You are right, that there can be differences. I am aware, that problems may arise everywhere. But if you compare the work required to translate a bishoujo game from Japanese to English with the work required to make a big game (like Starcraft 2, Sims 3, Mass Effect 2 etc.) from scratch, then obviously only a tiny part of the work to make such games is required to translate a bishoujo game. Nevertheless it takes about the same time (or sometimes even more time) to translate a bishoujo game to English (the time is measured from the original announcement to the release date). This can only be explained by the small number of people working on the translation of the bishoujo game and the huge number of people working on each of the other types of games.
The amount of information about the original game engine is obviously a matter of trust and payment. The game company which made the original game should be interested in giving information to be used to make the English version, because the original game company will be paid for their rights when the English version is made and sold. But it is obviously a matter about the deal between the two game companies. So if the original game company isn’t paid very much for their rights then they won’t help very much. But isn’t it better to pay them a little more then to use years of extra work to avoid it?