The dual cart DQ9 is a bullshit rumor/fake. Not to mention even if it wasn't ALREADY dumped as a single cart (Japanese version), it wouldn't work period. The DS doesn't, and can't store a save file. Also, you can't just switch it out like a ps1 multi-disc rpg. The only plausible way they could of done a multi cart game, is to make an extensive, and massive password, like one of the two ways to carry over your file from Golden Sun 1.
But the sheer number of people actually BELIEVING it would be 2 carts, despite even the Japanese release being one, shows how ignorant and naive most users are about the DS, and news in general. Inb4 "FLAEM WAR", and "YOUS TROLLIN'", maybe you should look up ignorant, it's not an insult in most cases.