What programming language do I need to learn to build a trade by barter app?

Users of the app will be able to:

1. Upload their products they will like to trade for other goods.

2. See the top products.

3. Enter the amount or particular product/item they will like to exchange for.

4. Search for product/item.

5. Create a profile/account.

6. Chat with each other.

Summary: the whole idea of the app is to reintroduce the outdated trade by barter mode of exchange.

*I know a bit of HTML, CSS, and JavaScript