Craig4
Penultimate Amazing
I apologize (perhaps you should, too--for character assassination).
In Joseph Smith's day, spelling, many definitions, and punctuation were not standardized. In fact, work on an acceptable dictionary of the English language, The Oxford English Dictionary, was not even started until 1857, under the direction of Prof. James Murray (he died before it was completed, some four decades later). Today, as you may know, the "Oxford" is the gold standard of English language dictionaries.
In light of the foregoing, your reproduction of the original introduction is irrelevant. Why? Because as later editions of the BoM were published, editors changed the introduction to clarify Joseph Smith's intended meaning. They could clearly see (as could virtually anyone) that the last sentence was meant to summarize the entire introduction, not merely the Book of Ether. Common sense and context told them that. Why would Joseph Smith summarize only the Book of Ether in his introduction to the entire book? That makes no sense.
There are, in fact, nine em dashes (1979 triple combination), and they are not functionally limited to signifying a conclusion. Em dashes are used to indicate a break or change in thought, an unfinished sentence, and, yes, to set off summaries or definitions. (Geraldine Woods, Webster's New World Punctuation: Simplified and Applied, p. 114; Wikipedia, "Dash," "em dash)
Excuse me, but you err. You fail to recognize the non-standardization of punctuation in Joseph Smith's day (and for years thereafter), but more tellingly you cannot explain why the previous eight em dashes fail to yield to new paragraphs.
I'll be charitable: Consider the possibility that you may be in over your head.
Are you seriously suggesting that a translation error accounts for the claim that there was barley in the pre-Colombian Americas? I'll clear that one up. According to both the "American Frugal Housewife" and "Virginia Housewife" cookbooks, both published well before the first English dictionary the words barley and corn both appear (though I corn is sometimes spelled with a K).