Hi! Are you saying "implacable" isn't used in this sense?
The second definition in the OED is "relentless; unstoppable."
I lifted this translation from an Arthur Goldhammer translation of Camus, for what it's worth.
Oh, sorry, I misunderstood. As you had reported in the English>French dictionary, I thought you wanted me to add "implacable" in French as a translation of "inexpiable".
You suggest "inexpiable" = "implacable" should be added in what we call the frbase, that is, to have it appear in the French>English dictionary, right?