The gnoll is actually talking common to you as you can see by the lack of <braces> aroudn his speech.
"What would you need our surrender for? You want to become the new lords of the House of the Beast? I don't think so. The only thing you need is to ensure that no new threat to your beloved Kelmarane arises from this place."
"And that is what I'm offering you. You may pass through these halls unhindered further into the belly of the beast, so to speak, to remove what created this Carrion King. And with that, the threat that this place poses to your beloved home."