Rosetta Stone are one of the GF Learning Items in Final Fantasy 8. Listed below are the effects of the Rosetta Stone. Where you can find the Rosetta Stone and how to obtain the Rosetta Stone.
Rosetta Stone - Allows the Guardian Force to learn the Ability x4 ability - The Rosetta Stone can be won from the card player in the D-District Prison. It is also a reward from trying to enter Cheryl's Shop many times at Esthar. It can also be refined from a Shaman Stone
More guides can be seen at the Final Fantasy 8 Forums.The complete list of all GF learning items can be found at FF8 Guardian Force Learning Items Guide. If you have more info about Rosetta Stone please post them below.