:s1: Ah! The joys of Latin revisited! Having done it for 3 years at school, your post brought back a lot of pleasant memories... However: using a title such as Quadraginta would make one appear pompous nowadays to most English speakers! As for those who would read such a book--if it was, e.g., Nawawi's Forty, calling it Nawawi's Quadraginta or, if my memory serves me correctly, Qaudragintae Nawawi, would be unintelligable to most. (p.s. have u been getting my emails? jawaab nadaaram, Aagha-ye-man!)
Quadraginta means 'Forty' in Latin. Just like Arbayin. Writing ‘forty’ in Latin makes it easy to use it as a proper noun; because using ‘forty’ without specifying ‘what’ seems like a hanging sentence. To wit: The Quadraginta is a magnificent book for beginners. The Forty is a magnificent book for beginners. The Forty Ĥadīth is a magnificent book for beginners. The Collection of Forty is a magnificent book for beginners. This also obviates the need to specify forty ‘what’ in other cases – like Arbaýīn of Imām Ghazāli is not just ĥadīth, even though it contains ĥadīth; we can simply say: ‘The Quadraginta’ of Imām Ghazali. It is a mind-trick, but it works. If it helps or is easier, we can try French: ‘Quarante.’ This raises the question, why not leave it at ‘Arbaýīn’ in Arabic? Perhaps, it is because English/French are related to Latin and anything said in Latin sounds profound... Quidquid latine dictum sit, altum sonatur