Some critics argue that the insertion of "Red" in 2 Nephi 19:1, wherein the Book of Mormon reads "Read sea" as opposed to simply "sea" per Isa 9:1 is an error. On an old page from 1999 on the then-FAIRLDS Website, Ben McGuire offered the following comments:
First, here is the complete text of the King James Version:
Nevertheless the dimness shall not be such as was in her vexation, when at the first he lightly afflicted the land of Zebulun and the land of Naphtali, and afterward did more grievously afflict her by the way of the sea, beyond Jordan, in Galilee of the nations.
There are several aspects of this passage that make it naturally difficult. The correct translation is really by no means clear. Many modern translations, like the NSRV, contrast a former time of contempt and affliction with a latter period of glory. It is a fact though, that both verb forms render a past tense, and the second could just as easily be translated 'made severe' - i.e. "in the latter time he treated harshly the way of the sea." So, the KJV may not be that far off track. I do agree though, that it is not the usual translation of kabed, but, it is a credible reading.
The next issue with the text is that of time. What events do the verse describe? It is generally thought that the first line of verse 1 represents two invasions in either of two situations. First, it could be an invasion by Tiglathpileser (734-732) and an invasion by Shalmaneser V. Or, second, it could be simply two different invasions by Tiglathpileser. In this case, the most probable reading of line two, is the near future liberation of the provinces, implying that the reading of the text should be a return to honor. On the other hand, this presents a small problem in that the 'way of the sea' is not coterminus with either of the tribes. The former one would be Pekah, the king who lost the land to Assyria, and the latter one would be Hoshea. This assessment is however determined largely by the proposal that the Assyrians reduce Israel to the small state of Ephraim in 734-732, an assumption that is far from certain.
Another possibility all together is that former could be Jereboam the II and the later would be Menahem. By the end of Menahem's reign, Israel had completely lost the 'way of the sea, beyond the Jordan, Galilee of the nations'. Hosea 1:5 looks forward to the loss of the area, and Isaiah 9:1 would then reflect that loss. This would again put both losses in the past tense, and reflect more closely the KJV as opposed to the NSRV translation. This interpretation does become a bit more problematic with the introduction of the sea as the Red Sea, which would mean reassessing the situation entirely. Something I am not really equipped to do personally.
As far as geographically locating the way of the sea, aside from the interpretational issues above, there is still the issue of which sea is meant. Remember that they are discussing Israel, and not Judah. The alleged route is anything but certain, and is not agreed upon even by a majority of scholars. Many place it along side one bank or the other of the Sea of Galilee, to make it contiguous with the tribes of Naphtali and Zebulon. It is fairly obvious that any proposed route along the Mediterranean coast would not be. And some have suggested that the statement is merely a prophetic shadowing of the Messianic King (just as the following verses are) and that it really makes reference to Jesus. As far as that goes, It would make even more sense, as Joseph and Mary, coming out of Egypt with Jesus, would likely have traveled up the trade routes from Egypt, coming along the way of the Red Sea.
All of this is of course immaterial. Nearly all of our information about the battles and political information of the time comes from the Bible. It is the primary source. For us to say is there any evidence to suggest that vexation came via the Red Sea, would presuppose that it would occur within the primary source material, which is largely restricted to the Bible. So, your second question really has no answer. Were the original text to contain the mention of the Red Sea, the understanding of the situation would likely change.
As far as mistranslation goes (and this is by far the most important of the questions to answer), I look at it in the following way. First an analogy: A few years back, a translation of the Dead Sea Scrolls Isaiah was released. It was nearly entirely word for word taken from the KJV with an occasional variant reading from the ASV. This was so, even when the texts have fairly questionable and incorrect readings. Why? The answer is obvious. Any translation that makes use of existing texts highlights the differences. That is, with tools easily available, anyone can look at the text and determine the differences between the Biblical text and the DSS text. The same is true of the Isaiah in the Book of Mormon. We can, by looking at the text, determine exactly what parts are different, and which are for the most part exactly the same. In a sense, this gives us the chance to completely reconstruct to some degree, the text that Nephi worked with on the Brass plates. If on the other hand, The Book of Mormon text were to have been written in language popular at the time, we would not have so much information about the text. In fact, we would be dealing with a completely different set of issues. So, whether the language is translated appropriately, or not in both editions, we can accept that, supply a more modern reading for the portions of the text which are identical, and yet still proceed to know exactly which parts of the two texts differ.
In summary, an understanding of 1 Nephi 19:1 and Isaiah 9:1 lies on the following points:
1) A correct translation of the Hebrew. (Both readings can be shown to be legitimate.)
and
2) A correct placement in the historical framework of Israel and Judah. A framework, which is given its general form from the Biblical text itself, creating a circular argument.
Based on my personal understanding of the text, the Book of Mormon Isaiah is written in a way that give us an understanding of the differences between the Biblical text and the Brass plates, which it does marvelously well. And second, any secondary details, which it adds, are more or less impossible to verify using contemporary literature (there is practically none) and like the current text, is assessed merely on its own merits. It does however, add some light to the prophetic nature of the following several verses, and perhaps could even be the source of the prophecy mentioned in Matthew 2:14, assuming that the text had remained faithfully preserved in some manuscript at that point in time.
For more on this issue, see: