More like: I ain't hurt you no more. 英语中的双重否定只是为了加强语气，这点与中文不同。

This is a very informal - lower class - expression used all the time in the UK and USA. It means, “I’m not saying anything”. Eg: Teacher: “You’re not leaving the lesson until you say why you did that”. Student: “I’m not saying nothing”.

Like others said, it's a colloquial way of talking. Very informal in English. Listen to the tone in which someone says something like that. If they're speaking very definitively, hear the "no" sound in their tone. They're not going to talk. This is rare, but if someone says, very carefully, carefully emphasizing certain words, then they might be saying, "I'm saying something, but you need to work carefully to get my meaning." I'm not saying nothing, my words are not nonsense, I'm saying something, but I can't say it directly.

Generally a bad sentence in English from a person teacher point of view. Sentence should read. " I'm not saying anything" simpler and way more precise.

In a simple and likely context, it means the person won't or doesn't mean to say anything or give any information away. It is a double negative therefore it is grammatically incorrect to say something like this. On the other hand, it's not rare to see this structure in spoken English. In a less likely context, a person would be trying to act smart by using this structure, and you can logically deduce that if the person is "not saying nothing", they actually are saying something after all.