Now any student of the Regency period is well aware that Christmas wasn't the big affair it became under the Victorians, who might be considered to have invented Christmas as we know it, but Advent was still a time for Christmas carols. However, many of the carols we find so familiar today were unknown in Britain until translated out of the German, and those we would recognise might well have been set to very unfamiliar tunes. 'Hark! The herald angels sing' for example, which might be still being sung as 'Hark how all the welkin rings' was sung to 'Nassau' which was suggested by Wesley, and was also the tune used for 'Christ the Lord is Risen today'. It does make sense that rural musicians liked to recycle tunes so they did not have to learn as many. After all, very few churches had an organ, never mind an organist, and most hymns were played by those who were nominally musical in the general populace, who probably could not read a note of music and learned the tunes by rote to play on their eclectic selections of rustic instruments.
It would not be until the late Regency and the end of the Georgian era that the usual suspects for 87:87:87 metre hymns were written, so no Cwm Rhonda, Hyfrodol or Blaenwern. Thus 'Love Divine' which could be used as a carol in Advent, would be sung to either 'Bithynia' or Purcell's 'Fairest Isle' the latter being the most familiar to most congregations of the time. It's easy to find on YouTube and isn't as dire as some hymn tunes of the day. 'Joy to the world' was certainly not the carillion of joy to which we sing it today. A lot of the tunes seem quite dirge-like to us nowadays! I listen to the original tune of 'Joy to the world' and feel depressed.
I do love the tune of 'Marching to Zion' though, it's so very restoration you half expect it to be bawdy.
However, the folk of the Regency era had a lot more freedom than during the Commonwealth; before 1700 only the Psalms of David were permitted by the Anglican church, and one authorised Christmas hymn; 'While Shepherds watched their flocks by night'. A supplement published in 1700 which included 'While Shepherds watched' and 15 other hymns, expanded the use of the psalms alone, though 'While Shepherds watched' is the only one of the sixteen that we still sing today.
The tradition of carolling [a word originally meaning a dance]seems to have survived the exigencies of the Commonwealth, and the medieval carols survived to be documented and used. I turned to the Oxford Book of Carols as a starting point, and then researched around them. The OCB is kind enough to have some information along with the oldest. Whether those using Latin were purely sung by scholars at first I do not know but there is some suggestion that they were known in the populace and were perhaps given rough translations by individual vicars for their congregation. I made free translations going back to first principles of both 'Adeste Fideles' and 'Veni Immanuel' whose tunes are original. I didn't get too carried away. There are more than the 3 verses we usually sing to Adeste Fideles, and not just the extra one for Christmas day itself. My Latin is a little doggy around the edges but probably no more so than the average vicar or squire translating for their people.
There are, extant, several translations of Veni Immanuel, and I'm most familiar with the one from the English Hymnal which I found when going back to the Latin to be seriously fanciful. However this should give an idea to anyone wanting to make up their own local translation ....
It may also be noted that some carols, like 'Tomorrow shall be my dancing day', a forerunner to 'Lord of the Dance', contained both Christmas and Easter components, and the appropriate verses were supposed to be sung at the appropriate times.
Adam lay ybounden
A virgin most pure [several tunes]
In dulci jubilo
I sing of a maiden that is makeless [makeless means unstained]
Lullay my liking
Oh wassail oh wassail [many different versions, and often used for 'Thomassing', begging alms on St Thomas' day, 21st December]
Puer Nobis Nascitur
Sans day carol
Shepherds arise [Sussex]
The Boar's Head carol
The Cherry Tree carol [almost as many versions as there are counties]
Tomorrow shall be my dancing day
More recent carols [W = by Wesley, IW = by Isaac Watts]
Behold the grace appears [for Christmas day]
Branch of Jesse's stem arise [W]
Hark! the glad sound, the saviour comes
Hark! the herald angels sing [W][for Christmas day]
Light of those whose dreary dwelling [W]
Love Divine, all loves excelling [W]
Joy to the world [IW]
Marching to Zion [IW]
On Jordan's bank, the baptist's cry
Shepherds rejoice [IW]
The seven joys of Mary
While Shepherds Watched
Ye simple men of hearts sincere [W]
The educated would also have known such French carols as 'Quelle est cette odour agreable' [sung to a tune adapted from Gay's 'Beggars' Opera', which is the tune we still know], 'Patapan' and 'Les Anges dans nos compagnes' but in general I think the populace would consider these most unpatriotic. Indeed, I wrote of a riot in 'Marianne's Misanthrope', engendered by the introduction of such a carol by an insensitive vicar.
This may not be an exhaustive list, but they were all I could find. I hope you will enjoy them, and also enjoy finding the ones I used in both 'Marianne's Misanthrope' and the purely Christmas novel recently released, 'Anne's Achievement' here for kindle and here for paperback