Comment area

i already saw a question like mine but i didn’t found the answer that i was looking for. Please someone tell me how can i change the language on the comment area. what i want to find is where is for example the file that contain the phrase – leave a reply – so that i can change it to my language (French) and i want to do it in all the comment area. I would welcome any kind of help that can lead me solve this question.
Thanks!!