My DM does a really good job of role-playing familiars. My owl familiar has gone from the intelligence of a child ("Yes, tall-magic- one, many wingless ones come toward you") to an average intelligence animal at 10th level ("There are four of them, tall-magic-one. One wears robes like you do.")
But as for understanding languages, I'd say the animal understands more as he gains intelligence, but certainly no languages that the Wizard/Sorcerer doesn't understand.