Board Thread:Consensus Track/@comment-3279282-20150712220400/@comment-945885-20150718110454

Viz uses "Sage of Six Paths" for the English manga. I don't recall offhand what the subs use.

I haven't seen enough of the dub to know what they use, but I'd assume they use "Sage of the Six Paths," since it would need to match the mouth movements of "Rikudō Sennin," which is also five syllables.