I recently bought the French version of volume 38, because I wanted to know how they spelled the names of Ethan's and Jihan's masters. (for those who want to know, they transcribe them as Sero Rahmane and Silkwat Junazard.) And I was quite surprised about how nice this version is.
The first print edition(!) of the French version includes all extras, including the full outer cover, the 1st print bonus illustration, the inner cover and the omake. The arrangement on the outer cover is a bit different, but no illustration was left out.
The print and paper quality is very nice. It's actually even better that the original Japanese version. The paper they use is thicker, a bit whiter and smoother, the print is very clear, and the pages are a bit wider which means this version has a few millimeters more of Mr. Matsuena's art at the sides of each page.
I cannot say anything about the translation, because I only know a few words in French. All I can say is, that they translated all sound effects and that they only use the French names for techniques and did not include the the original pronounciation.
The only thing I find a bit strange is the volume numbering. They start counting from 1 again after the DoD tournament and call it "season 2" for unknown reasons. That means volume 38 is saeson 2 volume 9 according to their system. However, the original volume number is printed in some tiny font next to the "new" volume number.
Something else that might matter to some is that they replaced some cover illustrations on some of the early volumes with art from more recent chapters. For example, volume 2 features Kenichi and Miu from and illustration that was used during the DoD arc.
If I knew any French I would probably buy all volumes.
