The input of XTranslateCoordinates are ints however internally the values are clamped to shorts.
From looking at the source code this is intentional however its really not useful when getting offscreen coords.
Reported as a bug in blender.
The X protocol defines coordinates as signed 16 bit intergers.
Changing this would require a protocol bump, to X12. as discussed at:
but no one is seriously working on that.
Closing as "WONTFIX" ... this is documented for X12 if that ever happens.