'Bottom, thou art translated.'

[Lalaith]

Tolkien did give us a hint about the Hobbits' usage - he once said/wrote (sorry, I don't have the exact quote or location at the moment) that the Hobbits only use the familiar pronoun. For that reason Pippin was considered royalty by the people of Gondor, because he addressed Denethor with the familiar pronoun! Only an equal would be allowed that privilege.

Yes, I remember that too...presumably Merry would have been the same with Theoden.
Can you remind me of the difference between Ihr and Sie?

I was wrong actually that there was no use of du/sie in the English original. I remember that there is a point in LotR where Eowyn addresses Aragorn as "thee". This is a more intimate form of address and it shifts the mood dramatically.