Dec 21 2019, 12:00pm
Well we can look at it from various angles, like we can say from in-universe perspective the style of English which is used as a stand in, or translation from westron or common tongue is used to differentiate somewhat person's background, look at speech pattern of gondorians, even simple soldiers like Ingold:
‘Yea truly, we know you, Mithrandir,’ said the leader of the men, ‘and you know the pass-words of the Seven Gates and are free to go forward. But we do not know your companion. What is he? A dwarf out of the mountains in the North? We wish for no strangers in the land at this time, unless they be mighty men of arms in whose faith and help we can trust.’
And it's noted in-universe that Gondorians used a particular speech style, and as seen in our perspective as of readers it is a bit more antiquated a bit more high style English with more archaisms:
In the days of the Númenórean kings this ennobled Westron speech spread far and wide, even among their enemies; and it became used more and more by the Dúnedain themselves, so that at the time of the War of the Ring the Elven-tongue was known to only a small part of the peoples of Gondor, and spoken daily by fewer. These dwelt mostly in Minas Tirith and the townlands adjacent, and in the land of the tributary princes of Dol Amroth. [..] in Gondor whence it came the Westron kept still a more gracious and antique style.
The Return of the King, LoTR Appendix F, The Languages and Peoples of the Third Age: Of Men
'Gracious and antique style' this is what is described as in appendices. Even Frodo notes when meeting Gondorians in story their speech pattern:
[Mablung and Damrod] spoke together in soft voices, at first using the Common Speech, but after the manner of older days, and then changing to another language of their own.
Common Speech after the manner of older days. Hobbits have their own more casual style (and apparently as Beregond notes they have 'strange accent' to a Gondorian, but he also points they too can be 'fair spoken') and even Orcs have their own style of sorts:
'Hullo, Pippin!' he said. 'So you've come on this little expedition, too? Where do we get bed and breakfast?'
'Now then!' said Uglúk. 'None of that! Hold your tongues. No talk to one another. Any trouble will be reported at the other end, and He'll know how to pay you. You'll get bed and breakfast all right: more than you can stomach.'
Orcs in Tolkien works actually don't particularly sound cockney-ish at all (that would be more part of Troll's speech patterns), in fact various Orcs speak quite eloquently. Like good old Grishnakh:
'Well, my little ones!' said Grishnákh in a soft whisper. 'Enjoying your nice rest? Or not? A little awkwardly placed, perhaps: swords and whips on one side, and nasty spears on the other! Little people should not meddle _in affairs that are too big for them.' His fingers continued to grope. There was a light like a pale but hot fire behind his eyes.
The thought came suddenly into Pippin's mind, as if caught direct from the urgent thought of his enemy: 'Grishnákh knows about the Ring! He's looking for it, while Uglúk is busy: he probably wants it for himself.' Cold fear was in Pippin's heart, yet at the same time he was wondering what use he could make of Grishnákh's desire.
'I don't think you will find it that way,' he whispered. 'It isn't easy to find.'
'Find it?' said Grishnákh: his fingers stopped crawling and gripped Pippin's shoulder. 'Find what? What are you talking about, little one?'. For a moment Pippin was silent. Then suddenly in the darkness he made a noise in his throat: gollum, gollum. 'Nothing, my precious,' he added.
The hobbits felt Grishnákh's fingers twitch. 'O ho!' hissed the goblin softly. 'That's what he means, is it? O ho! Very ve-ry dangerous, my little ones.'
'Perhaps,' said Merry, now alert and aware of Pippin's guess. 'Perhaps; and not only for us. Still you know your own business best. Do you want it, or not? And what would you give for it?'
'Do I want it? Do I want it?' said Grishnákh, as if puzzled; but his arms were trembling. 'What would I give for it? What do you mean?'
'We mean,' said Pippin, choosing his words carefully, 'that it's no good groping in the dark. We could save you time and trouble. But you must untie our legs first, or we'll do nothing, and say nothing.'
'My dear tender little fools,' hissed Grishnákh, 'everything you have, and everything you know, will be got out of you in due time: everything! You'll wish there was more that you could tell to satisfy the Questioner, indeed you will: quite soon. We shan't hurry the enquiry. Oh dear no! What do you think you've been kept alive for? My dear little fellows, please believe me when I say that it was not out of kindness: that's not even one of Uglúk's faults.'
How this will be rendered in the show, no idea, though I expect that if the care even a little they should try to emulate Tolkien's use of language and better yet use actual lines he wrote like it was sometimes the case in Lotr films. Of course other languages like Adunaic or Sindarin, Quenya could appear in some capacity. What sort of accent the English speaking actors should use I've no clue, it will probably come out in terms of how they will try to stylize this entire show, what sort of point of reference they will take. Still it should be that Numenoreans and Elves when speaking in common tongue of sorts whether we accept it as sort of translated elvish or native numenorean, it should seem more high style, (or as Tolkien would write 'lofty' :)) to make them seem more educated, well spoken and eloquent. Second Age also sees the first emergence of actual Westron as in Common Speech that is the main language used in Third Age in communication between various people, how this detail will be addressed is yet to be seen (westron arises in time of numenorean colonization, with the steady use of native Adunaic more, while the earlier Numenoreans used more often elven tongues, which in the end made them able to communicate with Elves on their terms).