The log contains an exception reoccurring quite often, so it could well be the culprit of the lag.
It was just a simple debug log in exit method of Vampires blood drinking behaviour,
which was accessing the destroyed unit when it was killed after sucking blood from it.
This made it failing in a loop causing a spam of exceptions, which slowed down the game.
However there is no reason to have this debug log at all and I removed it, which hopefully fixes this lag issue.

Unfortionately it is too late to get this fix into the newest hotfix update 1.4.f10,
so it will take another update before it will be (hopefully) resolved.

Please let us know if the issue is solved for you after 1.4.f11 is out.

Cheers

Josh Bishop What do you think?

Josh Bishop these guys don't have a gold need and thus Gild can not apply to them.
What do you think about this ticket?

Hah it was our failure that the game did not load when someone puts an invalid language index into the options.
But as said, it will be fixed next version.
I am glad it is fixed for you now.
Have fun! :)

I just implemented a fix, which will make the game fallback to English, when game options refer to a non existing language translation column.
Next Patch or Hotfix update will contain this fix.
We are sorry for the inconvenience we caused to all Japanese players using the "War for the Overworld日本語化プロジェクト" mod.

Thanks a lot for pointing us to this issue, NoobNooberNoobest.