I have in the past experiemented with LWJGL2, however with my most recent game I am using LWJGL3.
I am looking more into writing shaders for normal mapping and other fun stuff.

As far as I know OpenGl's Shader Language is the main shading language used with LWJGL. Are there other shader languages that can be used with LWJGL3? What are they? What are the benefits of them?

LWJGL is a warpper library for OpenGL. So there are no other graphics APIs available.
And since there is only one shading language for OpenGL (GLSL), you can only use that language.
If you want to use another shading language you have to use another graphics API.

But OpenGL has all the functionality for doing normal mapping and other stuff with the providede shader API.
I don't know if there are benefits for using Direct3D and the HLSL shaders but performance reasons on windows.