Hello, Gael!
Unfortunately, I can’t reach your website due to WordPress error.
Try to remember what you did before that happens.
If you found think some of the plugins caused the error, I suggest you go to your server where the site is hosted (You will need an FTP host, user & pass details from your server.) and rename the plugins folder, located in wp-content / plugins/, by renaming plugins folder on your server, you will deactivate all plugins. Then your website should work.
After that, let us know, so we can check what’s going on directly on your website.
Thank you.