That's a little hard to quantify. Most of the "technical" or scientific terms they use don't differ a whole lot because they're referring to established concepts that have terms in English (or sometimes they're just using the English term in Japanese.) There are a few game-specific terms and names that we changed for several different reasons, such as: They sound silly in English, they rely on sounds/wordplay that doesn't work in English, they tie into the plot in ways that won't work (in English) unless we change them, etc. The stuff that diverges the most is probably the jokes, which frequently just don't translate at all. There's one, for instance, that revolves around confusing a train pass with a watermelon (yes) that I had to completely re-write because the direct translation was utterly nonsensical. Most of the major divergences are going to be for that reason. Others are minor things like not using names in lines (Japanese writers like to have characters refer to each other by name all the time, but it sounds hella awkward in English), or shuffling the order of information in a set of lines around a bit so it feels better in English.
