No problem. When I have time, I am always willing to answer questions like this.
What about the original first 116 pages that were lost/stolen? Why didn't Smith re-translate them.
The whole story is in D&C 10. It is much too long to paste here. The summary is that Joseph was ordered not to retranslate them to prevent somebody modifying and then presenting what they claimed to be the original 116 pages and claim that they were different, and therefore that Joseph was not a prophet.
One thing to keep in mind is that Joseph did not do a translation in the way that we think of it. Today we think of somebody taking a sentence, and then turning it into a sentence in the language desired.
What happened with Joseph was that he was given in his mind an impression of what was on the plates. He then took that impression and used his own words in english for what he saw.
In some cases, he was given a word-by-word translation. Other times he was told that, for example, the stuff in the King James version of Isaiah was close enough, so use that. And other times he was just given the thought and had to put it into words the best he could. This helps to explain some of the "modern" words found in the Book of Mormon. They are modern because those are the words that Joseph chose to use when conveying the thought he was given.
Much like I am doing now. I have a thought that I want to pass to you. I am trying to pick the words that best express it. If for some reason the computer lost what I wrote here, I would still have the same thought. However, I would likely use different words to express it.
And that might be the problem Joseph was facing. If he redid the 116 pages, it was likely that some words and phases would be different. And even if it wasn't, there was the fear mentioned above, that somebody would modify the original.
What language did Mormon speak, what was the book written in, and what is the oldest extant version/translation of the original?
I don't think we are told the language that Mormon spoke.
From the record, it would appear that at least five languages were spoken in the Book of Mormon. That of the Etherites. The original of the Nephites/Lamenites (describe by Nephi as "which consists of the learning of the Jews and the language of the Egyptians"). That of the people of Zarahemla ("their language had become corrupted; and they had brought no records with them; ... and Mosiah, nor the people of Mosiah, could understand them"). It appears that the Lamenites eventually spoke a different language than the Nephites ("the language of Nephi began to be taught among all the people of the Lamanites"). And it even appears that the Nephites had a different language than the original (King Benjamin, a Nephite, had three sons, "and he caused that they should be taught in all the language of his fathers").
Who knows what Mormon spoke. He lived near the end of the Book of Mormon history, and about 1000 years passed since the beginning of the Book of Mormon. Think of the changes in english in the last 1000 years.
As for the language on the plates, Mormon 9:32-34 says:
32 And now, behold, we have written this record according to our knowledge, in the characters which are called among us the reformed Egyptian, being handed down and altered by us, according to our manner of speech.
33 And if our plates had been sufficiently large we should have written in Hebrew; but the Hebrew hath been altered by us also; and if we could have written in Hebrew, behold, ye would have had no imperfection in our record.
34 But the Lord knoweth the things which we have written, and also that none other people knoweth our language; and because that none other people knoweth our language, therefore he hath prepared means for the interpretation thereof.
So the plates that Joseph Smith was looking at were written in what Mormon called reformed Egyptian.
Lastly, there are original copies of the first edition of the Book of Mormon available. I've even seen transcripts of it on the internet.