Well it appears that you got your answer Andy. I was gonna guess it was French because of some other ones I had seen long ago.
They were similar but their blades were trefoil and quatrefoil shaped instead of square.
Stabbing bayonets and they were deadly in a very nasty way as your square one would also be.
When a stab wound is made by such an instrument the wound closes up when the instrument is withdrawn and so doesn't bleed freely to let out any poisonous bacteria that may be on the blade.
Such wounds are much more likely to become infected and fester causing lots of trauma in the wound.:barf: