See if this previous answer from Old Turkey will solve the problem: Why isn't my Furby Boom speaking?
A Furby is an electronic child's toy that looks like a small furry animal. The toy speaks words when powered on. Over time, a Furby speaks several English words, but when first turned on, speaks mostly in "Furbish," a word the makers of Furby use to describe the gibberish sounds the toy makes. Children are sometimes led to believe they can teach the Furby English words, but the Furby cannot actually learn new words from humans. The Furby is programmed to add more English words to its vocabulary the more it is turned on, making it seem like it's learning English.
Open the Furby's package and insert the AA batteries into the bottom of the toy. Turn the toy on. The Furby will say its name in Furbish.
Leave the Furby on for several hours each day. The Furby goes through three stages, advancing the more times it's turned on. In the first stage, the Furby knows little English, and in the second stage, the Furby learns more English. By the last stage, the Furby speaks more English than Furbish.
Feed the Furby and interact by placing your finger in its mouth. The Furby will indicate it's tired by opening its mouth. Put the Furby to sleep by placing it in a dark room. This type of interaction will introduce more English words. Over time, you should notice the Furby using more English words.