There is no best language for writing malware you can use any computer programming language to write malware. But most malware coder go with compile language such as C/C++ golang, C# and more but malware can also be written in scripting language like python, ruby and JavaScript infact lots of malware as been written in those scripting language expecially python, if you used to read thehackernews.com blog you will understand what I’m saying, there was a malware attack this year was written in python.
The reason malware coder go with compile language is because of spead, size and easy to package compared to scripting language which is slow and big file size. So For me I will say you should go with C and Golang, because lots of security expert are making use a Golang recently to do all kinds of security jobs and lots of malware coder have started making use of it also to attack network.
You can combine both C and Golang.
It’s depends on what your malware wanna do
With that two you are good to go.