Here’s what RogueLeader and I have got for Sith-3PO’s translation of the dagger:

We whisper to a darkened heart
Unveil the way with secret art
For faithful Sith whose hatred swells
Wayfinder, only this blade tells

The poetic form hopefully gives it a sense of ancientness and mysticism, while the information conveyed still explains to viewers how the dagger works.

The first line establishes the whispers, and that Rey will need to embrace the Dark Side to hear them. The second line explains what the whispers will tell her - they show the way forwards. The third line repeats and reinforces the core takeaway we want the audience to remember - the dagger requires Rey to use the Dark Side. But it also adds to that idea, giving a more specific instruction to her than vague “darkness” again - she has to use the hatred and anger that plagues her, which ties more closely into how the remainder of the story actually plays out. (I’m especially fond of how this line directly references the Emperor’s speech to Luke in ROTJ, where he literally says Luke’s hatred is swelling when he goads him to give into his anger and the Dark Side.) And finally, we had to have the line Rey repeats later in there, explaining that the blade specifically points to the Wayfinder.

I’ll do a test recording as 3PO tonight if I can; I’ll need someone else to add the audio effects he speaks with, though.