Conscious consumer covers the ethical part of 'consommacteurs' and I think is closer to the mark than 'discerning' or 'engaged' consumer.

Hope this helps

These links may also help.
https://www.theguardian.com/women-in-leadership/2015/apr/02/...

http://www.nielsen.com/us/en/insights/news/2012/the-global-s...

... seems to be another term used
https://www.fastcompany.com/3022143/creating-the-committed-c...
a quote from this page:
A conscious consumer says, “I recycle because it’s good for the earth.” and follows through on this belief when it involves something simple, like properly disposing of a water bottle. Or when others are watching.

A committed consumer says, “I want to protect the environment.” Not only does this person consistently follow through on this mantra, he or she thinks and acts much more holistically in pursuit of his or her beliefs. Instead of placing items in recycling bins, they are more likely concerned with not using unnecessary materials in the first place.

The distinction is important. Conscious consumers force companies to be more conscious. Committed consumers lead to more committed companies. Here’s the difference.

Another link:
http://ecoconception.oree.org/EN/committed-consumers.html

This is the term proposed in the futurelearn.com article (see web ref.) - but I'm not quite convinced this is an appropriate match for the definition in your text. The article may contain something else of use to you, though.

There are also a few hits on Google for the use of the French term in English (see the Google Books ref.), so maybe you can just stick with the French!

Finally, there are also some suggested translations on Termium: http://www.btb.termiumplus.gc.ca/tpv2alpha/alpha-eng.html?la...

A similar term is being used in English. Just google it.