Haskell. I think that more people being familliar with Haskell concepts would be good for programing culture and it would increase the odds of me being able to write Haskell professionally, which is something I enjoy a lot when writing hobby code at least. Having more access to tooling and a bigger eco system would be nice as well.
I'm not a 100% sure about my answer though. For one, I might grow to resent Haskell if I had to use it at work, and there's also a risk that it would be harder to do cool innovative stuff with the language when more big companies depend on it.
Rust. I've been using it for a while, and I've been using more software written in it lately. Stuff you make with it is just better in most ways. In other languages, you have to go above and beyond to make your code fully correct, safe, user friendly, and every trait I value in software. Rust makes those things easy, and so people are more willing to do them, and so things that get made in it are better. Oftentimes it's just a matter of pulling in a crate and adding a few lines of code.
I’m obsessed with an extremely little known language called Grain. It’s not quite ready for production but it has an insanely intuitive functional syntax that I want to use noww.
I would like to see Ada grow. Its clean syntax, rich expressive capabilities, and early error detection by the compiler due to strict typing create a very pleasant experience during development. This year, the language got a new standard. Recently, a package manager and a community index were created. There's an extension/LSP for vscode, etc. Along with great educational materials on learn.adacore.com, it's easy to pick up and start using this language.
Assembly, which flavor IDK but some RISC architecture.
If everyone spoke assembly the world would be a very different experience. I'm not saying that it would be better or worse, but it'd definitely be different.
Go. I love writing go, its so simple and predictable and the accessability of multithreading and being allowed to create as many "threads" as I want make me feel smart as fuck.
It's a wonderful language, it's general purpose, it's cross platform, and it's open source (Apache license). I wish it was a mainstream language outside the of the Apple universe.
What I love the most is it's so flexible. It's a full featured OOP language, a full featured Procedural language, a full featured Functional language, a full featured declarative language, and you can relatively easily make it work with anything else you can think of.
It also has the best concurrency system I've ever seen - and with high performance computing relying so much on parallel computing these days that's a must and often what I miss the most in other languages.
A lot of other languages do some things just as well as Swift, but Swift does everything really well.
Some fun stack-based concatenative language (like Forth or Min) :3 I like playing with odd/new-to-me things that change how I have to approach things in some way. ... Also I wanna find a Forth community I can stand 😅 That or maybe a similar low-level language, I suppose. I was thinking of using it for a project but... eegh. Bleh. Et cetera. Still might, but purely on my own terms I guess.
Also, more Haskell please >:3 Or something else like it. We must spread the glory of FP nerdery @.@ ...And maybe get some more useful (and maintained) packages to work with instead of just kinda having to wonder what even builds any more v.v
Super niche, but I wish wren caught on. It's a language very similar to lua, but indexes start at 0. Also it has some cool features too, but mostly the index thing.
I've heard of one I don't know the name of that is trying to make it so you can just write the program with natural English kind of like how AI works off of prompts. Having grown up watching Star Trek and seeing how they would "write" holodeck programs by just giving the computer a detailed explanation of the program they wanted to run always made me wish we could do that IRL.