Welcome, as Titus said the thai and burmese used double swords, It is called Daab song muu
http://dharesearch.bowditch.us/Images/Image435.jpg
They are also used in WMA many of the Italian manuals from the 1500s cover using two identical swords: Manciolino (1531), Marozzo (1536), Agrippa (1553), di Grassi (1570) One example would be as inas in a "brace of rapiers" or "case of rapiers". Another would be references to Case of Falchions.
http://storm.alert.sk/fencing/hutton/case.html
http://www.musketeer.org/manuals/diGrassi/contents.htm
They are used in chinese sword arts with Jian, Dao, hook swords, butterly swords and probably many others I know nothing of. ( Scott Rondell or Phillip Tom would be an excellent source for more on this ). Minamoto Musashi used and taught the use of dual japanese swords. Dual blades are used in Philippine Martial arts ( doble espada and espada y daga techniques),espada techniques can clearly be seen in the double stick (doble baston or doble olisi) techniques these styles teach. Check manuals on Escrima, Kali or Pananadata.
They are used in Pencak Silat. I have seen reference to them in Korean sword work. And I believe they were used with some indian and arabian or persian sword styles ( but I could be wrong on this one ). there is some evidence that double swords were used in Aceh but I have yet to find as much as I would like on that.
So while it was probably not a common battlefield technique . Sword and some form of shield probably dominated there. It was not uncommon. I hope this helps.