I would say 46+ k€, before taxes, which are 33% corporate tax rate and ~30% on personal income. But I'm not sure how it applies to people with tech visa.
46k is really low in France for an experienced dev and that's outside of Paris. Junior dev engineer earn at least 45k when they begin in Paris, and it gets to 60k in about 5-10 years. Also corporate taxes are about 23% but you're right on personal income.
I've had my Engineer's Degrees from ISEP last year and I'm working at Alten since October 2016. My official title is development engineer (Ingénieur d'études).
Before that, I've done two six-months internship as a junior java dev.
Alten is a technology and engineering consulting company, which means, in the context of the French market, that when a company, need a particular profile (like java dev) to staff a position for a set amount of time (like for the expected duration of a project), they'll contract Alten for a developer, java, for x months.
Does it track market rates? I've worked for a company before that took fresh grads, and relied strongly on them never entering the market for themselves and realising what market rate was.