Do you think your dog understands you when you speak to him? Or does he just associate the sound you’re making with a certain action? For example, does he understand what the word ‘sit’ means or does he just associate that sound with the action that you are expecting of him?

If your dog actually understood the words that you were using, you wouldn’t need to repetitively train him to perform a trick - he would just understand what you are expecting and do it. Dogs don’t speak English, or German or French for that matter. Dogs have their own language, which is based more on actions than sounds.