Hi,
The datepicker should follow the wordpress locale automatically, as it is a built in WordPress script, our plugin is only using it from WordPress core. Make sure that the locale is set correctly on your back-end. WordPress will automatically enqueue the translations.
The font should be inherent, but if for some reason it’s overridden by any 3rd party css, then try this custom CSS to force the font you want:
.asp-ui.ui-widget {
font-family: 'Open Sans' !important;
}