Arabic has dual subject pronouns. I wonder if the concept developed independently or if there was any influence somehow?
It's interesting that we notice a similar pattern of losing the dual in many languages. And it would be very interesting to find the opposite pattern: a language where the dual newly develops out of nowhere. However, I do not know of such language.
So you'd expect to see languages from western Europe to south Asia that either have the dual concept, or have an attested ancestor that did.
Interestingly, to say one-handed you'd say "leath-lámh", where _leath_ means half, so half the <thing that's usually one of a pair>.