Guide to the Names in the Lord of the Rings
Tolkien's instructions for translators of The Lord of the Rings.
Guide to the Names in the Lord of the Rings. J.R.R. Tolkien, ed. Christopher Tolkien, published in: A Tolkien Compass. Ed. Jared Lobdell, La Salle, Illinois: Open Court, 1975. (Note: The new reprint of this book does not contain Tolkien's "Notes on Nomenclature"!).
Also called "Notes on Nomenclature", sometimes just "Guide to Names".