What @brightlydoesit said, except to correct the ‘modern’ characterisation of the Demonic version of the Word; all languages are equally modern if they are spoken in the present, even if they contain more or less variants of their original source.
That aside, GREAT POST OP. If we do consider Angelic Word and Demonic Word to be different dialects of an original shared language, then 6000 years (in human languages) is the approx age of the entire Indo-European language family (~100 languages), or more impressively, the ~1200 language Austronesian language family of the Pacific. You can get remarkable diversity in just a few centuries: 6000 years from a common ancestor gives you languages as diverse as Hindi, Irish, and Albanian.
But human languages evolve in communities of speakers, of course. What do we know about the communities of A-Word and D-Word? Not to get too hairsplittingly theological but don’t we think that a third of the angels got chucked out to become demons, and there’s at least ‘millions’? So that was a very large original speech community, probably with internal variation in the range of contemporary global English or global Spanish variation. In that context there would have been some sort of God’s Tongue official variety for business as well, just to keep the bureaucracy of Heaven running (do not @ me if you don’t enjoy this sociolinguistic take on a fictional loosely-Christian Heaven).
So let’s imagine that Aziraphale and Crowley were (best case scenario) both highly competent speakers of the official God’s Tongue. In my mind it had delightful things like semantic marking through auditory harmonics, emotional stance obligatory in grammar, clicks, evidentiality, complex noun classes, dual-person pronouns, a base six number system and lots of other cool stuff that only occasionally turns up in human languages. They possibly also spoke a variant dialect with their mates, as we all do, full of age-graded vocabulary and constructions and the policing of other angels accents as ‘funny’. I don’t spend a great deal of time thinking about pre-Fall Heaven, so, YMMV there. But to characterise how Crowley and Aziraphale speak now we then need to answer the following:
Who interacts more with their original speech community (bearing in mind this too will evolve) over the millennia? My money is on Crowley here, but given they’re both not keen on their fellow angels and demons, the extent to which any post-Eden language interaction affects their contemporary varieties is probably quite minimal.
Where (and therefore with which human speech communities) do they spend large portions of time interacting with humans? At least 4000 years seem to have been spent in the vicinity of Afro-Asiatic languages (Akkadian, Aramaic, etc) if we take the view that Aziraphale and Crowley hung around in places where people believed in their pre-/Abrahamic kind of supernatural being. So the bulk of influence will be from languages whose present day descendants are thinks like Arabic and Hebrew. Then whack in Ancient Greek, Latin, Ptolemaic Egyptian and other big state languages as a secondary layer of influence. That leaves the last two millennia as a hodge-podge of Indo-European influence, with Textual evidence for French, Spanish and a number of centuries of English.
What do we know about how highly multilingual speakers speak? We know that people code-switch easily between varieties according to the social and interactional situation. The things we do with language are frickin’ amazing and smart; we switch for strategic reasons (social reasons for the most part) and we don’t often do it if we don’t think people will understand us or it will not be to our social advantage. and even if people have 4-5 languages in common they will usually only alternate between a max of three of them in any one conversational utterance. So would (for example) Crowley pepper a sentence with words from a load of different languages? Probably not, unless those particular words were ones that he and Aziraphale had conventionalised in their own idiolect (fancy word for a personal dialect). @brightlydoesit and I have this for a handful of Dutch and Maori and nonsense words that we sprinkle in our speech, but they’re ones that we’ve negotiated through use to be part of our shared vocab. Switching and mixing grammatical constructions is much less well-studied, but we’re also much more flexible in understanding things like subject and verb from context: ‘bookshop fire’ and ‘fire bookshop’ get the same message across.
What do you mean ‘sounds a bit like Welsh’? Are you one of those people who make fun of Welsh? No, I bloody love Welsh and feel daunted every time I try and think about learning it, because it has things like CONSONANT MUTATION which is just so groovy. In Planning Permission, Anathema thought that Word sounded like Welsh, because she has a limited frame of reference for other languages. But it would have sounded a bit like Welsh in the different prosody and word stress patterns.
Words and grammar are boring, what about accent and sign and pragmatics? Yes, you’re right, and OP @ineffableomensgo is totally on to something with their speculations on gaze and body language etc. Sign and gesture were likely part of the very early origin of language; no reason why that wouldn’t be different for other beings with some sort of material form. Pragmatics is the part of linguistics concerned with the contextual aspects of language – the social and behavioural functions of utterances in context. The classic example is what is meant by saying ‘It’s cold in here’ - is it an informational statement or a request to open the window, or leave? Frankly the entire GO fandom’s fic output is a pretty decent exploration of the pragmatic functions of sentences such as ‘you go too fast for me, Crowley’, so we’re all doing good on that.
Why did you not cite sources, @blythe-ly? I am lazy and I just spent the day citing sources for a living.
tl;dr ask me about evidentials, they are cool.
