I suspect you might not be surprised to hear that this is a loose adaptation of Shakespeare's play. It tries to go a bit closer to what little we know about the historical Macbeth, and also to give Lady Macbeth (Gruoch) a bit more of a role, but he broad strokes are still much as the play was, and it even includes some of the play's more famous lines. That last bit was a little odd to translate too. The author's foreword says that they used Victor Hugo's son's translation of the play as a source, and changed them round, but I found for the most part they were straight quotes. However it posed a bit of a problem in translation, I don't know how 'modern' that French translation would be compared to a contemporary French translation of the play, I don't know of a 'modernised' 1860s English version of the play and I certainly wouldn't want to try it myself, so I used mainly the original, but left the foreword in anyway.