The translation manual is received from Ak-Haranu during the Ghosts Ahoy quest. He will give it to you in exchange for an oak longbow signed by Robin, who is staying in the nearby The Green Ghost. Once obtained, give it to the Old Crone to continue the quest.
How to Obtain
First, talk to Ak-Haranu. He will tell you that he has the manual, but will only give it to you if you bring him an oak shieldbow signed by Robin, the master bowman. Talk to Robin. He will refuse to sign the shieldbow, but will challenge you to a game of Rune-Draw. Win the game four times, and Robin will sign the oak shieldbow to repay the debt. Take the signed oak longbow back to Ak-Haranu to receive the translation manual.