Taiwanese also use Han Chinese as their writing language though some of them might try to claim “闽南语” (Mian Nan Yu) as their national language. Japanese is completely different. I can guarantee you the four characters we saw are 100% Chinese though I can only identify two of them, but I guess the meaning is "do not stay near when operating."
I'd agree with Zaky that the gun might belong to the 071. If you enlarge his photo, you'd see a turret in the middle of the ship. It looks extremely like the photo I posted though it is covered by something.
5 minutes later: I zoom the photo and finally I can identify all the four characters "危险勿近" which means "dangerous, stay away".