Thanks for sharing your sample.
We have checked the sample and found that required culture script file is not referred which is the cause for the issue. Kindly refer the French culture file in layout page as shown below and visit the below links to know more about Scheduler localization.
<Code>
<link rel='nofollow' href="http://cdn.syncfusion.com/14.4.0.15/js/web/flat-azure/ej.web.all.min.css" rel="stylesheet" />
<link rel='nofollow' href="http://cdn.syncfusion.com/14.4.0.15/js/web/responsive-css/ej.responsive.css" rel="stylesheet" />
<script type="text/javascript" src="http://cdn.syncfusion.com/js/assets/external/jquery-3.0.0.min.js"></script>
<script src="http://cdn.syncfusion.com/js/assets/external/jsrender.min.js"></script>
<script src="~/Scripts/ej/web/ej.web.all.min.js"></script>
<script src="~/Scripts/ej/i18n/ej.culture.fr-FR.min.js"></script>
</Code>
Regards,
Karthigeyan