While the course is a licensed product, Duolingo is built upon the work of volunteers, so it took some time for them to put the Klingon course together. As they told Engadget:
On our end, it took some time to find Klingon experts who could commit the time and effort to creating a full-fledged course, as we wanted the course to be substantial and cover a lot of groundThere were also some technical issues thanks to the quirks of Klingon:
Klingon uses apostrophes in the middle of words, which is not something our system was able to handle at first, since no other language does it
Klingon also has case sensitivity, which means that a word can take on different meanings if it's capitalized or lowercased.