Manual:$wgCookiePrefix/fr

Détails
Préfixe pour les cookie et les données du navigateur semblables (incluant la Mémoire local). Set it to use a custom one. Setting it to  or an empty string sets the default of using the database name. Code should ensure browser saved data is prefixed with this value (this is currently done automatically only when WebResponse->setcookie is used without a custom prefix).

The default value is determined in :