Hi Fabrice,
This does look worth posting across our social media channels! This would be the kind of thing we would want to write original copy for.
As for a concise criteria of what we post on via our sm accounts, it's still a work in progress.
I can tell you that we almost always distribute traffic to our blog posts via our sm channels.
We usually post positive coverage we may receive by major reputable publications (predominately English at the moment) as an exercise in public relations. For example, the New York Times did a feature on WikiProject Medicine back in October that proved to be very popular, and expanded our overall reach and translated into more followers to our page.
Appearances by important individuals as Lila and Sue Gardner have been featured, especially if there is a video interview (i.e. Lila's appearance at Code/Mobile).
If there's an important event pertaining with like-minded organizations ( i.e. EFF, Creative Commons, etc.) it is appropriate to show solidarity. For instance, it was prudent of us to bring attention to our followers that Nov. 8 was Aaron Swartz's birthday.
We tend to not want to RT a lot of things, but for the sake of timeliness, we we do.
I've only been doing this for a couple of months so I'm the same as you! I'm sure my fellow team members will give you more details than me!
Hope this helps!