US, French, British, and Chinese so far by my count. I might have missed some of the other leaks though.

Yes, sorry, I meant to edit this in but forgot :)

Is an open source game engine likely to cause those War Thunder forum participants with military clearances to become more angry in debates (because they can now see how the inaccuracies in specifications would impact the performance in game) or less angry?

Either way, I doubt the impact is zero. So as something that has military effect, it might be covered under ITAR after all!

/s