Social: There are two essential pieces of information. The first is that the former priests of Noah are made teachers "in every land which possessed" by the Lamanites, and the second is that the language of Nephi "began to be taught" to all Lamanites.
The first instruction is a presupposition to the second. The former priests were teachers, and therefore they taught the language. Certainly the priests of Noah would have been learned men, and therefore their appointment as teachers is not necessarily surprising. What is surprising is the assertion that it is the "language of Nephi" that is being taught. This second point requires some examination.
Let's begin with the facile assumption that the Lamanites and Nephites refer only to the lineal descendents of Lehi and that they never mixed with any other people. Both groups began by speaking the same language, and while 500 years is a long time, it is not long enough for complete unintelligibility between separated speakers of the same original language. If we begin with the assumption that no one is around but Lehi's direct descendants, then this statement is nonsensical.
When we take into account the proposed cultural milieu suggested in this commentary, we still have problems.
While we can easily see the original Lamanites losing their language, and the original Nephites eventually losing theirs in Zarahemla, neither of those cases explain what is happening in this verse.
According to the internal evidence examined, the "Lamanites" that we are dealing with are former "Nephites" who remained in the land of Nephi when Mosiah and his people escaped with their lives. The Zeniffites are able to return precisely because Zeniff knows the land and the language.
We have no indication in any of the record of the proceedings between Shemlon and Lehi-Nephi that indicates any problem in understanding each other. Since the king of the Lamanites referred to here is the king in Shemlon, and the priests of Noah were in Lehi-Nephi, that would seem to indicate an ability to communicate that precedes their joining with the Lamanites. What is going on?
The most likely explanation lies in the possible meaning of the word "language" as it is used in the Book of Mormon. While there are times when it certainly indicates the spoken word, there are other times when it is equally likely that "language" is used as a synonym for "culture." See the discussion following 1 Nephi 1:2-3 for a more complete analysis of this usage in the Book of Mormon.
If Mormon is using "language" as a synonym for "culture," then this passage becomes much clearer. The Amulonites are teaching those aspects of Nephite culture that would have given them their competitive advantage in the trading markets. Note that verse 7 explicitly ties the enrichment of the Lamanites to this teaching by the Amulonites, and very specifically mentions trade (though in a different way than suggested here).
I suggest that this is the meaning of the verse. The culture of the Nephites, those things that have in the past given them a trading edge (remembering how rapidly the early Nephites and the Zeniffites rose to riches). Among these cultural "improvements" was also writing, according to the assertion in verse 6.
“And Thus the Language of Nephi Began to Be Taught Among All the People of the Lamanites”
Historical: Verses 1-7 constitute an insertion by Mormon that gives an overview of the effect of the Amulonites on the Lamanites.
When viewed with an historian's eye, these verses are somewhat suspect as to their complete accuracy. The problems are:
What is going on in these verses? It is most likely that Mormon is indulging in the rather human assumption of the superiority of one's own culture. He supposes that Lamanite advances are directly related to the importation of Nephite information. This same tendency has overshadowed the earliest research into the history of the New World, when most of the native advances were assumed to be related to the importation of ideas and peoples from the Old World.
The Mormon community of writers have been equally as bold in proclaiming the Israelite origins of the American Indian, with equal error in overstepping the bounds of what the Book of Mormon claims for itself. Rather than an explanation of all Amerind peoples, the Book of Mormon deals with a smaller number of people in a limited geographic area (such is the assumption of this commentary).
The question remains open as to whether or not there were contacts between the Old World and the New:
For Mormons, the presence of some Israelites in the New World is a matter of faith. While the Book of Mormon is quite consistent in describing those Israelites as they participated in a Mesoamerican culture, it says nothing at all about the direction of influence of culture, whether the Israelites provided culture to the Mesoamericans or the Mesoamericans provided it to the Israelites.
Archaeology, on the other hand, is reasonably clear that the greatest transfer of culture was from the Mesoamericans to the Israelites, in that the Mesoamerican culture can be traced to times prior to Book of Mormon contact, and there are no obvious Israelite cultural influences in the Mesoamerican culture set.
Of course this does not suggest that the Israelites were not there, and some archaeologists would suggest. It merely states that the material culture of the Book of Mormon participated in the material culture of the Mesoamerican area, just as modern Mormons in every country participate in the material culture of their own lands, with homes, vehicles, and cooking utensils that look every bit the same as their neighbors.
This tendency, however, to see one's own culture as dominant, and therefore as the source for other cultures, is a very old one, and it appears that Mormon was no stranger to the sway of the idea.
What Mormon will present is an idea that most Lamanite advances were due to the Amulonite's teaching Nephite ways to the Lamanites. While certain teachings may indeed have been imported, the picture that Mormon gives of the renaissance of Lamanite culture after the importation of a few men well overstates the case as it can be reconstructed from the Book of Mormon text and the known archaeology of the area.
It may be reasonably asked upon what basis one may question the accuracy of anything in the Book of Mormon, since Joseph Smith called it the "most correct book."
Clearly the conception of "correctness" has much more to do with doctrinal purity than with the absence of error, as there have been numerous alterations for spelling and grammar in the text (the Book of Mormon Critical Text. FARMS 1987 contains most if not all of these alterations over time).
Since the "correctness" or the Book of Mormon does not preclude its essential existence as the result of human labor, with the potential imperfections of human nature, we may turn to the Bible as a model for how humans have dealt with information about and from the divine. That text also shows its roots coming from particular places and times, and from the culture bound notions of its writers, inspired though they were.
Similarly, we may expect that the Book of Mormon is the result of humans who participate in, and absorb much of, their own cultures. In the ancient world, there is a nearly universal tendency to exalt one's own people over any and all others. When the Book of Mormon is seen as an ancient text, these touches of ancient humanity only serve to strengthen our understanding that the book was written by real people, in a real place, during real times.