When I was a tall (5"11') skinny (130 lbs) gangly boy of 13, I started First Year Latin in eighth grade. Our book had as an inside front cover the music and words (in Latin) of the carol that I only knew to that time as O Come All Ye Faithful. To discover that it was originally written in this strange old language I was only beginning to be acquainted with was an eye-opener. Ever since, I sing it to the Latin words in church (very softly not to be heard due to people thinking I'm strange [which I am] and because my singing is SO terrible.)
It was also my introduction to the concept of translating poetry. I saw for the first time how the translator (Frederick Oakeley, a British Catholic priest 1841) had to change from literal meaning to something that would fit the scan. I won't supply the translation, you all know it enough. I do invite those with a smattering or more of Latin to try to follow, it is wonderfully written.
I will point out two interesting parts of Oakeley's translation:
The very first word, adeste means arise not O come as the refrain Venite does.
The last word of the refrain, Dominum translates completely and accurately as Lord. But Dominum is a three syllable word sung as four syllables (do-o-mi-num). Stretching Lord to four syllables is a challenge so Oakeley expanded it to Christ the Lord, three syllables retaining a double first with Chri-ist.
1. Adeste Fideles laeti triumphantes, Venite, venite in Bethlehem.
Natum videte, Regem Angelorum;
Refrain
Venite adoremus,
venite adoremus,
venite adoremus
Dominum!
2. Deum de Deo, lumen de lumine, gestant puellae viscera.
Deum verum, genitum non factum; (refrain)
3. Cantet nunc io chorus Angelorum, cantet nunc aula caelestium:
Gloria in excelsis Deo!
4. Ergo qui natus, die hodierna, Jesu, tibi sit gloria.
Patris aeterni Verbum caro factum;
5. En grege relicto, Humiles ad cunas, vocati pastores approperant.
Et nos ovanti gradu festinemus;
6. Aeterni Parentis splendorem aeternum, velatum sub carne videbimus.
Deum infantem, pannis involutum;
7. Pro nobis egenum et foeno cubantem, piis foveamus amplexibus.
Sic nos anamtem quis non redamaret?
8. Stella duce, Magi, Christum adorantes, aurum, thus, et myrrham dant munera.
Jesu infanti corda praebeamus;
Eulalia, I confess that when I sing it, I use Classic pronunciation not the Medieval that is more correct since it wasn't written any before 1700. But I can't change wenite to venite or Angelorum to Anjelorum.