I was kind of disappointed when my Ranger hit 4th and I got to pick a feat and there was no Dual Wielder in the list.
I'm assuming that this is not one of the licensed feats and therefore off limits. :(
So, here's a lore-friendly suggestion for a replacement:
Duality of Maraike
Your devotion to two weapon fighting has earned you a boon from the goddess Maraike.
While wielding two light weapons, the life aspect grants you +1 AC while the death aspect grants you an extra 1d4 Necrotic damage on each hit. (or maybe a straight 2 pts of Necrotic?)
Balance-wise, I think this is on par with the the Dual Wielder. That allowed you to wield non-light weapons so you could increase the damage done by using two d8 weapons instead of two d6 weapons. Adding d4 or +2 damage would compensate for the feat only working with light weapons. Making he damage Necrotic is more flavor than anything, and appropriate to Maraike. (Her Oblivion clerics get +d6 Necrotic at 6th level, so... seems fair.)
The +1 AC is a straight borrow from Dual Wielder (obviously) so there shouldn't be any balance issues with that.
Anyway, if you could add this (or Dual Wielder, or something similar) I would really appreciate it and I suspect other dual-wielding rangers would too.