HTML, JavaScript, and CSS are going to be required for any front-end, content, and design work.
As for back-end (if needed)...kinda depends. I'm a .NET Developer, so I work with C# as a back-end language; others may work in Python, PHP, or even just stick with JavaScript and run a Node.js application.
If your website needs a database, then there's traditional SQL such as Microsoft SQL and MySQL (both are standard SQL syntax). There's also NoSQL databases storage such as MongoDB, ElasticSearch, etc.