Whatever you are most comfortable with language wise. Anything is perfectly capable of these tasks, it's just simple byte manipulation.

The big thing you will need to decide is what to use for your CAN interface.

The two big options are to use the J2534 DLL API, where there are lots of commercial devices available like OpenPort, Panda or commercial devices like DrewTech - but you're stuck to Windows only besides some major hacks. This will work from any language that can load a shared library, so Python, C#, C, C++, node.js, Java, pretty much anything will work.

Or to use SocketCAN, which is very strictly Linux only but is like "normal" sockets programming, so could be easier if you are familiar with this. Again, pretty much any language on Linux can use sockets, so all good here. Panda also works as a SocketCAN device, or you can build a full small Linux computer to use with something like a Raspberry Pi and a Seeed Studios CAN hat, or a Macchina P1.

Then there are a bunch more obscure options too, like to use Python-CAN with or without SocketCAN, or the million different one-off CAN platforms (Vector, Kvaser, blah blah).

Overall, I would pick the language you are most comfortable with, then pick a device that will work with that language on the platform you would like to use, then get to work. I write most of my tools in Python using python-can just because it was simple to get started and is cross-platform, but there's no reason I couldn't have written them nearly as quickly in C#, TypeScript, or even Pascal if I had wanted.

If you want to work on windows, use C# and J2534.
C# has full primitives, which is very useful, as well as the ease of using a garbage collected language, with the ability to easily link into native code via C++ interop. I would dare say, it is in a very unique and privileged place in the Windows ecosystem.
If you ever need to do something resource intensive, then the ability to have good interactive profiling tools and easy native access to the OS comes in handy.

Whatever you do won't be cross platform anyway, since Linux and Windows have totally different ways of interfacing with the hardware, so you need some sort of abstraction layer.

So your first question is what do you want to do.
If you want to build a dedicated middleware device on something like a raspberry pi or ESP32, then Python is a very good choice.
If you want to make something that uses available J2534 hardware from a PC, then I'd say C# (or Visual C++) is your only good choice, everything else will have a lot of pain to get working.

I am not going to go into philosophical debates about Windows vs Linux and open vs closed standards, I am just speaking from a purely practical point of view.

For windows, C# is the most obvious solution.