I was really curious so I wanted to know: How much sales of anime in Japan is considered profitable? By sales I mean the DVD or something like that. I heard that anime season or continuation is based on the sales in Japan so, any guess?
That depends and the answer will vary per anime because the cost of making one season of anime varies. However, from here,
According to Masamune Sakaki, a CG creator in the anime industry, an average 13-episode anime season costs around 250 million yen (or $2 million).
If we take that as an example and say that each Blu-ray would cost at around 5000 yen, which is more or less the case if you look at some sites selling them, the anime would have to sell at around 50000 Blu-rays for break-even, and even more for profit and a budget for another season. This is only if they're trying to recover costs based on Blu-ray sales alone, but anime tend to have other merchandise you can buy aside from Blu-ray.