What's the meaning of "I think dead, too"?

Question

C-3PO and Poe finds a speeder in the caves:

C-3PO: Perhaps we will find the driver.

(BB-8 Chirps alien language)

Poe: Yep, BB-8, I think dead, too.

What's the meaning of "I think dead, too"?

Answer 1

It is a common trope in Star Wars that characters unnecessarily repeat what droids are saying, because while they in-universe understand what the droid said, we, the audience, don't. This is similar to how in many movies where a phone conversation is shown only from one character's perspective, the character repeats everything the other person is saying.

You can almost think of it like a puzzle, the dialog is designed to give us enough information to fill in the gaps.

So, in this case, we are meant to fill in the gaps in the dialog maybe something like this:

C-3PO: Perhaps we will find the driver.
BB-8: Probably dead.
Poe: Yep, BB-8, I think dead, too.

Answer 2

The official novelisation doesn't directly translate his Droidspeak, but we can certainly work out what he meant from the context.

“Perhaps we’ll find the driver,” C-3PO said.

BB-8 told C-3PO what he thought of that.

“Yeah, I think dead, too,” Poe said.

The Junior Novelisation also mentions BB8's snarky tone.

“Perhaps we’ll find the driver,” C-3PO said.

BB-8 trilled something snarky.

“Yep, BB-8, I think dead, too,” Poe said. Chewbacca barked in agreement.

With that in mind, it was almost certainly something sarcastic like "perhaps we'll find his body".

Answer 3

Speculative answer: this may be a callback to dialogue from The Last Jedi, the previous film. After the Raddus jumps to hyperspace, Poe and BB-8 have this exchange:

BB-8: [looks over at hallway, beeps]

POE: "Finn naked leaking bag"? What? Did you fry a chip?

[Poe looks over to see Finn walking around in a leaking bacta suit.]

Besides the humor of BB-8's strange claim turning out to be true, the implication of the phrasing here is that either a) Poe isn't 100% fluent in droidspeak, or b) BB-8's speech is telegraphic, and doesn't cleanly translate to "complete sentences".

In the scene in The Rise of Skywalker, since Poe is apparently quoting BB-8 to agree with him, it's possible that BB-8 literally said "I think dead", or at least that that's what Poe understood him to say.