As you know, Nigel and I translate stuff from Chinese.
So translation of Gate is dependent on the Chinese translation.
Well, some guy translated Volume 4 Novel version in Chinese (depicted in the picture above).
It corresponds to Volume 7 and 8 Light Novel version of Gate that had been translated so far.
(book covers shown below.)
Which means... No volume 6 anytime soon.
If people want it bad enough, Nigel can do the (Novel version) volume 4. Do let him know in the comments.