Experimental datapack features warning is gramattically incorrect

Actually Here be dragons is phrase that means dangerous and unexplored territories. So it is most likely intentional. You can check here about the phrase

I don't care.

Well, it's clearly referencing that, and as such the grammar is intended.

It is probably intentional. You can't just make a mistake like that. And what's with "unproffesional" stuff, Minecraft is a video-game aimed for a large audience, let them meme as much as they want.