All VRMMO's have language settings. 

So it doesn't matter what language you speak. 

It will all be understood by others as whatever preferred language they set. 

Also the language that humans speak, in this world, is just called the Common Language, which some non-human humanoid creatures are capable of speaking/understanding basic versions of. 

And yep, you are correct. These enemies are not just basic mooks, they all have intelligence of some kind and can adjust their strategies accordingly based upon what they are capable of. Its much more real world than most VRMMOs where attack patterns can become predictable.