There is no formal certification for that, as in no test you can prepare for and take.
The process probably varies from region to region as well. Even within a given geographical area -- the Americas, for example -- the rules are different from country to country.
In the US, an instructor is usually vetted by Sun or a business partner. The candidate is required to observe the course they wish to teach, and then teach it once under the guidance of an approved instructor. The success of that event is judged by student reviews and the oversight of the reviewing instructor. At that point, the candidate is allowed to teach on a solo basis. Student reviews are the sole judge of performance from that point forward.
"Certified" Sun Instructor
Make visible what, without you, might perhaps never have been seen. - Robert Bresson