Translate the language file at <root>/administrator/language/en-GB/en-GB.plg_joombri_jblancefeeds.ini. If your default language is French, then translate it and copy it as <root>/administrator/language/fr-FR/fr-FR.plg_joombri_jblancefeeds.ini. Please note that the language code is different for different languages.
If you have done this step, all the future user activities / feeds will be translated and saved into the database.
If you have missed to translate the language file (explained in step 1), the activities will be saved by default in English. Hence you need to translate the content of the table xxx_jblance_feed. If there are so many entries, please remove the old entries from the table.
* xxx is your table prefix.