Yes ! Repair process OK ! French characters OK ! 
As I said, my Plex server is working well. Probably errors like
row 6533 missing from index index_media_parts_on_file
row 4449 missing from index index_tags_on_tag_type
are not a real issue. But apparently, Plex checks these errors and doesn’t back up the database.
I will see in few days if backup files will re-appear…
@OttoKerner Thanks a lot for your help !
PS : The database clean-up doesn’t fix my other issue : Adding music videos: french artists are not recognized!
