You can find Jacobs prophecy for Naphtali at Genesis 49:21 (read).
When it says that "he is speaking words of elegance" it is talking about Jesus who fulfilled this prophecy by using appealing words as he taught others the truth in Capernaum (territory of the tribe of Naphtali).
When Jacob described the tribe of Naphtali as a "slender doe" or slender hind, it refers to the skill and swiftness that the tribe would have during warfare. One great army leader, Barak, was a Naphtalite. When Barak called to battle against the army of Sisera, the Naphtalites (along with the Zebulunites) responded with 10,000 men.