蛍の光 - AULD LANG SYNE

(STANZA)
Should auld acquaintance be forgot
and never brought to mind?
Should auld acquaintance be forgot 
for the sake of auld lang syne?

(REFRAIN)
For auld lang syne, my dear,
for auld lang syne...
We'll take a cup of kindness yet
for the sake of auld lang syne!

This Scottish folk song is, here in Europe and especially up north, regarded as a drinking song. A cozy pub or Kellerkneipe, with a table or a bar full of friends and a stein of beer before every friend, is what immediately comes to one's mind's eye.
To a Japanese listener, however, the same tune conjures either the New Year's broadcast on TV, graduations at either level of the school system, or shops and restaurants closing for the night (the tune replacing the background music to usher customers out). But not only the context has changed - the lyrics themselves are starkly different.
In the Taisho era, Auld Lang Syne was translated with completely different lyrics (at least literally, the metaphorical meaning being similar) into Japanese as Hotaru no hikari (蛍の光, The Light of Fireflies):

(STANZA)
蛍の光、
窓の雪、
書読む月日、
重ねつゝ。
Hotaru no hikari,
mado no yuki,
fumi yomu tsukihi
kasane tsutsu.

(REFRAIN)
何時しか年も、
すぎの戸を、
開けてぞ今朝は、
別れ行く。
Itsushika toshi mo,
sugi no to wo,
aketezo kesa wa
wakare yuku.

Which, translated into English to render the lyrics singable to the tune (this is my own translation), would sound like this:

(STANZA)
The light of fireflies, the snow
falls past a windowpane...
So many days and nights thus spent
reading come shine or rain...

(REFRAIN):
The years went by, meanwhile,
the years went by...
This morn we part at break of day,
after all the years gone by...

It's easy to see why it's regarded as a song about leave-taking (and thus played at such convenient scenarios, like graduations or New Year's Eve TV shows), instead of reminiscence like the source text.

Translation of a text that is sung in vocal music for the purpose of singing in another language—sometimes called "singing translation"—is closely linked to translation of poetry because most vocal music, at least in the Western tradition, is set to verse, especially verse in regular patterns with rhyme. 
Translation of sung texts is generally much more restrictive than translation of poetry, because in the former there is little or no freedom to choose between a versified translation and a translation that dispenses with verse structure. One might modify or omit rhyme in a singing translation, but the assignment of syllables to specific notes in the original musical setting places great challenges on the translator. The process is almost like strict verse translation because of the need to stick as closely as possible to the original prosody of the sung melodic line.

Other considerations in writing a singing translation include repetition of words and phrases, the placement of rests and/or punctuation, the quality of vowels sung on high notes, and rhythmic features of the vocal line that may be more natural to the original language than to the target language. A sung translation may be considerably or completely different from the original, thus resulting in a contrafactum.

Interesting word, "contrafactum." It's in Latin, second declension neuter; one contrafactum, two contrafacta. Coincidentally, and you may have spotted the family resemblance, it's a cognate of our English "counterfeit."

Contrafacta are different lyrics written to be sung to already existing tunes. You read any of the filks -about Westeros or any other fandoms-, for instance on this blog (Tywin of the Lannisters being the latest, am I right?) and get the idea, because filk songs are contrafacta by another name.

I mean, filk songs are contrafacta. The Mad Hatter's Little Bat is a contrafactum, sung to a classic French eighteenth-century tune mostly known as Little Star (and it can also be sung to Mozart's Little Star variations; wouldn't putting Carroll's Hatta and Amadeus in the same song cover be an instant piece of art?), and countless other contrafacta can be found across Carroll's Alice (The Little Crocodile, Father William, The Voice of the Lobster...).

A contrafactum happens when a rewriter in a target language takes the tune into account much more than the lyrics. This would be the case when the tune is the most important part of the package. Not translation proper in the linguistic sense, this is nevertheless a translational action: a result of importation of musico-verbal material between languages and cultures (and again, Auld Lang Syne / 蛍の光 may be a perfect example). A totally rewritten set of lyrics in a target language may contain only a single word, phrase, image, or dramatic element taken from the source lyrics. Also, the original lyrics (and singing performance) may influence the translator's impression of the melody, and thus, the production of the new lyrics. If these new lyrics allow the song, as a cultural artifact, to cross linguistic borders, the practice can be seen as translational action. For example, the impact of 蛍の光 in Japanese culture as a leave-taking song (at graduations, on New Year's TV, in shops and restaurants about to close for the night).

Joaquín Sabina's Mil maneras de olvidar a un chulo, based upon 50 Ways to Leave Your Lover, is not a contrafactum; the lyrics are more or less true to the original, but the tune is slightly different -being a musical variation on the original-. Still, the different tune and lyrics full of Spanish local colour make it an interesting adaptation, changing the song from US to Spanish culture with a different aesthetic, in the process changing the whole song (tune AND lyrics) from lethargic blues to lively, savvy flamenco. It's not a contrafactum, but still one of those translated songs whose target lyrics surpass the source lyrics.

Another of those translated songs whose target lyrics surpass the source lyrics would be Jag vill se schack. Comparing it to The Arbiter and preferring the Swedish version is something that, like when it comes to Mil maneras surpassing 50 Ways, is something that leads to the fact that I am always short of words for praising the target lyrics. It is NOT a contrafactum, but a singable translation that improves the original.

A contrafactum would be Var beredd, or Komm liebes Becherlein, or Alices snaps by Cornelis Vreeswijk (a song about a drunken dysfunctional family during a crawfish party, set to the heartwarming La chanson pour l'Auvergnat), or any of my filk lyrics (What's your name? TYWIN OF THE LANNISTERS!). Or 蛍の光 .

Translator Stanislav Korotygin also emphasized the creative joy of bringing this madcap talk into Russian, but admits that translating lyrics is alway a difficult balancing act. “It’s like searching for the best path through the forest which must satisfy several conflicting criteria: it must be the shortest, the nicest and the safest. And you have to meet the wolf on the way,” he jokes. “You start thinking like a poet or songwriter.”

And to Mile Živković, the number of syllables proved to be the biggest challenge in the Serbian translation. “It required me to compress everything so that I could imagine singing it in Serbian,” he says. “Initially, I attempted to make the entire song rhyme, but it proved virtually impossible with the line length.”