@lds Maybe Indy met up with him and the others on location, near the hidden temple?
Honestly, in terms of plot and technical specifics, I think we have to give the whole opening segment a big pass, as it plays pretty fast and loose with the rules in order to set the stage, give us the big intro to "this is like old movie serials, right?" thing.
Forrestal is one of the few who's ever made it this far, and Indy is only just now getting this far, probably from following Forrestal's notes or something, right? So no modern person has found this temple before, maybe a couple of years ago. Yet Alfred Molina points out that no one has come out of there alive. Well hell--either Forrestal or Indy could have just found Al in a bar somewhere and asked him about the temple, and he'd have led them right here! No need to piece together scraps of ancient maps or anything; Mr. Molina seems to *know* this place*, and perhaps even have led others here before. Why isn't he the one walking in front, if he already knows where he's going?
But the accent thing--if I'm even hearing it, I'm still not 100% convinced I'm not imagining it--that's down to the actor or editing/ADR.