JOEL - Joseph Smith read the Bible and knew it well enough to know that the word "Christ" was a title and not a last name. Jesus is called "the Christ" in about 20 places in the New Testament.
"Messiah" and "Christ" can be considered different, perhaps not in their definition, but in how, when, and where they are used. The word "Messiah" is the Hebrew term that was used in the Old Testament to describe the expected deliverer of the Jews. Later, the Greek form "Christ" was used to identify Jesus as the Messiah. Here is the scripture you refered to:

"For according to the words of the prophets, the Messiah cometh in six hundred years from the time that my father left Jerusalem; and according to the words of the prophets, and also the word of the angel of God, his name shall be Jesus Christ, the Son of God." (2nd Nephi 25:19)

The context of this scripture is a prophecy about the coming of Jesus, first in Jerusalem and again in the latter-days when God would restore His Gospel on the earth(see verse 17). So God revealed to the Book of Mormon prophets that in the future this Messiah would be known as the Greek name "Jesus Christ". Providing this name would be a way to help people in the future realize the fulfilment of the prophecies about His coming. And of course those prophesies were fulfilled when Jesus made His first appearance in Jerusalem(there are almost 200 instances in the New Testament where He is refered to as "Jesus Christ"); and on the western continent(3 Nep. 11:10); and again in these latter-days when He restored His gospel, being called "Jesus Christ" in all these times and places.
Actually the name "Jesus Christ" can be considered an abreviation for "Jesus the Christ" (See Matt. 16:20).

ROBERT - The Book of Abraham:

How come Hebrew appears in a translation of Egyptian? Additionally, it should be noted that Hebrew came into existance after the time of Abraham.

JOEL - In Genesis 14:12-13 Abraham is refered to as a Hebrew. We are not sure what language Abraham originally spoke(possibly a form of Aramic), but when he went south to Canaan(Gen. 12:5) he picked up the local Canaanite language which later became known as Hebrew. So it is not impossible that Joseph Smith was inspired to use a few Hebrew-like words and names in the translation of the Egyptian papyri in order to preserve Abraham's original intent.

ROBERT - Why does the Book of Abraham mention Chaldea? Chaldea did not exist in history until the 12th century B.C. and thus is an anachronism.

JOEL - The "Ur of the Chaldees", mentioned in Genesis 11:31 and Genesis 15:7, is an example of an updated, intentional anachronism by a later Hebrew scribe, as is normal in the transmission of ancient documents.
An intentional anachronism is done so that later readers will have a clearer idea of what is being said, or so they will not be confused by archaic terminology.
Abraham's hometown during his time there was called Kasdim but was much later called Ur of the Chaldees when the Chaldeans became a part of the Babylonian population.
When the Bible was translated by the Hebrew writers they knew that the place that use to be called Kasdim was now being called the Ur of the Chaldees and so used this name instead. When Joseph Smith translated the Book of Abraham he was inspired to do the same thing to keep it consistant with the Bible.