Should marital status and its international characteristics be included in a CV/cover letter?
For US applications, you absolutely should not include such information, as it can make for awkward situations during the hiring process. 

For applications in other countries, you may mention such issues in the CV where appropriate. However, you should not mention it in a cover letter, where it will seem contrived, artificial, or "stretching." People reviewing your application will not read anything into the characteristics of your marriage.