Are buttons on different sides of clothing for men and women in all countries?

No, this is only tradition in certain countries. There is no consensus as to why this tradition originated, but some of my favorite theories are (and obviously these originated in an era with practically no equality):

* The buttons are opposite so that women can more easily do the buttons up on a man's shirt when dressing him.

* Mens buttons are so that when a sWord is drawn from the left hip by your right hand, the hilt of the sWord will not get snagged in the shirt. For women, they were not meant to fight, and so their clothing was opposite to "demonstrate" that they were peaceful.