Hi,
I'm also French speaking. So, we should not have any problem to understand each other.
To come back to your question, I used to work at IBM Belgium and provided support for TSM to customer based in Belgium, Luxembourg, France and Middle East. After 6 months in the team and one implementation, I successfully passed the certification. But, I was doing only TSM at that time.
Then, I moved to an IBM partner and was doing many other stuffs than just TSM. But, I had to renew my certification after 3 years and passed exam successfully again.
Therefore, according to me, it really depends how confortable you feel with the product. I think there is a test exam on IBM website. If you do not pass this one (which is normally easy) forget about certification.
To help you prepare exam, I would recommend the following redbook:
SG24-7127-00 (IBM Tivoli Storage Manager 5.3 Certification Study Guide)
Regards, Olivier.