For comparison, the original game is currently at 11898 sales. With the difference like that I doubt the dev would even bother thinking about translating the second game.
Yeah, after two years and with what looks like a team of around two dozen people of varying contributions, the Japanese version has sold a ton of copies, that's true. However in the english version in the credits, one person is listed for the English translation. Looks like they paid one dude a couple hundred dollars at most to translate all of the text, so low overhead for the translation.
If you look at other english titles on the site, they also seem to be around 500-1000 sales per year, and Black Souls seems to be keeping pace with that estimate, so at 15 dollars a purchase they're looking at 7500-15000 dollars of revenue per year. The entire game is already made, it just needs a single person to translate it. It's free money left on the table.
There is also the possibility that the translation was started a while ago and no matter how disappoint the sales, they'll just release it anyways because again, it's leaving money.
