Change the language of older article and newer article (previous next links)

Hi !
I would like to change the language of the words older and newer article (need to translate to French).
Now, I know the best solution you recommend is to translate the .PO file but in this particular case, i just need to change just a few words so is it possible to replace only these words ?

I already did it for the comments by replacing the words in the comments.php file, so here i tried to find them in single-post.php, content-post-standard.php,… but i can’t find where they are.