Although bold markdown has finally been fixed for Japanese, there are still occasional problems. I first noticed these problems in chat; it seems like there are related problems on the main site, but the behavior is slightly different in chat, so I'll try to illustrate both behaviors here.
I've created a test chat room with two problematic messages:
1. 行こうか**どうしようか** ＝ 行こうか**？？か** 2. 「許さない、（許さないのは）**絶対に**だ！」 → 「 許さない、**絶対に**だ！」
In this chat room, the messages render like this:
To compare with the main site, I entered the same messages into an answer on the formatting sandbox. I found that the first message has the same problem, but the second message renders correctly:
It's really nice being able to use bold markdown with Japanese! And it usually works fine now, so this should probably be considered a minor bug. But it would be nicer still if it worked more reliably.