@hawhill, Ken Maltby, WS64
Thanks for your replies.
I need a little time to provide you online with the most up to date free hyphenation dictionnaries in my language (French). I do this a.s.a.p.
For the side-loaded font with my Kobo Glo, I use regularly
Linux Libertine otf. I am used to add a little weight to it and I had installed the -deprecated- Kobo Patcher v. 07 which allowed to replicate the advanced Type Genius features to side-loaded fonts. I still use v. 2.8.1.
Now, I think GeoffR patcher does the same trick (sharpness and weight). The problem for him is that he has to issue a new patch for every Kobo version, because his patch is not official. This should not happen for koreader.