Description:
------------
The description of log_errors is:
 log_errors boolean

    Tells whether script error messages should be logged to the server's error log or error_log. This option is thus server-specific.

        Note:

        You're strongly advised to use error logging in place of error displaying on production web sites. 


The French translation reads:
 Indique où les messages d'erreur générés doivent être écrits : dans l'historique du serveur ou dans error_log. Cette fonction est spécifique aux serveurs.

    Note:

    Il est recommandé d'utiliser l'historique d'erreur, plutôt que d'afficher les erreurs sur les sites de production.


The first sentence is incorrect. In English, it means:
 Indicates where generated error messages should be written: in the server's history or in error_log.


error_log is the directive allowing to choose how to log. log_errors is just a boolean determining whether PHP should log errors or not.

An appropriate translation would be:
 Indique si les messages d'erreur générés par les scripts devraient être journalisés dans le journal d'erreurs du serveur ou dans error_log.


Note that the French translation team should not take all the blame for this. The English version is fairly unclear. The following sentence ("This option is thus server-specific.") belongs to error_log's description, not here. I suggest replacing the whole English paragraph with just:
Tells whether script error messages should be logged.

The only problem with that is it doesn't refer to error_log, which the reader will naturally want to learn about next.