Yes, you might be right. I am not an expert in German grammar, but as a native speaker it sounded wrong to me.
Some additional thoughts:
In this case "das" would be a demonstrative pronoun I think, which refers to the object "Deutsch". So if you use "das" it should be accented.
I guess in this case one could say that the German language is not good.
If you use "es", this word can be interpreted as a personal pronoun i think. According to this one could substitute my German, which is a bit more precise.