Studies show dogs have the capacity to learn over 165 words, and they share a similar level of intelligence of a human toddler.
However, a dog doesn’t understand any word until we give it meaning. Language has no meaning to dogs – until that word is specifically taught to mean a certain behaviour. We could teach a dog to ‘sit’ with the word ‘sandwich’, however it's easier to teach using words that make sense to us (and that are easier to remember).
Sometimes when our dogs don't listen to us we will change the words we use, so instead of saying 'come' we will get frustrated and say 'come here, over here, come on', but think about how confusing that must be to the dog? If you were learning a different language and certain words changed randomly for no reason, would you understand?
A dog doesn’t understand any human word until we give it meaning.
When teaching a dog to learn a certain behaviour, choose your cue carefully, and be consistent. Use a word which won’t be confused with another, for example don't use the cue ‘down’ for ‘lie down’ when your dog already understands ‘down’ to mean - jump down off the sofa.
Why not write a list of cues on a piece of paper and put it somewhere you will see it frequently, like your fridge. That way, you, your family and friends will be reminded which words to use which your dog will understand.
Sources:
The Power of Positive Dog Training - Pat Miller
American Psychological Association. (2009, August 8). Canine researcher puts dogs’ intelligence on par with 2-year-old human [Press release]. https://www.apa.org/news/press/releases/2009/08/dogs-think