It means that they have caused controversy by adding their opinions to the text they are translating rather than sticking to the literal meaning.

For example some biblical scholars changed the phrasing of parts of the Bible to suit their political agenda, the King James Bible for example is supposed to play down how bad it is to be a tyrant (I've not read it so I can't confirm this).

Wikipedia defines Controversy as:


  Controversy is a state of prolonged public dispute or debate, usually
  concerning a matter of opinion. The word was coined from the Latin
  controversia, as a composite of controversus – "turned in an opposite
  direction," from contra – "against" – and vertere – to turn, or versus
  (see verse), hence, "to turn against."


What does "to become controversial" mean?
I time-warped in Animal Crossing: New Leaf so I could get to the award ceremonies for the Bug-Off. I time-warped a year ahead, and now my hair's all messy. How can I put my hair back to normal?
