Copying table of pronunciation:
|Phoneme in English||Phonetic in Brummie||Example|
Did you get it? English word "mouth" is usually pronounced as [aʊ], hence phoneme /aʊ/, which is what very many European or other Latin alphabet languages would spell as AU.
In Birmingham there are two pronunciations : [æʊ] and [æə]. The former might be spelled as EU, though that might (or instance in Classic Attic) have been more like [eʊ] in other languages using the spelling. But the second of these pronunciations is exactly what manuals of Old English (or Anglo-Saxon) describe the pronunciation of EA as having been.
If I try to learn Anglo-Saxon, I have to laboriously figure out how to pronounce EA. Bot Tolkien could have heard someone tell him "like mouth is pronounced in ..." (add name of village or city district where pronunciation was [æə]" and he certainly had been imitating the accent enough to get it right.
One more thing, this points to the successive pronunciations of MOUTH in Birmingham as having been successively [aʊ] > [æʊ] > [æə]. And that is probably how Common West Germanic AU became Anglo Saxon EA.
"Brummagem ... The word appeared in the Middle Ages as a variant on the older and coexisting form of Birmingham (spelled Bermingeham in the Domesday Book) and was in widespread use by the time of the Civil War. Brummagem (and historically also Bromichan, Bremicham and many similar variants, all essentially "Bromwich-ham") is the local name for the city of Birmingham, England, and the dialect associated with it (see, for example, Carl Chinn). It gave rise to the terms Brum (a shortened version of Brummagem) and Brummie (applied to inhabitants of the city, their accent and dialect, and frequently West Midlanders and their accents in general)."
And West Midlands is of course where Tolkien - about as good as you get on Anglo-Saxon linguistics - thought West Saxon traits were the purest, had best survived Norman invasion. Englishmen call a primary colour "red", historically "read"*, because they spoke Germanic with a Brummie accent.
A "Brummagem ware" might be** a shoddy imitation, but a Brummagem accent has a certain English brilliant originality to it.
How come I came across the word? Jess Phillips is in a Daily Mail article described as a Brummie.
Hans Georg Lundahl
St Andrea Corsini***
* As opposed to German rot from AU > O: before dentals, as opposed to Nordic Ö, probably through a modified Brummie : AU > ÆU > ÖU > Ö: . Update: sorry, not Nordic, but East Nordic. Icelandic has written AU pronounced as ÖU. ** Or might have formerly have been, back in days of Industrial Revolution of England. Before John Ruskin improved industrial products. *** Sancti Andreae Corsini, ex Ordine Carmelitarum, Episcopi Faesulani et Confessoris, cujus dies natalis agitur octavo Idus Januarii.