How to get active locale (language) of the page, from where visitor submit booking?

On the Booking Listing page exist ability to change language (locale) of emails, that will send to visitor during approving or declining of the booking. But how to detect language/locale of webpage, from where visitor submit the booking.
Here is instruction how to do this.
Please open the Booking > Settings > Fields page and add to the booking form this shortcode and JavaScript code:

<div style="display:none;"> Active Language: [text active_language class:wpbc_lang_field]</div>
<script type="text/javascript">
    jQuery('.wpbc_lang_field').val( wpbc_active_locale );

Its will add to your booking form new field [active_language] and JavaScript for auto-inserting active locale into this field. Please note, this field is not visible for visitors, because of this CSS: style="display:none;"

Also you will be need to add to the "Content of booking fields data" form (its at the bottom of Booking > Settings > Fields page) this shortcode:

<strong>Active Language</strong>:<span class="fieldvalue">[active_language]</span>

For showing this field at the Booking Listing page.