It is DEFINITELY rewritten with my own flavor. But I went out of my way to maintain the original sound and characterization of each of the main characters. All of the characters have a greater degree of depth and maturity than the original, but they still maintain their original identity. As I mentioned in the description, the greatest deviations were with Headmaster Cid and Seifer. Rinoa has also received a lot of attention, but that is primarily in terms of adding to her backstory and motivation, not her personality.
I do not speak Japanese, but I had originally attempted to use a number of 'more accurate' versions of the script for reference and inspiration. But everything I found was so strikingly similar to the original that I gave up on that very quickly.
The version we received was remarkably faithful as a translation. I would only argue that it was fairly poor as a localization.
And also, despite what you may have heard, the great Ted Woolsey did not actually appear to me in a vision, providing me with his own immaculate localization. That was a joke.