Echo directories and load images dynamically for an image gallery

Echo directories and load images dynamically for an image gallery

Please forgive me if I'm posting on the wrong forum for this is my first post here.
I designed a portfolio for a client in which she can display her work. Most of my clients are looking for easy editable portfolios. So I decided to use a combination of the galleria plugin and CMS editing.
The gallery is working fine and everything was doing ok until she told me she needed several galleries inside her portfolio.
So when she wanted to make a new gallery collection, she would have to create a new file, mess up styling it and then mess up with the nav bar adding the link. So I thought there must be a way of doing this with AJAX.
Maybe if she puts her images on a folder and then she names that collection in a file inside that folder (to use in the nav link), and every image inside that folder could be loaded dynamically inside the <ul id="galleria"><li><img src="#" /></li></ul> in the #mainContent.
I'm not really much of a programmer, most of my work is design and simple HTML/CSS/PHP. I'm not a jQuery/JavaScript guru like you guys ;)
Could you please help me? Is this posible?

Please take a look at the following code. I've compressed the whole site code if you'd like to see it in the browser.
The JS is stored in /scripts/init.js
The nav bar is /en/includes/menu.php
The images should load in <ul id="galleria"> in en/portfolio.php

I did not include the fonts folder for obvious copyright reasons, so the site won't display visually as intended. also I did not include the images because of the size. In case you chose to view the site in your browser you'll need a tool like MAMP, or if you prefer I'll upload the site and give you the link.

Thank you very very much! Any help is appreciated. :D