i'm satisfied with the current state of the page. i think "he/him (primarily)[1][2] they/them (once)[3]" provides all the information a reader needs and it's the kind of thing that could be brought to other characters if we have a similar situation.
as for the jp translation — it matters for a discussion of ralsei's gender, but not the pronoun parameter in the infobox. i would also not worry about us having a hollow knight wiki level situation. yes that was "not using they/them because of translations," but it was also combined with "admins not using they/them off of information that people were legally not allowed to see." since that last part isn't remotely true for deltarune i think we're good.