Would interest upstream probably.

They use https://www.transifex.com/projects/p/discourse-org/ to perform the English to French translation.

But when I see the poor quality of the translation based on the headings you give ("Qui me parle ?" and "Quand est-ce que", seriously?), I wonder if locally, we shouldn't write our own welcome text instead.

(This task will need another volunteer than me. I'm not interested to fix French translation tasks ah this moment.)