He left Kernari pretty young so you think he’d just talk like his adoptive parents on Ferrix. But everyone on Ferrix has a British accent (well except Bix but idk maybe her family immigrated there later in her life).
(And yes I know the real reason is Diego Luna is Mexican, but I’m high an felt like being a pedantic nerd)
(And yes I know Fiona Shaw is Irish)
Most actors are meant to be speaking galactic basic (which we translate into English or whatever the dub is in non English countries) it may be that Kernari and Basic are more similar than it appears to us and gave him an accent. He also did time in juvenile prison and in a paramilitary unit, so he might have picked it up like the person who brings a a slight accent back from studying overseas.