The subject you are inquiring after is called "Textual Criticism" and involves the detailed analysis of some 30,000 handwritten manuscripts going back to the 2nd Century AD in the case of the NT and to about 1 BC in the case of the OT.
As far as the OT is concerned manuscripts are available in Hebrew and a Greek translation called the Septuagint, which may in many places differ from the original Hebrew. The reasons behind this variation are complex and too detailed to go into here. As far as the Aramaic is concerned, there are no Aramaic manuscripts of the OT as such, apart from copies of what is called the Samaritan Pentateuch, but ancient commentaries of sections of OT are available but here too, there are slight variations with the Hebrew.
It appears that the OT canon remained in a state of flux for several centuries as different traditions of manuscript transmission were being effected. This state of OT variables is referred to as "precanonical fluidity" by several scholars. This fluidity is not just a matter of different text forms but aslo of a plurality of what are called "redactional traditions" which caused various textual types to be heavily edited as well as transmitted. This may account for differences not only between the Hebrew and the Greek, but between the various Hebrew manuscripts as well.
The Hebrew text that we now have and which is called the Standardized Masoretic Text is a development of the Aleppo Codex which first appeared in completed form in 896 AD and was edited by one Moshe ben Asher. The printed edition of this text is called the Leningrad Codex and forms the basis of all translations that are currently being done on the basis of the Hebrew OT, and is now the standardized text from which comparisons are made with the Greek text. Despite the variables, there is a remarkable symmetry in the flow of the text and we are assured that no doctrinal intrusion was undertaken to blunt the integrity of the original writings.
As far as the NT is concerned, it was obvious right from the start that the early church took its evangelizing responsibilites seriously and almost from the start undertook to transmit the message of the NT into various languages. Probaly the first language that the NT was translated into from the original Greek, was Latin which was first begun in the 2nd Century AD. There are, again several editions of these Latin versions which are collectively called the Old Latin to contrast them with the lated single edition which attempted to harmonize the variants in the Latin. This edition of the Old Latin texts was called the Latin Vulgate, and was the first textual example of harmonizing a text in any language. This was first published in 386 AD and with the course of time itself became divergent since we have at present some 8,000 Latin manuscripts of the Vulgate all with their variations. Again, attempts were made to standardize the text, and the edition we now have was that made in 1592, and this "Clementine" edition of the Vulgate has been the standard of the RC Church. The name came from Pope Clement the 8th under whose supervision this task was undertaken.
Other important languages that became represented in translation from the early centuries of the church were Syriac, [or Aramaic] which dates from the 5th century, the Coptic from the same time, and the Gothic also from this period. Later manuscripts would come out in Armenian, Ethiopic, Georgian, and several in the ancient version of Arabic. It must be remembered that no manuscript was ever undertaken in Hebrew. The various Hebrew translations of portions of the NT that the Watchtower uses with such critical acclaim, are in fact printed editions of translations that date back to at least the 15th century when printing was first invented in the West.
The importance of these ancient translations is rich in tradition but limited in scope. None of the original manuscripts of these versions is extanct, and therefore existing manuscripts must be subjected to textual criticism to detirmine the original text as nearly as possible. In addition, in certain types of variants, some of these versions cannot reflect what the original Greek may have said.
For instance, Latin does not have the definite article, and the Syriac does not the syntactical ability to distinguish between the aorist and perfect tenses. However, having siad that, it must be admitted that the greatest benefit of versional evidence, that we get from these traditions, is that it can show that a particular reading was known in the place and time of the version's origin.
To get a better picture of this fascinatingly complex subject I would reccomend reading:
NT Textual Criticism A Concise Guide by David Alan Black.
Biblical Criticism: Historical, Literary, and Textual by Harrison, Waltke, Guthrie and Fee in the Contemporary Evangelical Perspective Series.
Introduction To NT Textual Criticism by J Greenlee
And related articles found in such Bible reserch volumes such as the Interpreter's Bible Dictionary, The International Standard Bible Encyclopedia, The Revised International Standard Encyclopedia. Some of these are available for free on the Net, others should be available in any good public library.
