I can't get quite get the joke across right, but Eirin is asking デキてる？ which like, literally means "are you able?" but also possibly "are you two getting intimate?" and there's some confusion but then hilarity ensues.
The only thing I can think is instead of eirin saying intimate, say "an item"? It would keep in line with the joke that youmu is good at using every day items.
Oh? Youmu, you're holding your chopsticks in your left hand?I can do it either way.You can write with your left hand too, huh.Yeah, I can.It's because I learned to swing my swords with both hands.You two sure are such good friends...Wh-!? w-w-w-w-w-what the heck are you saying, master!?... could it be you two are... a couple?Well, I am pretty good with that...Because I can swing my swords with both hands.Because my swords swing both ways.Every instance of this phrase is the same in the original, literally "dual-wield swords".
