I know you're doing another pass on the translation for 6, which is great. There's a few places where it's still clunky in 5c, and people occasionally talk in very stiff and unnatural ways. I'm trying to make a note of them for you.
Some that leap to mind:
The two people who talk about "planetary biology" (or "planetary bioscience", I forget) leap to mind. It's a very clunky phrase that needs to be changed up, rather than repeated, in order not sound unnatural.
Sephiroth in Cloud's Niblheim flashback also springs out ("What have I to be sorrowful about...?").
I seem to remember that Cloud and Tifa's trip through Cloud's mind in Mideel also has moments of being clunky, too, although unfortunately I can't remember any specifics.
I'll try and make a note as I continue my playthrough. (Usually it's the feeling that the character doesn't sound like themselves.)
Basically, as I'm sure you're aware, the edges still need to be smoothed off in a few places. I assume that's what you'll be attempting in 6.