>>4527710That's a question of localization, really. Some translators have converted lines like that, but a lot will do a literal translation the whole way through because they're uncomfortable with changing the author's own words. The latter isn't necessarily wrong because many readers have a "keep it the same, but with words I can read" attitude.
To use your example, it's likely that the author has already used "fuck my ass" by itself before throwing "ass pussy" out there. As a translator, would you want to shrug your shoulders and type "ass pussy", or do you change it to just "ass" and lose that "ass pussy" feeling? You can add "I love it in the ass", but then you're adding something the author didn't even write. It's alright if it works, but amateur translators and even readers might not be interested in "localizing" a work like that.