Being a foreigner from the outside I am well aware of double negatives.
Fact is that I am from Bavaria (southern part of Germany), and the bavarian dialect makes very creative use of the double negative:
Similar to some dialectal English, Bavarian employs both single and double negation, with the latter denoting special emphasis. For example, compare the Bavarian Des hob i no nia ned g'hört ("This have I yet never not heard") with the standard German "Das habe ich noch nie gehört".
Servus
