep 2017, 11:20, Share, Reply)