I can't do anything vs I can't do nothing

One close friend of mine moved to Georgia, USA two years ago. She used to be an excellent teacher of English in Vietnam. When I came here, we often contact in English via phone- like a kind of speaking practice. In our conversation, what confuses me is that she sometimes says "I can't do nothing" or "I can't go nowhere". What? Does she means that "I can do anything" or "I can't do anything"? Clearly, she implies that she can't do anything. So, does she make a mistakes in using English?

The answer is NOT REALLY. I have realized that what she says clearly shows what she implies. She is using non-standard English (not a standard English that she used to teach in her class)! And centainly, it is not wrong.

According to Eckert and Mc Connell-Ginner (2004) in Language and Gender, the second negative such as "nothing" or "nowhere" reinforces the first negative (p. 74). Similarly, in French, both "ne" and "pas" mean negation, but they both exist in negative sentence, such as "Je ne sais pas" (I don't know). How interesting!

However, this reinforcement depends on the language you use. In Vietnamese, if you use two negative features in a sentence, this sentence has affirmative meaning. For instance, "Tôi không thể không đi đâu" ("I can't go nowhere") does really mean "I must go somewhere".

And more deeper, do you think there is any reinforcement when you use -s (plural) after nouns while you already put "two", or "three" in front of the noun to show plural, such as "two tables"?