Raymond wrote:

> I don't know - only Andrew can answer that one.  But one must remember, I
> think, that Brithenig - for all its apparent Welshness - is a Romancelang.
> I guess that since no Romancelang exhibits umlaut, then the i-umlaut
> plurals seemed out of keeping - tho I see no reason why it might not have
> developed if Brithenig has such a strong Brittonic substrate influence.

In many galloitalic dialects vowels undergo umlaut processes:

southern Lombard: cavell  /ka'vEl/ > pl. cavij /ka'vij/

Bolognese is particularly rich in metaphonic plurals:

sacc 'dry' /sak/ > pl. scc /sek/
dnt 'tooth' /d&nt/ > pl. dnt /dent/
bind 'blond' /bjAnd/ > pl. bind /bjond/
vul 'flight' /vAUl/ > pl. vl /vu:l/
vaider 'glass' /vajder/ > pl. vder /vi:der/
cid 'nail' /tSOd/ > pl. cid /tSu:d/
strlg 'wizard' /strOlg/ > pl. strlg /strulg/.