elwin:
Don't know if there are any texts on it, but certain Okinawan schools of Martial arts do use two weapons. My Goshin Jutsu training led me to Sai, which are basically two parrying/striking weapons, very similar in design and shape to the Main Gauche, also used for sword parrying. Other paired Okinawan weapons styles are Kama (short sickle type scythes), and Tonfa. There are Katas (forms) designed for each of these styles (they have their similarities) so you can get a feel for the flow of two-weapon fighting.
Also, there are a lot of antique and ancient paired jian (or gim), a chinese straight sword, similar to european short swords. They actually have some pairs that are both stored in the same sheath, suggesting that the user might manipulate both at the same time. In a culture that did not make wide use of the shield, you might as well fight with a weapon in each hand.
In europe, where the shield saw use as a defense, it seems that the shield + weapon combo previaled over two weapon. It's too hard to stop a spear, arrow, etc with jsut two blades, blades that may not have been designed for blocking in the first place. In many cases, small shields like bucklers, targes, or viking center-boss round shields, were employed actively, almost as a weapon. Some had spikes for a punching attack. Also, smaller shield can be used to pin or negate an attack before it starts.
my two pence.
Keith