Personally I look at similar to wraithstrike. An animal companion is just an animal, it doesn't matter how "smart" you make them they're just an animal and their brains work differently. The only way for an animal to know a language is through the spell "Awaken" or something similar. So basically, you can have an INT 10 _____, but it will only be able to do things that it's commanded to or things that are natural to it like an INT 2 version.
Now if you do decide to Awaken and animal companion I use the Animal Archive as a guide and go with that the animal can no longer serve as an Animal Companion and you have to take the Leadership Feat and treat it as a Cohort.
To me, this keeps things simple and elegant.