Watchlist emails are in english for a wiki in french

Set the wiki in french instead of english as follows:

• in administration -> localisation:
  • leave multilanguage option to "No"
  • change the available languages to "French" (Simple french "fr", not "fr_FR" or others)
  • change the default language to the same value, French (Simple french "fr", not "fr_FR" or others)

For a user, enable watchlist mails (hourly) and make modifications in watched pages. The mail will arrive with texts in english instead of french.