In translational motion, for an isolated system, the net internal force acting on the system is zero according to Newton 3 law. But for rotational motion of an isolated system, does the internal torques cancel one another?
The internal forces don't cancel each other they are just equal and in opposite directions. This results in an internal momentum change of zero. The same is true for angular momentum. As one object in the isolated system begins to rotate another object must rotate with exactly opposite angular momentum so there is a net change of zero.