I read a book translated from English to Japanese, and I could tell it was not originally Japanese. The kinds of things described, how the characters talked, and some of the phrasing, you could kind of see through to the original language, if you know what I mean.
And often when I read books about Japan that were written in English, I notice phrases that would be very difficult to translate into Japanese!
I wonder if it is harder to tell with languages that are more similar. My Spanish isn’t good enough to detect those nuances yet.