Since I talk about Ranma a lot on this blog I'm going to point out the part that Ranma would find the most useful.
This basically means that Ranma can not legally be forced to marry anyone by Japanese law. Of course most of the Ranma cast don't care about the law in the first place or don't care about Japanese law. Of course Ranma is still honor bound to marry a Tendo and Ukyo, and it's Shampoo's people's laws not Japanese laws that bounds her to him. Remember what is honorable is not always legal and what is legal is not always honorable.