Hi Bruno,
Yes, if you're talking about forms you created in Form Builder, apps/fr/login.xhtml should be used. You can extract that file and put it in the war as WEB-INF/resources/apps/fr/login.xhtml, then just try to change it to see if works.
If this has no effect, maybe check in your web.xml that your <form-login-page> indeed points to /fr/login.
Alex
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