All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction,
for instruction in righteousness,that the man of God may be complete, thoroughly equipped for every good work. - 2 Timothy 3:16-17
http://www.biblegateway.com/passage/?search=2Timothy3:16-17&version=NKJV
Jesus said to him, “I am the way,
the truth, and the life. No one comes to the Father except through Me. - John 14:6
http://www.biblegateway.com/passage/?search=John14:6&version=NKJV
That's just two verses out of the Bible.
And then there's the extra-Biblical evidence for the truthfulness of the Bible.
Much of the Bible is written not in the form of a philosophy book or theology book, but a history book (consider Luke 3:1-2). The Bible presents not a mystical message and not a contradictory message of feelings and emotions that sometimes tends to contradict or some kind of eastern mysticism like Hinduism where their ideas so often contradict. The bible on the other hand is a history book claiming that actual events happened in history and that these prove the story and the message of the Bible, and therefore if these events did not happen, we should discount the message of the Bible. But on the other hand, if the events actually occurred then at the very least we should take seriously the message of the Bible.
In other words, if there's evidence that the storyes in the Bible really took place, then perhaps the moral of the story is true also.
If we can show one story of the Bible to be true, and that's all, then we can say the Bible has some truth, but on average it's not reliable, so you can take or leave it's moral message.
But there are many, many stories in the Bible, and all the greatest stories of the Bible have evidence that remains to this day showing the story to be true. If all the stories are true, then there is overwhelming evidence that the message of the bible is true.
That's the difference between the Bible and other religious books that are not historical. You don't have that test of history and evidence to apply to the other books. But even books that are based on the Bible, such as the Quran (which refers frequently to the Bible) and the Book of Mormon, which attempts to copy the style of the Bible as a history book, cannot truly hold up to scrutiny. Let's take the Book of Mormon for example, which makes historical claims that cannot be verified, and in fact have proven to be completely false. The major historical claim of the Book of Mormon is that the American Indians are descendants of the Jews, yet not their language, their genetics, their culture, their diet, their religious views, their architecture, the tools that they used, nothing supports that claim, so we take the Book of Mormon and we say, "This book is not true." It's main historical argument is not true, therefore it's message is highly suspect. The historical message is corrupt and the spiritual message is corrupt, whereas the Bible on the other hand states throughout that there is one God that we worship.
So our Bible's historical claims gives us a context in which we can begin to study, test it, look at the evidence, and to reason, as God says "Let us reason together."
There is no presupposition required. Many Christians say one has to presuppose that the Bible is true. We say no, you can just look at the evidence. Christians who say, "well, you just have to have faith," (presuppositional movement) forget that faith is the evidence of things not seen.
If a book's historical claims are inaccurate, then it is most likely unreliable when it comes to moral teachings.
On the other hand, if a book's historical claims are accurate, then its moral teachings will most likely be of value.
Yes, translations introduce inaccuracies in spelling and grammar, and since the Bible has been translated from Hebrew and Greek into English, there is the possibility of introducing errors into the text. However, even though there are errors that, in spite of the careful transcription of the texts throughout the centuries, have made it into the text, the errors are usually so minor that they don't change the meaning of the surrounding text, and the overarching message of the Bible remains the same. Or what, do you think that the God of the universe couldn't write a book and have it survive translation? (Oh, and lets not forget those oh so important original manuscripts, like the Dead Sea Scrolls, which we can use to compare between the originals and our modern texts, and see that the message is the same.
The claim that the Bible is true comes from it's historical claims.
I addressed this above.