Thanks for your comments on the Swedish translation and your understanding of these passages,
Skip! Apparently Sweden must be the Shire, since the formal pronoun has disappeared there too!
I quite agree with you that Denethor and the Mouth use the familiar form as an insult - I do look forward to discussing those passages! Coming soon to a thread near you...
Formy, I checked the German translation of Appendix F, Section II, and it is precisely the same as the original. No changes there. I'm not familiar with the whole of the translated book, but I did look to see if Sam used a deferential form when speaking to Frodo, and that is not the case. Apparently the translator paid attention to Tolkien's words, and all of the hobbits use the familiar form.