We don't tend to announce promotional sales beforehand since that would mean 0 income between the announcement and the actual sale, which makes no sense to us. We don't always plan our promotions several days ahead either. In fact, we submitted strings for translations with less than one hour left for today's launch.
Anyway. Yes, we are having a Black Friday campaign available: https://project-gc.com/Home/News?goto=101
No, we have not decided of when it will end. It will run for the weekend at least (UTC).