Leo XIII, best known among some Roman Catholics because his name is attached to the Bull which condemned Anglican Orders, deserves to be better known for his hymns. He wrote two of those which we use on the feast of the Holy Family.
Dulce fit nobis is a cut-down version of his Sacra iam splendent. Leo wrote it in the Sapphic Metre, which was either invented or brought into prominence by Sappho, a poetess of the Greek island of Lesbos around 600ish BC, and made popular in Latin by Catullus and Horace; a metre which has always been popular among schoolboys because it is one of the easier metres in which to write Latin. Perhaps that is why it became a popular metre in the Carolingian period; but Leo was too good a Latinist to have chosen it from such base motives. [Incidentally, you can always recognise it because it is the metre where the fourth line is shorter and goes Tumtitty Tumtum; e.g. English Hymnal 335 Wherefore, O Father, we thy humble servants, which was used (and probably written) to cover the silent repetition by the Anglican Catholic clergy of the Unde et memores etc of the Canon Romanus, the oblatory language of which it echoes.]
Back to Leo and his Holy Family hymn. He did bequeath a problem to the post-Vatican II revisers. He wrote that Mary, a good Mother and a good spouse, gave a helping hand to both Son and husband,
si potest curas relevare fessis
[ ................. happy
if she can lighten, with a friendly duty,
cares for the weary.]
But, apparently, 'fessis' suggests to the Francophone ear not 'weary' but 'buttocks'. So Dom Anselmo Lentini changed it to the problem-free word 'lassis', thus spoiling the alliterative "felix ... fessis" but sparing the blushes of that notoriously bashful constituency, the French clergy. (I will award the S Thomas's Order of Chastity, Fourth Class, which authorises you to have a pink pompom on your biretta, to any reader who can demonstrate that there is another language in which 'lassis' is even more indelicate than 'fessis' is in French.)
Seriously: Leo was a fluent French speaker. Yet, as a cultivated Latinist, he wrote "fessis" without a moment's anxiety. What sort of cultural shift has landed us with an 'emancipated' society in which the word is too sniggerworthy to be printable?