What language should I learn to pull information from a third party site in real time

I want to develop a website that pulls information from a particular third party site in real time. I want to select certain products from this website, post them on my own site, but want the user to be able to filter through the products based on the current information provided from the third party site (i.e. brand, size, availability) I know HTML, CSS and Javascript but unsure on which backend language I would need to learn to develop this function. Any help would be greatly appreciated!