can't say for sure that b's understand everything, but I do believe it really helps them when you talk to them. I always tell my b what I'm going to do and what I expect.
So do I. Always have. maybe its just the reassuring sound of Mom's voice but 'I have to go out now, will be back very soon and its raining outside so you would hate it anyway !' seems to help.
Talking to my dogs and horses has always been my way, and they understand more than you think. Dogs especially will learn to pick out the significant words, although they also read your body language extremely well. I would argue horses read body language even better!
One thing I have practised since reading Charles Eisenmann's books is teaching my dog specifically to listen and pick out the pertinent information in my verbal ramblings, e.g. I might mention in passing that "I would kill for a red bone right now", which resulted in Perry bringing me his red bone without a "formal" request to do so....of course, if you reward the behaviour you will find your dog paying even more attention and finding the information encoded in your speech. It's a fun technique. Another example when a dog is underfoot in the kitchen "be somewhere that is not here!" or a variation on the theme. My dogs understood me very well.....and learned the meaning of many phrases that could be spoken casually and result in a response from my dog.