Populate a input field with selected checkboxes

IN PROGRESS
Bids
16
Avg Bid (CAD)
$39
Project Budget (CAD)
$30 - $250

Project Description:
I have a website with a form.
You can see it here:
http://www.abcd1234.ca/fr/template_listing_intervenants.php
(Idées de séjour in the header)
There is 2 text input field (idees_sejour_selection1 and idees_sejour_selection2)
If you click the grey arrow image, a drop-down menu open.
In these drop-down, there is checkboxes.
When you check checkboxes and you click "Confirmer" button, I want the corresponding input text field to be fill with text form selected checkboxes of the drop-down menu.
The text must be pulled form the tag of the label of the checkboxes.
Each text entry must be separated by a comma (,)
These input text fields are just visuals indicator: their are not use for the search filter.
The script must be versatile if we add checkboxes in the future.

You can see a live example here:
http://tourisme-megantic.com/accueil.php?lang=en
In the "Suggested area" section.

Skills required:
Javascript, jQuery / Prototype
About the employer:
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