hi guillaume
- install the same version of scribus on a different computer that you can put next to your current computer
- on the new computer go to the file > preferences
- find out where you have a latin language and pick it in both by counting the number of entries (if you have "no language" on top, pick that one... it's the easiest one : - )
- press on the "ok" button
- re-open the preferences to pick english.
if this does not work for you, you can delete the preferences on the disk and get scribus to start from a clean state... how you do it, depends on your OS.
on linux, you'll have to remove the ~/.config/scribus directory