We've noticed that the dogs we've had since puppyhood pick up a lot more from our general conversations that the ones we've had for less time. We talk to our dogs all the time so the longer they're here and the more they're focused on us, the more language they've picked up. Not just commands or the word 'hungry' or 'out'...but whole concepts like "let's take the dogs out back for a romp" or "seems like a good day for chews" or even "gotta fit in a birthday party".
Ember has the best language skills since we got him the youngest, and Macie (who has always been a bit more aloof because of her sad early history) is the least cognizant of what we're saying.