Barbarian Mercenary shows 2 swords but cant dual wields

Title

I attempted to equip 2 swords on each hand like my normal barbarian character. also the in-game random barbarians encountered on 1st mission of Act V are wielding two-2handed swords in each hand. so I assume its a bug?

No it’s not.
barbarians in the wilderness are different critter than barbarian merc.
Barb Merc wields one 2-handed sword graphically and he can equip swords only. Be it one 1-handed sword or one 2-handed sword, ant that’s it. it’s the same way it has been in D2LoD.

Luckily to know they are unique in a way that barbarian merc can also equip barbarian class helms that (at least in theory should boost his skills, However + barbarian skills does not provide bonus to his bash nor stun, neither bonus to + barbarian combat skills does anything for the merc. in theory +stun and +bash should boost the skills, however due to a bug certain skills such as combat skills like bash or stun are not sepose to roll on any kind of helmets, only on weapons ( and no weapons have them in their rolltable), so all in all getting a barbarian helm with +stun and +bash is a consequence of game buging out.

good to know, then which merc do you prefer I use then ?

Typically folks go with act2 merc, due to them natively turning on a palladin like aura that benefits the player ( it requires exiting beyond city gates and letting act2 merc attacking some mobs for some time ( the aura trigger is chance on hit based, but once it’s on it stays until he or both of you die(s))…
All in all there’s a new patch coming that is going to make quite a stir in decision making around choosing a merc…

I also belive it’s tied to one of my posts regarding suggested changes to act 3 merc. The idea of using “Lower Resist when struck” Proc on one of their runewords, actually came from my proposed build using act 3 merc with built-in as conviction aura native skill coupled with “medusa’s gaze” unique shield which has a “Lower Resist when struck” proc… it was quite hilarious watching a3 merc 1 shotting down ex-immune mobs he couldn’t handle prevously, and beeing dependant on both the conviction aura and lower res proc at the same time. I have no idea if Blizz is going to copy everything as i described 1:1 or are the changes going to get some balance QA, but i have a suspicious feeling my mod going to get implemented into live build in one form or another…