Here we have both The Nature of the Soul and The Soul and Its Instrument (in PDF), and Le Sentier du Service in French, as well as links to other books in their respective languages below.
Lucille's writings in other languages
In Danish: http://www.detukendtes.dk/
In Norwegian: Visdomsforlaget
In Italian: Bookstore: http://www.fraternity.it/
In Spanish: Kindle: La Naturaleza del Almaand Nook: La Naturaleza del Alma