Dead as a Doornail:
Marley was dead: to begin with. There is no doubt whatever about that. The register of his burial was signed by the clergyman, the clerk, the undertaker, and the chief mourner. Scrooge signed it: and Scrooge’s name was good upon ’Change, for anything he chose to put his hand to. Old Marley was as dead as a door-nail.
Mind! I don’t mean to say that I know, of my own knowledge, what there is particularly dead about a door-nail. I might have been inclined, myself, to regard a coffin-nail as the deadest piece of ironmongery in the trade. But the wisdom of our ancestors is in the simile; and my unhallowed hands shall not disturb it, or the Country’s done for. You will therefore permit me to repeat, emphatically, that Marley was as dead as a door-nail.
(A Christmas Carol, Stave One - Marley's Ghost, 1843)
Thus begins the opening paragraphs of the first chapter of Dicken's great Christmas classic, stating in typical elephantine if sarcastic manner, and hammering home rather Britishly that mortification of Jacob Marley, fraternal partner i business of Ebeneezer Scrooge.
The "doornail" shall play a pivotal role in this supernatural Christmas tale as Scrooge will encounter the spectre of Marley not once, but twice throughout the first chapter of the story- one to the point, manifesting his face in the form of a doorknocker - one related through the genus of wooden portals to doornail. Therefore, Jacob Marley is quite ghostly alive as a "doornail" - provided that one has some leeway- animated as he is from beyond the grave.
How then ought the translator handle a pun that literally ties into as a foreshadowing of Marley's later reappearance as the knocker of Scrooge's door?
You can't really alter it to a different object as such with a similar mortal wordplay, as the reference will then be lost completely. Doornails are by their very nature lifeless metal objects thus one could make the case that you could in fact preserve it as is and merely translate the the local word for something related to a door, but at the same time losing a familiar wordplay on a known aphorism for being completely dead - and instead strike the reader with a strange, at first glance, reference to bits of metal and the posthumous state of Mr. Jacob Marley.
Charles Dickens also presents his narrator in the same overly courteous and cautious tone as he always does, setting the mood for the rest of the story in its macabre humour, and in contrast to the later moralistic sombreness with added elements of existential horror.
Thus taking a look at the five translators and isolating the scope of the analysis to more accurate regard the "Old Marley was as dead as a door-nail" line:
Kusano Shibaji (1902):
Rou Maarei wa hikite no you ni shi kuchite ite.
"Old Marley was as rotten dead as a metal-ring-button ("door nail")."
Yaguchi Tatsu (1915):
Maaree roujin wa tokugi no you ni shinde shimatta.
Old-man Marley was as thoroughly dead as a door-nail.
Nakajima Kotou (1920):
De, Mârê roujin wa, mou iki no ne ga pittari to tomatte shimatta no desu.
"Therefore, old-man Marley's life had stopped all and truly of a sudden."
Hataya Masao (1925):
Maaree roujin wa tokugi no you ni shinde shimatta
"Old-man Marley was completely dead as a door-nail."
Morita Souhei (1929):
Rou Maarei wa to no byou no you ni shi ni hatete ita.
"Old Marley was perished and dead as the tack of a door."
Only Nakajima seems to disagree on Marley's terminal state, simply stating that that his "life has stopped", whereas the others in a resolve to find a fitting Japanese substitute go from a literal translation "door-nail" (hence my hyphening it, since there is apparently no word structure as such), "metal-ring button" which is then outfitted with the furigana/ruby for "knob/handle" (hikite); Morita resorts to "tack of a door", a more descriptive way of handling the state of Mr. Marley.
Kusano in particular strikes home that Marley is as "rotten dead" as a "(door)knob" and Morita makes it clear that Marley has "perished" and is "dead." Both stressing the inexorable status quo of Scrooge's friend - which won't hinder him in revisiting his business-partner.
I have to say that I like the vividness of the above two. Nakajima merely gave up on conveying the wordplay and just translating it straight up, without even trying.
“Bah!” said Scrooge, “Humbug!”
(A Christmas Carol, Stave One - Marley's Ghost, 1843)
"Fun, bakabakashii!" to, Sukuruuji ga iu.
"Hmph! How foolish!" said Scrooge.
"Baa!" Sukuruuji wa itta. "Kuso o kurae!"
"Bah!" said Scrooge. "What a load of nonsense!"
"Kuraboume!" to Sukuruuji ga iimashita.
"Damn absurd!" said Scrooge."
"Nanda! Kurabou na!" to, Sukuruudi wa itta.
"What! How absurd!" said Scrooge."
"Nani o, bakabakashii!" to Sukuruuji wa itta.
"What are you saying!? How idiotic!" said Scrooge."
"Bah, humbug" is here given renditions of being "foolish/idiotic", "absurb" or "utter nonsense", whereof the latter is very literally "eat shit," (糞を喰え, kuso o kurae, where it can also be translated in modern slang as "fuck off" or "to hell with it") which grants Scrooge a tone mostly in tune with his 2020 gritty BBC self, where "fucks" and "shits" are flung with extravagant Christmas charity. So on one hand there is similar wordings, albeit none quite captures the "humbug", though a case can be made for kurabou (translated here as "absurd(ity)" as a viable choice). Kuso o kurae on the other hand, a faecal imperative, if put into the hands of a translator more used to its modern meanings will turn Scrooge into a sulphuric character that would scarcely have made it off the printing press.
"Humbug" as a word means "trifle", "nonsense" or just "useless matter," hence the translation-choices of the above reflect how either idiotic or absurd Scrooge views the Christmas month.
Scrooge telling his nephew to "fuck off" would warrant much more than just a jovial "Christmas, a humbug, uncle?" and presumably not even the Ghosts would even be bothered with saving the old fucker.
There is no exact exemplar quote to derive this from since it is an ubiquitous term not only in the story, but also its very seasonal foundation.
The translators either opt for using the regular katakana version of the name of the holiday itself:
クリスマス - Kurisumasu - "Christmas"
Or, in more creative ways apply this word as a rubi for already existing kanji compounds expressing a similar idea, which what I shall be listing below, with the actual reading of the word, should it be read without the Kurisumasu furigana.
祝日 (shukujitsu, "national/public holiday")
This mostly appears in the name of the Ghosts themselves, whereas any reference to Christmas itself the loan word is used instead.
Yaguchi Tatsu, Nakajima Kotou and Hataya Masao:
They all use the loan word.
降誕祭 (koutansai, "The Nativity", lit. "Festival of the Regal Birth")
Other than this Morita also uses 聖降誕祭 (seikoutansai, "Holy Christmas", lit. "Holy Festival of the Regal Birth"), read as a regular word rather than with the loan-word reading Kurisumasui, and this is most often also used in conjunction with people's felicitations, thus "Merry Christmas" is rendered as "聖降誕祭でお目出とう (Seikoutansai de omedetou, lit. "An Auspicious Holy Festival of the Regal Birth [to you]").