I THINK Vladana is referring to Russenorsk, but I'm not sure it counts as a constructed language (it's a pidgin).
Also, I'm sure all the Klingon native speakers on italki list that as their native language as a joke.
@Dan Smith
Well, I think Esperanto is a bit different than this language was constructed for communication and is used for communication. But Dothraki? I can understand the appeal of different linguistic systems, but I also think that it is more exciting to learn a language that developed naturally and has a rich history and literature.
Thanks for all the comments. :-)
@ἀνάθεμα
But Nadsat isn't a fully developed language, isn't it? Isn't it more like a sociolect?
@Susanne
That's an interesting theory. I imagined more that fans of those TV series want to show off their skills at comic con. I thought it could be a way to belong to an "exclusive" group.
@Vladana
Wow, I haven't heard of the constructed North Slavi languages before. But why (and by whom) were they constructed and why are people learning them?
@Alan
Yes, I also read about the one native Klingon speaker and felt a bit sorry for the kid. I mean, Klingon is a warrior language and mainly good for offending people. The father sang the Klingon national anthem to his son as a lullaby. I wouldn't have allowed my husband to conduct such an experiment on my child. Also, there are estimates that there are only 20 to 30 people in the world who are fully fluent in Klingon, so I wondered why we have 11 Klingon native speakers on italki. Also, I read that the people who learn Klingon are not necessarily Star Trek fans.
I couldn't possibly get interested in making the effort to learn (or invent) a constructed language (conlang). However, I can understand why people might enjoy it.
As for things like Klingon, there have been groups of people who enjoy immersing themselves into "fictional universes." It's been going on at least since the early 1900s when groups of people began to form societies that enjoyed pretending that Sherlock Holmes was a real person and that the stories were nonfiction.
When college students began doing this with Tolkien, they found that Tolkien had come close to constructing some languages of his own, like Elvish, and so they tried to learn and speak Elvish. It's just part of the whole process of trying to immerse yourself in a fictional universe.
For people who are interested in the topic, you might want to know, if you don't already, that there is an Esperanto Wikipedia and it is quite well developed, with over 200,000 articles to read:
There's also Wikipedias written in Esperanto, Ido, Interlingua, Interlingue (Occidental), Lojban, Volapük and Novial.
At one time there were more or less failed projects to produced Wikipedias in Klingon and Toki Pona, but they were closed and removed. However, the Klingon Wikipedia was moved to
http://klingon.wikia.com/wiki/ghItlh%27a%27
where it still survives in some state.
I can see the interest in learning Klingon for pure linguistic fetishism - there's a very interesting talk on YouTube by the creator of Klingon, who describes how he created it to be deliberately weird and counterintuitive to make it sound as extraterrestrial as possible. As for native speakers, I've only heard of one case where a Klingon enthusiast brought up his child bilingual in English/Klingon. Apparently the child spoke it very fluently but got sick of it around age 5 when he realised nobody but his dad understood him!
On a side note, I'll never forget the frustration when I started learning Persian and discovered there more more online resources for learning Dothraki than Persian!