If I do not know the rules of a country, that does not count for that much in a court of law. I will still be punished for breaking the law. Likewise, if I do not know that bad speech results in bad karma will I be punished (in the sense of bad karma in the future )? Or maybe if I don't know what bad speech is will I be punished? To put the most extreme example, if I murder millions of people but I have a brain disorder and don't realize that is wrong, then will I be punished in the future by karma?
If you are ignorant of the cycle of day and night, or the phases of the moon, or even of gravity, your ignorance does not prevent them from happening. Universal laws are just that -- universal -- and they don't change for those who don't know of, understand, or follow them.
There is an element of intention behind all karma/action, and this intention factors into the quality of the actions. A wrong action done with pure intention is certainly less bad than a wrong action done with evil intention, but it's still a wrong action. The "brain disorder" example is interesting, but again, ignorance of universal laws does not halt or change the manifestation of the laws. One can never escape the effects of one's actions, regardless of the circumstances.
Even Angulimala could not escape the accumulation of karma from his time of killing:
Being an arahant, Angulimala remained firm and invulnerable in mind and heart. But his body, the symbol and fruit of previous kamma was still exposed to the effects of his former evil deeds. As an arahant, he needed no words of consolation, but a reminder of the kammic concatenation of cause and effect, which still has to be endured until the end.
Being ignorant of the repercussions is the very reason what we accumulate Karma which will give future experiences which the receiver perceive as unfavourable or painful, hence this this sense it can be considered a sin.
I've heard there's a tribe in Africa that speaks using a heavy and chronic form of sarcasm -- at first the academic from some Western university thought they were just messing with him, until he realized it was a cultural thing to prevent people from gaining too much pride.
https://en.wikipedia.org/wiki/Somali_Bantu#Profile A brief mention....
Let's assume there is a society like this for the sake of argument. Something like Wrong Speech would likely not exist, in the context of being a wrong action that leads to suffering, unless a person's actions were a lie that were to lead to someone dying or there were some other result of speech that could really separate people in a harmful way. As I understand right speech, it's abstention from right action; wrong action could be probably understood in a similar light. (In a society without property, theft would not really exist, for instance.)
If this kind of action is really universally prohibited against all humans, perhaps birth into life-long ignorance could just be seen as being as a unfortunate rebirth as the result of past karma. But I understand wrong view as meaning those that lead to harmful behaviors and beliefs, first and foremost...