From someone who played it 4 times
I have played both the original game and the knife of dunwall/brigmore witches 4 times each for both endings and the ghost/cleanest hands and the flesh and steel achievements. There are lethal and non-leathal ways to do everything. The amount of violence is dependent on your actions though it enables mass murder and encourages stealth and low violence. There are quite a few sh*t and f*ck words in there when you or a rat are seen. The more kills, more rats, more cursing. You can use almost every lethal weapon in your arsenal to perform decappitations and dismembering enemies. Many city watch people grumble curses under their breaths. Most non lethal methods for targets ruin the persons life. One man is the leader of a cult and then a plague victim you can later encounter. One woman you can kidnap and ship away with a stalker of hers. A couple non lethal missions are worse than death. Throughout the whole game, you do horrible things to horrible people. Overall, it is only as violent or vulgar as you make it.
This title contains:
Ease of Play
Violence & scariness