In the security menu, the choice for this option is ambiguous.
And the translation into French (and perhaps other languages) doesn't help in making the right choice.

I suggest:
Changing the text of the option
Disable question script for XSS restricted user
to:
Disable the use of XSS scripting in questions for users with restricted rights:

Which would read in French:

Désactiver l'utilisation de script XSS dans les questions pour les utilisateurs avec des droits restrictins:

Then the help text:
If you disable this option: user with XSS restriction still can add script. This allows user to add cross-site scripting javascript system.

Then add the word "WARNING" in bold at the beginning of the sentence, as in the "Force HTTPS" section.

Which would read:
WARNING: If you disable this option: user with XSS restriction still can add script. This allows the user to add cross-site scripting to the JavaScript system.

This will avoid any misunderstandings.