Think how many languages are on planet earth, yet most movies have the aliens speaking a language of the country the movie is being played in. Except the newest Star Trek show, which decided to create a new language for a rival faction, and sub title everything they were saying. I turned it off because I couldn't understand anything being said and got tired of reading sub titles.
Animals are similar. They learn some commands but they don't know English. I tell people this all the time. Animals that can't be domesticated by humans should not be held captive. Dogs are the best because they "understand" what humans are saying, especially labs.
How is my brain wired? I do have an internal monologue. The voice is always talking about things and it's in English. Now imagine animals if they don't have a language, what are they thinking?