I'll echo the rest of the people's comment and say Python. It's reasonably easy to pick up, and is really versatile. I personally use it for some backend work, and it's a joy to use. One language that I am intrigued by is C# and dotnet. I live in the Midwest, and there are way more dotnet jobs than there are Python, which surprised me at first, but then I figured most of the shops here would have been on prem installations. The tooling from Microsoft has improved a lot in the past 3 year. I myself will be looking at C# just to see how it feels to use.