Hi, Sandrine @781987!
Welcome to the TWB!
You have come to the right place. Well, let’s begin with the free ones, then we advance to the paid ones.
I recommend CW-ELAB course. It’s really good. The first tests demand a more agile thinking, but the last ones are “normal” in terms of speed.
We can’t forget YouTube videos, right? I recommend Freelanceverse; Freelance Translator Tips; and Localization Academy. Don’t forget Tess Whitty’s marketing tips. Sorry, I know more about Brazilian translators.
If you want more knowledge without paying for the certification, there is a course about project management on Coursera. It will help you see from a Language Service Provider (LSP) perspective.
You can also invest on books. It works more than courses for me. I highly recommend How to Succeed as a Freelance Translator by Corinne McKay.
Now, for the costly ones, I recommend you to have a Plus membership on ProZ, because you can access more than 500 videos about translation and interpreting, and can see the past events.
But if you want to take more affordable ones first, then these are for you:
How to be a Successful Freelance Translator (awesome tips, especially for invoicing).
Master Machine Translation Post Editing & Emerging Jobs.
If you want to translate games, I have more resources for you.
Remember to take courses in your translation specialization. For example, I translate IT materials, so I take courses in this topic.