The date the offer was posted online is displayed at the top of the description. You will also find the reference of the offer, its location, and the type of contract proposed.
All the offers are described in the same way. They are written by the recruiters of each company. The offers relating to opportunities in France, or in a French-speaking country, are written in French. Offers relating to opportunities in other countries are written in English.
The offers are updated directly by the recruiters of the relevant company.