Like I said last time, I don’t think it’s a huge logical leap that, when they’re looking for a Sith artifact by tracking a known Sith assassin, they find what is clearly a Sith artifact (based on the Sith language written on it), and deduce that it’s relevant to their Sith-centric mission. And they’re desperate for clues anyway. To me, that makes a lot more sense than someone programming 3PO with an illegal Sith to English dictionary, but then programming him to also not actually be able to use it, or to input the coordinates into the navigation computer himself, or something. The former is a reasonable deduction that anyone would make, especially given that the new dialogue line implies a level of logical reasoning behind it; the latter actually makes no sense.
At that point they’re not looking for a Sith artifact or Sith language, they’re looking for a nebulous “clue that could lead to a Wayfinder”, so it is a huge leap to make, not a reasonable deduction, specially coming from 3PO. Nothing implies the dagger is related to the Wayfinder at all, the “clue” could’ve been anything, anywhere, a piece of paper or a holorecording, the serpent could’ve eaten it for all they know. So 3PO would just be making a baseless assumption and the rest of the gang would immediatly agree it’s the one thing they need without a second thought. It would actually make no sense and I can see it being torn to shreds on analysis threads like this one.
3PO is fluent in over six million forms of communication, but a law that forbids translation of the Sith language was hard-coded into his programing at some point, I don’t see how that’s so complicated. Saying 3PO could’ve said the relevant information without a direct translation, or just punched in the coordinates, are just nitpicks, as there’s no specifics of how 3PO’s programming works. We’re told that he is “mechanically incapable” of speaking translations stored in his “redacted memory”, so who’s to say he isn’t also “mechanically incapable” of doing or saying anything that would relay that information?