Are double negatives proper English (e.g. "I don't know nothing")? [duplicate]

The second one is correct for most dialects of English. The first one is a double negative, or as we call it in linguistics, exhibits negative concord. Wikipedia has a pretty good article on double negatives:

http://en.wikipedia.org/wiki/Double_negative

Most prescriptive grammarians will tell you that a double negative is incorrect because it is "illogical." However, there are many languages that operate just fine using double negative obligatorily. For instance, almost all Romance languages have obligatory negative concord:

• Italian: Non so niente.
• French: Je ne sais pas.

Double negatives used to be grammatical in English, but there was a grammatical change sometime during Middle English. The Wikipedia article gives a sentence from a 1644 letter by Oliver Cromwell (emphasis is added by me).

A little after, he said one thing lay upon his spirit. I asked him what it was. He told me it was that God had not suffered him to be no more the executioner of His enemies.

The double negative is still used in many modern dialects, but it is typically very stigmatized.

The New Oxford American English reports that anything is used

• in negative, or questions to refer to a thing, no matter what.

  Has she found anything?
  Nobody was saying anything.

• without negative, for emphasis.

  Albert was ready for anything.

Nothing is used in sentences like

She said nothing.
There's nothing we can do.
They found nothing wrong.

Using nothing (which means not anything) in a sentence with a negative is using a double negation. I imagine the double negation can be used in some particular cases to give emphasis to the sentence.

The NOAD has also the following note (reported in the Oxford Living Dictionaries for double negative) about the usage of double negatives.

In practice this sort of double negative is widespread in dialect and other non-standard usage and rarely gives rise to confusion as to the intended meaning. Double negatives are standard in certain other languages such as Spanish and they have not always been unacceptable in English, either. The double negative was normal in Old English and Middle English and did not come to be frowned upon until some time after the 16th century, when attempts were made to relate the rules of language to the rules of formal logic. Modern (correct) uses of the double negative give an added subtlety to statements: saying I am not unconvinced by his argument suggests reservations in the speaker's mind that are not present in its ‘logical’ equivalent: I am convinced by his argument. According to standard English grammar, a double negative used to express a single negative, such as I don't know nothing (rather than I don't know anything), is incorrect. The rules dictate that the two negative elements cancel each other out to give an affirmative statement, so that I don't know nothing would be interpreted as I know something.