It was held yesterday in my hometown. Unfortunately i didn't know about this so i didn't see it.
Enyways, here is the article from one of our news portals, which contains some pictures:
http://www.index.hr/xmag/clanak/u-rijeci-premijerno-prikazana-prva-klingonska-opera-na-svijetu/601154.aspx
Translation:
The first ever klingon opera has premiered yesterday in city of Rijeka, Croatia, at one of towns theatres. It was preformed by Zeebelt theatre from Netherlands. This was a treat for all "Star Trek" fans, science fiction fans in general, and all who are just curious.
Opera under the name "U" is preformed in the fictive language of the Klingons, a warrior race from popular SF series "Star Trek". Marc Okrand, who is a leading expert in klingon language, assisted with the production of the opera and its performance in klingon language.
Today, all over the world, there are around 5 million people that speak this artificial language, which possesses it's own writing and grammar. Current trend with this language is translating of famous literature including the most famous of books, the Bible.
(I think i translated it well)