I knew a dog that had a decent vocabulary. He would visibly react to words like CAR, WALK, or PARK. He also understood PARTY and MEAT and would wag his tail for PART and lick his chops to MEAT. One time we were going to a BBQ so I explained to him we were taking the CAR to a MEAT PARTY and he got super excites, wagging his tail and going to the door all while frothing at the mouth. Anecdotal but it certainly looked like he could synthesize concepts and imagine what was going to happen in the near future.

I've done a few other experiments with my foreign speaking friends and it appeared to me that dogs understand the language their owners speak primarily.