What do you think about people who learn fictional languages like Quenya and Klingon?

I think it's cool. Back in school days, my group of friends invented a sign language that we only used among ourselves. I personally don't have any motivation to do it, but there used to be (or still is) a group of Avatar fans that learned the Na'vi language, but it never became as popular as Klingon. It's a way to turn fiction into reality.

If it tickles their fancy more power them.

It's a hobby that will stretch their minds and help them to learn real languages.

Stupid as there aren't any native speakers to speak to.

Klaatu barada nikto

Intelligent teenagers looking for a way to occupy their active minds, but finding video games boring.

I truly hope those aren't their only foreign languages. Even Esperanto is far more useful.

If that's the say they choose to spend their time, it's okay with me.

I think they've got a hobby

Dedicated movie buffs.