I was wondering whether bonus critical damage on weapons such as Steelfang also affects your other weapon.
It's difficult for me to test this since my Berserker is almost execute capped and it's hard to tell the numbers apart for sure.
If you look in the bottom tab on the left side of the screen, you'll find the Arcane Statistics. The top of this tab includes detailed information about your offensive capabilities. The first set of stats include a critical damage bonus that applies to all the weapons that you are holding at the time. Underneath, you will find individual stats about your right-hand and left-hand weapons.
I checked out my Berserker character, which has one weapon with a +20% critical damage bonus in my right-hand. The damage done on a crit includes the extra 20% bonus with the right-hand weapon, but not the left.