"Deck the Halls" is another example of a popular English-language carol that has been translated into Latin. I've now found several different versions to share with you here. You can find information about the English carol "Deck the Hall," along with the English lyrics, at the Hymns and Carols of Christmas website. There is also a Wikipedia article about this song.
Version 1 (translated by Stanford Miller, widely found on the Internet)
If you are curious about the etymology of the Latin word for "holly," aquifolia, it has as its roots acu- (aqu-), meaning "sharp" (as in the English word "acute") and folia, "leaves" (as in the English word "foliage") - because of the sharp holly leaves! Versions of this song on the Internet are plagued by a recurring typographical error, reading "aquafolia," which is not a Latin word. In addition, versions on the Internet read ornatis, "you are decorating," but I have changed that to the imperative ornate, "decorate," following the English. Admittedly, this does obscure the rhyme - so if you want to emphasize the rhyme, by all means read ornatis instead! (Thanks to Chris for his comment about that; see below.)
Aquifolia ornate Fa la la la la, la la la la Tempus hoc hilaritatis. Fa la la la la, la la la la Vestes claras induamus; Fa la la la la, la la la la Cantilenas nunc promamus. Fa la la la la, la la la la
Domus visco exornemus, Fa la la la la la la la la Iubilemus, esultemus, Fa la la la la la la la la Habitu nos induamus, Fa la la la la la la la la Iesum genitum canamus, Fa la la la la la la la la Festum grande celebremus, Fa la la la la la la la la In promiscuo cantemus, Fa la la la la la la la la Me sequimi canentem, Fa la la la la la la la la Me de festo hoc loquentem, Fa la la la la la la la la Annus iterum transivit, Fa la la la la la la la la Novus perbrevi inibit, Fa la la la la la la la la Omnes alacres canamus, Fa la la la la la la la la Tempestatem rideamus, Fa la la la la la la la la
The following verses are not based on the traditional English lyrics to the carol, and their content is markedly religious. If anybody knows whether Maynard composed these verses in Latin himself, or whether they are based on an English version of the song, let me know!
Novis dat nunc canities, Saturnalia la-la la-la. pacem benevolentiae. Saturnalia la-la la-la. Donis Dei intersumus, Saturnalia la-la la-la. mensis plenis bonitatis, Saturnalia la-la la-la.
"God Rest You Merry, Gentlemen" is a very well-known English carol, and I've found two different Latin translations online. You can find detailed information about the English carol at the Hymns and Carols of Christmas website and in this Wikipedia article.
This carol is famously featured in Charles Dickens's A Christmas Carol.
Version 1 (Translated by J.C. Robertson)
O viri, este hilares et bono animo. Salvator Christus natus est hoc tempore festo, ut nos errantes liberet summo periculo. O laetissimum nuntium, laetissimum, O laetissimum nuntium.
[The "In Bethlehem" verse is not included] De caelo Pater misit in terram angelum, qui quosdam ad pastores afferret nuntium: in Bethlehem natum esse Ipsius filium. O laetissimum nuntium, laetissimum, O laetissimum nuntium.
[The "Fear not" verse is not included.] Quo cognito pastores, completi gaudio, relictis statim gregibus in imbre et in vento, approperant in urbem visendi studio. O laetissimum nuntium, laetissimum, O laetissimum nuntium.
Eo cum pervenissent, viderunt parvulum cubantem in praesaepio in faeno pecorum, dum mater nixa genibus adorat Dominum. O laetissimum nuntium, laetissimum, O laetissimum nuntium.
[The "With sudden joy" verse is not included.] Nunc collaudemus Dominum omnes qui adsumus, amore vero inter nos dilecti penitus. Nam omnium dierum hic est faustissimus. O laetissimum nuntium, laetissimum, O laetissimum nuntium. [The "God bless the ruler" verse is not included.]
Version 2 (Translated by Lillian Lawler)
Salvete, laeti comites. Nihil vos terreat. Nam Iesus Christus natus est ut omnes redimat, et in Satanae semitas errantes reducat. O nuntium gratissimum, gratissimum! O nuntium gratissimum!
Here is an instrumental version to sing along with:
Annie Lennox is singing in English; you can sing along in Latin!