I don't know of any certificate that would really help in being prepared for Game Sound Design. What does matter is a complete knowledge on the topic of audio in general, and a passion for non linear sound design.
You need to be educated and experienced in microphone techniques and recording, in hardware and software routing and processing, in acoustics and computer science as well.
I would be skeptical of any educational program that was based around sound design as a main topic, before the world of sound and production were addressed correctly first, unless it was a graduate level program. At the beginning, you should find something that teaches every aspect of sound production, and focus your practice and skills towards Gae Game Sound along the way.
A good deal of indy level production of game sound will go along way. There is nothing to replace actually doing and practicing the craft. Get on a mod team, and put your heart and soul into the process. Make your sound design unique and original, and practice implementation as often as possible.
Good audio schools are very expensive, and do not guarantee you a job in the industry. However, the amount of information that you need to be a solid audio producer often goes beyond what you could possibly teach yourself.
Have you taken a shot at any production yet?