From the point of view of the person who wants to become a trainer, the answer may be pleasing. In reality, since anyone can call him or herself a trainer, thus hanging out the business shingle, there are actually are no official lists of qualifications, particularly if you want to run your own training seminar business.
Since barriers to entrance into the career are so low, or non-existent, you will find successful trainers coming in from all kinds of other careers, from social work, to computer technology, through to psychology, and public school teaching.
That's not to say that having qualifications and/or credentials aren't a help. They are, but many trainers succeed in training businesses without having completed formal education in the field. And, having qualifications (like relevant experience, courses taken, etc) or not having them is less important than having the SKILLS needed to be an effective trainer, seminar leader, or training business owner.
In training, as in other unregulated fields, success may actually be dependent on the ability to market and plan your business, rather than on any qualifications, or, sadly, a person's ability and skills.