Thanks Battara !
Here is some pictures after restoration, and I must say that I'm quite happy with the result (I will detail what I did later).
While doing some researches, I found this page :
http://www.vikingsword.com/lew/w1147/w1147.html, suggesting that this type of knives originates from Agadez, in Niger, and started being made during the last quarter of the 20th century. Which makes sense to me, as it seems like Agadez was a silverworking center during the 20th century, and because the Smithsonian keep some similar knives in its collections, identified as Nigerian or Malian.
Another thing I noticed during my researches, and which surprised me, is the relatively high prices that this type of knives sell for, while being relatively recent and not of a traditionnal type (or so I think), any idea why ?
Thanks in advance for your answers !