Or I have to learn C++ If I want to write shaders?
There is an incentive to bring bridging to c++, so there is a potential future where you will be able to write some. Although the vector of development of the language is highly depending on apple and their incentives so, unless you're willing to dig in and out the projects' github, bringing missing feature, I would say this is a yellow light. If you are ready to suffer with c++, then go ahead and learn it, but otherwise there is nothing you could do to write shaders.