Elvish isn't immune. A sadly lost fanfic involved a poem written in Elvish which, when translated back into English, came out containing lines like:
"Woodpeckers of globes of a flat place, I order you to die."
Many writers of anime fanfic are not fluent in Japanese. That does not stop them from using Japanese in ways that are jarringly wrong, particularly with respect to politeness levels and ways of addressing people.
The now sadly lost Star Wars fic Murder of Image was full of these, which added to its So Bad, It's Good appeal. Sample dialogue: "Out of here, you son-of-a-gun! In the Republic exist privacy, isn't it?"