Possibly this one.

"All right, I've been told some very contradictory things about you. The local custom is to nod your head like this for 'yes' and shake it like this for 'no'. Do you understand me?"

Nod!

"Are you sometimes unable to speak?"

"No, I can talk, just not your language."

"Did you pray for the Precursors to give us this food?"

"Precursors??"

He smiles predatorily. "Some people tell our creators about their problems in the hope that our creators will hear and take pity on them. But not you, I take it. Did you teleport here?"

...will this guy shake his hand if he holds it out.

Sure, though by default he'll do it with gloves on.

If gloves made touch range spells impossible then operating at the Worldwound in winter would be nigh-impossible!

"Share Language."

Erol gets everyone's attention and, as though this makes perfect sense, tells them he perceives himself to miraculously speak a new language and is going to tell their guest to clap his hands three times in that language as a test. And then he does that.

"That would also have worked before when I just had Comprehend Languages up," Blai remarks, clapping thrice.

"Assume I know nothing about your powers and explain them from the beginning."

"I am a cleric of Iomedae, Lawful Good goddess of defeating evil. She grants me a new complement of spells within the limits of what clerics, generally, can do, and within the limits of my personal ability, every morning at sunrise; I am powerful enough to cast spells up to third circle, and spells in general range from zeroth to ninth circle. Comprehend Languages lasts a bit less than an hour, Share Language all day; I prepared more than one Comprehend Languages but only one Share Language this morning. I can also heal, it's a primary capacity of clerics, either in a burst or with touch-range individual spells."

It's the healing that decides him.

"You are in Haven City. Haven City is besieged by metal heads - creatures of dark eco, who hunt and kill and destroy all that they can find. They have nearly ended civilization on this continent already. There is nowhere we can fall back to if they breach the wall - nowhere we knew of before you appeared. If you're going to vanish as you appeared, let me round up some civilians for you to take with you - otherwise, tell me more about your healing."