Hi, if the dictionary you are looking for is not listed in the first post of this thread, then around there is no Kobo version already converted.
You might be able to find a StarDict Russian-French dictionary, and then you can use Penelope to convert it for Kobo, or ask someone to convert it for you.
EDIT: you might also want to look in the subforum on Kobo in French:
https://www.mobileread.com/forums/forumdisplay.php?f=261