Judah's works include the translation into Hebrew of the following:
Bahya ibn Paquda's Chovot ha-Levavot. The Arabic title of this work was "Al-Hidayah ila Fara'id al-Qulub." In English, 'The Duties of the Heart'.
Solomon ibn Gabirol's Tikkun Middot ha-Nefesh.
Judah ha-Levi's Kitab al-Ḥujjah, under the title Sefer ha-Kuzari. In this instance as well, Judah's translation drove that of his rival, Judah ibn Cardinal, out of the field, so that only a small portion of the latter's work has been preserved.
Two works by Ibn Janah:
Saadia's Kitab al-Amanat wal-I'tiḳadat, under the title Sefer ha-Emunot weha-De'ot.
Testament
Judah's ethical will, with its homely style and frankness, is one of the most interesting in this class of literature. It gives insight into the soul of the man and his relation to his son, also a scholar and translator, Samuel. Against the latter his chief complaint is that he never initiated his father into his literary or business affairs, never asked for his advice, and, in fact, hid everything from him. He recommends Samuel to practise writing in Arabic, since Jews like Samuel ha-Nagid, for example, attained rank and position solely through being able to write in that language. He exhorts him to morality and to the study of the Torah as well as of the profane sciences, including medicine. He is to read grammatical works on Sabbaths and festivals, and is not to neglect the reading of "Mishle" and of "Ben Mishle." In regard to his medical practise he gives his son sage advice. He further advises his son to observe rigorously the laws of diet, lest he, like others, become ill frequently in consequence of intemperate and unwholesome eating, which would not fail to engender mistrust in him as a physician on the part of the general public. Interesting are Judah's references to his library as his "best treasure", his "best companion", and to his book-shelves as "the most beautiful pleasure-gardens." He adds:
I have collected a large library for thy sake so that thou needest never borrow a book of any one. As thou thyself seest, most students run hither and thither searching for books without being able to find them.... Look over thy Hebrew books every month, thy Arabic ones every two months, thy bound books every three months. Keep thy library in order, so that thou wilt not need to search for a book. Prepare a list of the books on each shelf, and place each book on its proper shelf. Take care also of the loose, separate leaves in thy books, because they contain exceedingly important things which I myself have collected and written down. Lose no writing and no letter which I leave thee.... Cover thy book-shelves with beautiful curtains, protect them from water from the roof, from mice, and from all harm, because they are thy best treasure.
His fine linguistic sense and his conception of the art of translating are shown by his counsels on this subject.
