Poor translations of religious texts exist in every modern religion, but I don't feel that is a main driver for misunderstanding Islam. I think stereotypes and an ignorance of the religion are the main causes for misunderstandings. Grouping terrorist cells or factions into a religious group is reckless and misrepresents millions of people.
There are many different beliefs about Islam, Christianity and all of the major religions. There are different sects of Islam and different Christian churches with different interpretations of the Quran and the Bible. These differences are not the result of translating errors; they are just the result of the ambiguous and contradictory nature of the text of these holy books. You can find passages justifying anything in the Bible and the Quran, and you can also find passages that condemn anything.
There is always the chance of mistakes happening when things are translated, however, there is no way that the whole of the religion would have been changed from it's basic core values because of a mistake in translation. Not to mention I'm so sure that the time and effort it would take to translate a whole book would require more than one person to do the translation. If there were potential mistakes I'm sure the majority of them would have been caught by others.
There might be small errors in translation, but that doesn't stand for the large things that Islam is against. Islam is against allowing Christians to live in peace. Islam is against allowing Israel to exist. Little translation errors here and there are largely academic. They do not change the fundamentals of what the religion stands for.
Translation mistakes are called copyist errors. They involve typos, punctuation, transposition, syntax etc. This is part of textual criticism which studies how ancient documents were translated and how reliable they were to the originals But to suggest that major doctrinal changes that are consistent throughout the arc of the entire Qur'an to the extent that peace became violence? That is tantamount to suggesting that after reading the English version of Mein Kampf where Hitler wrote about Christ's unconditional love for humanity, then come to find out the German translator "made mistakes in translating" it