[Two9A]

Arabic is on the Semitic branch of the hypothesised proto-Indo-European language, which has dual number: https://en.wikipedia.org/wiki/Dual_(grammatical_number)

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.

[eigenspace]

The Semitic language family is not part of the proto-indo-european language family. It's from the Afroasiatic family

https://en.wikipedia.org/wiki/Semitic_languages

https://en.wikipedia.org/wiki/Afroasiatic_languages

[kevin_thibedeau]

Persian is PIE and had influence over semitic languages in cultural contact. The connection could be there.

[z500]

Egyptian had it, and although it's Afroasiatic it's not Semitic, so it must have gone back further than that.

[another-dave]

Within Indo-European languages, Irish has the concept of the dual. It's used with things that come in pairs like "mo dhá láimh" - my two hands.

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>.

[mathieuh]

Semitic languages are Afroasiatic, not Indoeuropean.