The creature would start of with it's own preferences the same; A Badger would still be temperamental, a dog would still likely be loyal (assuming it was treated well), and a tiger would still desire to hunt to survive.
Then, over time with additional experiences, temperament would change. Now, as an Animal Companion, it is already in relationship with other intelligent beings that it can interact with. Such an animal would obviously retain all previous memories, and would now start making moral judgments and personal preferences about past and present experiences. A Badger may learn peaceful responses to situations, a dog be decide to serve itself first, a tiger may become very selective in the preference of how it acquires it's meal.
As for language, while I agree an
Awaken spell grants the ability to speak, but putting on a Headband of Intellect does not. I'd imagine a Druid's Wild Empathy ability would allow for efficient enough communication of preferences and emotional states, but not a discussion on morality or strategy. The animal would need to develop a form of communication, teaching it to write in the dirt on the ground strikes me as an effective method regardless of the creature, but expect a bear, peacock or elephant to learn to write as quickly as it takes a human to do so, which either means weeks/months based on real live, or the investment of 2 skillpoints for literacy if you want to go the D&D mechanics route.
in my
Rust Monster Mount Guide I hypothesized what might occur if a Rust Monster, which granted is an aberration, not and animal, but having in Intelligence of 2, acquired a Headband of Intellect. My conclusion was mutiverse-alteringly destructive, based upon what my guess is that an Intelligent Rust monster would value. The creature's priorities will strongly dictate the creature's actions, and those priorities are likely to remain the same regardless of the Intelligence score unless some strong intervention.
