I've been unemployed for 3 years and feel like I've lost my knowledge about website backend development because I don't keep up with advances in that field. Now that I want to dive back into that world, what programming languages do I need to learn to get a job quickly?

The fact of being alive compensated for what life did to one.

If I were you I would do the following 

- look into freecodecamp
Quickly dive through the content and make those projects 

- work on some app , could be anything for ex full stack clone of the todoist app with all features 

- look into interview prep blogs and content

- mock interviews (to test waters)

Software engineer | history buff | 3x startup early employee

I never knew if sites like freecodecamp existed. I really appreciate your suggestions. Will check and try in a few months

I heard good things off project Odin too:

I heard good things off project Odin too: https://www.theodinproject.com/

product/design/UX exploring web3 🌐 nf.td/mario — ~sigmes-modfyn

New reference for me. I will check it now. Thanks!