In 10.0 since 52f268d0 some parts such as the date/datetime widget are
adapted to the current locale and not just displayed in english.
But the dates in the slides module are always in english because they
don't wait for the locale to be loaded.
To wait for the locale, this commit also adds a reference localeDef on
the website.website module.
note: this fix is only for [10.0,11.0[, another fix must be done in 11.0
opw-804555
closes#22241
Nicolas Lempereur
ef8cd11a6b