I have been working on collection Christmas songs for a couple of years (on and off, of course); mainly out of an interest in folk music. After each song will be found a letter: L for Latin, F for French, E for English, W for Welsh, G for German, A for American (these are generally pop songs), S for Scottish, for the songs whose origin I know.

A | B | C | D | E | F | G | H | I | J | K | L | M
N | O | P | Q | R | S | T | U | V | W | X | Y | Z

A
Adeste Fideles: O Come All Ye Faithful [L]
Angels From the Realm of Glory
Angels We Have Heard on High
Angelus ad Virginem [L]
As Lately We Watched
As With Gladness Men of Old
Auld Lang Syne [S]
Away in a Manger

B
Blow, Blow, Thou Winter Wind
Boar's Head Carol [E]
Break Forth Heavenly Light
Bring a Torch

C
Carol of the Bells
Carol of the Birds
Caroling, Caroling
Cherry Tree Carol
Chipmunk Song
Chorus Novae Ierusalem
Christ Was Born on Christmas Day
Christians Awake
A Christmas Carol [E]
The Christmas Song [A]
Corde natus ex parentis [L]
The Coventry Carol [E]

D
Deck the Halls (Oer yw'r gwr sy'n methu caru) [W]
Dies Irae [L]
Ding Dong Merrily On High
Do You Hear What I Hear? [A]
Dormi Iesu [L]

E
Es Ist Ein Ros Entsprungen (Lo, How a Rose E're Blooming) [G]

F
Feliz Navidad
First Noel, The
Friendly Beasts
From Heaven High I Come
Frosty the Snowman

G
Gentle Mary Laid Her Child
Gloria Laus et Honor
Gloucestershire Wassail 
Go Tell It On the Mountain
God Rest You Merry, Gentlemen 
Good Christian Men, Rejoice 
Good King Wenceslas 
Gower Wassail 

H
Happy Xmas (War is Over)
Hark! The Herald Angels Sing 
Have a Holly Jolly Christmas
Have Yourself a Merry Little Christmas
Here Comes Santa Claus
Here We Come A-Wassailing
Herod and the Cock 
Holly and the Ivy, The
How Brightly Beams The Morning Star 

I
I Heard the Bells on Christmas Day
I Saw Three Ships
I Wonder as I Wander
Il Est Ne
I'll Be Home For Christmas [A--pop]
It Came Upon A Midnight Clear
It's Beginning to Look a Lot Like Christmas [A--pop]

J
Jingle Bells [A--folk]
Jolly Old Saint Nicholas
Joy To The World

L
Let It Snow [A--pop]
Little Drummer Boy
Lully, Lully Lu [E]
Lo, How a Rose E're Blooming [G]

M
March of the Three Kings
Minuit, Chrétiens!: Cantique de Noël: O Holy Night [F]
Most Wonderful Time of the Year [A--pop]

N
No Place Like Home for the Holidays [A--pop]

O
O Christmas Tree
O Come All Ye Faithful: Adeste Fideles [L]
O Come, Little Children
O Come O Come Emmanuel: Veni Veni Emmanuel [L]
O Holy Night: Cantique de Noel: Minuit, Chretiens! [F]
O Little Town of Bethlehem (versions 1 & 2)
O Quanta Qualia [L]
O Sanctissima [L]
O Tannenbaum: O Christmas Tree [G]
Oer yw'r gwr sy'n methu caru: Deck the Halls [W]

P
Personent Hodie [L]
Puer Nobis Nascitur [L]

Q
Quem Pastores Laudavere [L]

R
Riu Riu Chiu [Sp]
Rudolph the Red-Nosed Reindeer [A--pop]

S
Santa Claus is Coming to Town [A--pop]
Shepherds, Shake Off Your Drowsy Sleep
Silent Night (Stille Nacht, Heilige Nacht!) [G]
Sleep, Holy Babe
Sleigh Ride
Stabat Mater Delarosa [L]
Stille Nacht: Silent Night [G]

T
Twelve Days of Christmas, The [E]

U
Up on the Housetop

V
Veni Veni Emmanuel: O Come O Come Emmanuel [L]

W
Wassail Song, The [E]
Wassail, Wassail [E]
Watchman, Tell Us of the Night 
We Need a Little Christmas [A--pop]
We Three Kings of Orient Are
We Wish You a Merry Christmas [E]
What Child Is This? [E]
While Shepherds Watched Their Flocks
White Christmas [A--pop]
Winter Wonderland [A--pop]
Wren Song, The [I]

Z
Zither Carol (Girls and Boys, Leave Your Toys) [A--folk]