[Javascript, PHP and, I think, AJAX], panicking a little bit about my dissertation project

Basically, I'm pants at Javascript, PHP and AJAX. The only experience I have with AJAX is memorising a jQuery + AJAX script to make the background of a Dr. Who website alternate from blue and black. However this is my situation:

I have to create an app for my project which requires me to create an instant messenger that translates between Polish and English, so I can invite participants into a room and they'll all use the app; create an account and communicate to one-another. It's a language experiment for my dissertation. However as I said, I don't know much about Javascript and PHP, so I don't know where to start in terms of creating a registration system and log-in screen. And I have no idea where to start with creating an instant messenger with Javascript.

They will select from a limited number of messages, like common phrases, and they will select an emoji to send it with, to which the message and emoji will be sent as a message. And when they reply, the translation to their language will appear.

Anyway can someone help me out? I'm worrying a little bit.

Edit: Oh yeah, I designed what I want it to look like, to help give an idea.. https://www.dropbox.com/s/3b9e1r4612eqjq2/completedflowchart.psd?dl=0

Edit2: Thank you for the replies and advice guys. I'll try and learn the technologies you recommended. As for that one guy who down-voted: I hate you.