The pen in question looks a lot like this late Wahl Oxford pictured below:

I know it is difficult, but try to look at the blue pen on the right. Hey, Stop looking at the pens on the left...look at the pen on the right...
There are some peculiar things about the pen being inquired about:
The nib is not correct for the era of the pen regardless of the european karat marking, it was probably used as a replacement for the original somewhere along the life-line of the pen. The "WAHL" nib is from the 20's, and the pocket clip is very generic and also looks like a replacement. There were many pocket clips that attached with 4 tabs (the one in my picture does likewise), so non-original replacements would have been possible.
The Lever IS correct for the Oxford
The Plastic is the same in appearance.
It is possible that if the pen in question was intended for sale in France. If so, in the late 30's the "Oxford" imprint (English sounding, right) might purposely have been left off. (my guess)
If all this is correct the pen would have been made in the period from circe 1937-39. I would hazard a guess that as an Oxford equivalent would have current value of about $45-65. With the funny clip maybe 25% less.
Syd the Forensic Wahlnut
PS. The pen and pencil set on the left is the Equi-poised Ladies'Purse Pen in India Pearl...couldn't resist including it for show.