Please note that certificate programs can be very valuable. But I want to make sure that editorial professionals don't think they're the same as certification. Someone on one of the profession-related email discussion lists that I subscribe to conflated the two concepts today.
The page "Professional Certification vs. Certificate Program" of the website of the American Speech-Language-Hearing Association has a good discussion of the differences between the two concepts. Scroll down to the heading "Difference Between Professional Certification and Certificate Program." The chart in that section is especially helpful.
The United States does not have any organizations that provide certification of general editing proficiency. Note, however, that the Board of Editors in the Life Sciences provides certification of editing proficiency in the life sciences, and the Society for Technical Communication, whose membership includes writers and editors, provides certification of technical communicators [updated August 11, 2016].
The Editors' Association of Canada is one of several professional associations outside the United States that does provide general certification. Updated: Editors who live outside Canada can take the organization's certification examinations. The "Qualifying for the Tests" page of the organization's website says:
If you work in English—no matter what country you live in—you're welcome to take the Editors Canada certification tests. The benefits of Editors Canada certification are recognized worldwide. To take the tests, you must travel to one of the Canadian cities where they're offered. Two tests are available every November.
For more information, write to firstname.lastname@example.org.