You can compare the King James and 24 other translations, most from the original Greek and Hebrew at this convenient website: http://biblehub.com/john/3-16.htm. While the choice of synonyms varies slightly, they generally match in meaning well enough to leave no doubt about who Jesus and his apostles were and what they did and said.
We also have the writings of the early church fathers, quoting those scriptures. Those quotes match the Bible we have today remarkably well and collectively they provide independent checks on almost all of it.
None of them leave any doubt about the fundamental message of Christianity.