1. The translators don't understand Hebrew. This is a fairly important thing for someone to understand, if you're going to do a translation. An example: Isaiah 9:3 NIV:
You have enlarged the nation
and increased their joy;
they rejoice before you
as people rejoice at the harvest,
as warriors rejoice
when dividing the plunder.
Look at the second line. The Hebrew word for "not" is in that line in all manuscripts, and can be translated, e.g.
Isaiah 9:3 KJV
3 Thou hast multiplied the nation, and not increased the joy: they joy before thee according to the joy in harvest, and as men rejoice when they divide the spoil.
OK, the "not" here makes it important to figure out why it is there, and maybe the NIV translation is just a "kiddy" translation for those who can't take time to figure things out. OK for kids, but adults are supposed to take the time to understand things.
My second problem is that the translators don't bother to pick good manuscripts to translate from, picking instead ones with obvious errors:
1 The beginning of the good news about Jesus the Messiah,[a] the Son of God,[b] 2 as it is written in Isaiah the prophet:
“I will send my messenger ahead of you,
who will prepare your way”[c]—
Mark 1:1 Or Jesus Christ. Messiah (Hebrew) and Christ (Greek) both mean Anointed One.
Mark 1:1 Some manuscripts do not have the Son of God.
Mark 1:2 Mal. 3:1
The reason for the footnoting is that Isaiah 40:3 says:
3 The voice of him that crieth in the wilderness, Prepare ye the way of the Lord, make straight in the desert a highway for our God.
While Malachi 3:1 says:
Behold, I will send my messenger, and he shall prepare the way before me: and the Lord, whom ye seek, shall suddenly come to his temple, even the messenger of the covenant, whom ye delight in: behold, he shall come, saith the LORD of hosts.
Only a few non-Christian compilations make the error of including Malachi in Isaiah. The other 85% of the manuscripts say "prophets", as reflected, once again, in the KJV:
1 The beginning of the gospel of Jesus Christ, the Son of God;
2 As it is written in the prophets, Behold, I send my messenger before thy face, which shall prepare thy way before thee.
Why ignore the majority of manuscripts so that you can introduce an error, and then point it out in a footnote? It's not ethical. It's not right.
Finally, there's the lazy approach to translation: paraphrasing some other translation, and getting it wrong. Example:
King James Version (KJV)
17 Woe to the idol shepherd that leaveth the flock! the sword shall be upon his arm, and upon his right eye: his arm shall be clean dried up, and his right eye shall be utterly darkened.
Okay, a prophecy of some sort. Not easy to understand. But the NIV makes a total hash of it:
New International Version (NIV)
17 “Woe to the worthless shepherd,
who deserts the flock!
May the sword strike his arm and his right eye!
May his arm be completely withered,
his right eye totally blinded!”
"worthless" is not a synonym for "idol" -- it leads me to believe someone read the translated passage aloud, and it "idol" became "idle", and the paraphrase went on from there. So lazy translation hits in the old testament again. Given the number of translations that pick this up, it appears to be a common way to translate without having to learn Hebrew (and there's a pun in there between "eleel" and "heylale'", for fans of Isaiah 14:12). Gail Riplinger is famous for warning that lexicons tend to pick up the biases of translators over time, and therefore become worse over time. Possibly that's another explanation.
There are people who have studied this in more depth: Look What's Missing, some of whom appear to have a bias for other translations: The NIV Reconsidered : A Fresh Look at a Popular Translation is from one of the translators of the NKJV. I find his appendix on the greek text of the new testament interesting, and quite enlightening. It led me to do further research with Ancient Word of God: KJV Only or Not?, which had some interesting perspectives. The bible in English is hard simply because a new translation comes out about every six months: it is interesting to me that they all compare themselves to the KJV. Something like Spanish bibles do with Biblia Letra Grande RV 1909 (Spanish Edition)
, or Italian bibles do with the Italian Pocket Bible - La Sacra Bibbia La Nuova Diodati / Pocket Size Protestant Bible in Italian Language / The Bridge - Great for Students and people on the go / C03SE or French bibles do with the Olivetan. For my purposes, probably better to stick to the KJV, with its extensive system of commentaries and helps.