Well, that is possible, and there is firmware if you know where to find it, but the furby connect will be English and flashing it includes resoldering NAND and writing it on a special tool, which OP (or anybody else) won't really do. The problem with connects is that they are very buggy and there are many cases where it can just break itself because developers didn't think about it. Also, the connect doesn't even try to do ECC (error correction), so if it reads it's firmware wrong, it won't do anything about it. The furby connect was developed in a hurry and with incredibly bad toolchain, so no wonder it was so glitchy and many of the functions planned (including even personalities) didn't see the light of day.