I'd start with Sonic Pi and see how you go. It's a small but useful subset of the bigger and more complex apps. If you want to take it further you can move up to SuperCollider, because the syntax is similar.
sc is probably the biggest and most open and developed sound language. pd is in the same ballpark, with a different culture.
It's also worth learning web audio, because then you can build toys for the web.
The others are more niche. I'd written off Csound, but I discovered recently that some of the newest Csound music has better than usual production values, which makes me wonder if it's having a revival and breaking out of the academic ghetto these projects tend to get trapped in.
sc is probably the biggest and most open and developed sound language. pd is in the same ballpark, with a different culture.
It's also worth learning web audio, because then you can build toys for the web.
The others are more niche. I'd written off Csound, but I discovered recently that some of the newest Csound music has better than usual production values, which makes me wonder if it's having a revival and breaking out of the academic ghetto these projects tend to get trapped in.