What’s the most suitable programming language for AI development?
Disclaimer: this is massively subjective topic, and below is just my opinion.

I would say it depends on your focus. You could do work in these areas with any major programming language, but some have better suited capabilities and/or better support from a community.
My biased and very simple answer would be to use Python for basically everything, and learn C++ for times when performance is important. And then, if you get really serious, you'll need to learn CUDA (extensions to C++ to programme directly for Nvidia GPUs). If you are proficient at Python and C++, there isn't really anything you couldn't do.
In summary

If you want to do research, you could probably do everything with just Python. There are libraries such a NumPy/PyTorch/Tensorflow which do all the heavy lifting for you.

If you want to go the way of robotics and embedded hardware/software, you'll likely need C/C++.

If you want to make models to deploy in a browser, perhaps Javascript would be useful.