Is there a rule for when to use an article and when not to?
The lessons teach that "el papa" means "a potato" or just "potato," so when do you use the article and when don't you?
Also, "I speak English" translates to "Hablo inglés." Why doesn't it translate to "Hablo el inglés?"
You may have already seen it, but the reference article here. explains when and when not to use articles in some specific cases. Hablar is an exception. I don't know why, but it is. Note that it is hablar that causes the exception and not the word English.
The only rules I memorized were the ones dealing with professions myself. I know I must sound like a fool some of the time, but a lot of the time English and Spanish coincide.