I have been through Act 1 over a dozen times by now but I can not seem to figure out the timing to get these two conversations from Shen.
I assume that The Stranger happens some time after you bring the buy back form the crater (Yes I know whom he is already) but I have no idea what leads up to it specifically.
As for The World, no idea. Order in the list seems to imply it is some time after you take care of the Skeleton King but I have noticed the order in the list is not always chronological (Found this out with the books in Act 3 where one of them is among the last you collect).
If these should be separate questions let me know but I fear a question for every check box on these achievements.. I just can not figure these talking points out!