For pages such as:
- Home
- Features
- Download
..and header and footer menus,
the changes take place in *.po files.
You will find those files in folders such as i18n/fr_FR/LC_MESSAGES/ .
Such files can be edited with softwares such as PoEdit.
To translate the tutorial, you will find .html files in folders such as i18n/fr_FR/contents/tuto/, where fr_FR is the language code for the French (fr) variant that is spoken in France (FR).