Just curious if you're working with a template override of the form.
Reason I'm asking is the function Joomla.submitbutton is typically added to the page by the template for the form.
Also, Joomla.getOptions is defined in core.js, which templates can avoid or block loading.
My guess is you're using a template that has decided for whatever reason to stop ...
So as Lodder answered guys, you can download all the language / translation php-files for joomshop via this link https://www.webdesigner-profi.de/joomla-webdesign/joomla-shop/downloads/languages.html?lang=en (registering (free) required for the download).
unzip the downloaded zip-file of your language, and look for the php-file under JoomShopping-lang-...
Based on Fari's link (Update 2) here is the solution:
<?php $oldLocale = setlocale(LC_TIME, 'fr_FR');
$date_string = utf8_encode(strftime('%d %B %Y', strtotime($jitem1->publish_up)));