Hi, @gwadaelle. So nice you want to help finish a drama. Any drama.
Old channels are mostly inactive. So in order to save your subtitles by locking an episode translation in French, you should contact Viki directly and ask to be the French moderator on that project. This process is usually simple, but can take time to be resolved. You can contact Viki on https://support.viki.com/hc/en-us/requests/new
Unlike @jadecloud88 I think you SHOULD start translating it because the drama might be too old for any of their team members to still be active. We have done this before. If you start translating, it shows good will and capability to Viki. I understand why @jadecloud88 said what she said. We have many problems if people don't follow community rules, particularly in new projects. But I feel this is different. It's in the best interest of the project and the viewers that you start translating. Particularly because months can pass before you get moderator rights.
P.S. Considering how you are just starting to translate here on Viki, I would take a mentor, an experienced French moderator to check your translations in the beginning and guide you a bit with ins and outs of the Viki subbing. It greatly improves sub quality