What programming language is used for online projects like jibjab.com?

Question

Programming languages

I make videos in Affter Effects and Premier Pro. I would like to try to make an online project, where the user himself added text and photos to the created video templates.

In what programming language, technology, libraries are online projects like this https://www.jibjab.com made ?

PS I have only experience in creating websites and I don’t understand in which direction to look for an answer to the question. It would be a shame to start learning, for example, Python, and later find out that it is poorly suited for this task and you need to do it in another programming language.