"I speak Klingon."
Translation:tlhIngan Hol vIjatlh.
I've gotten a lot of sentences throughout lesson one that have said I made a typo when I didn't - everything down to the punctuation was the same. For example, on this sentence, it said that I made a typo on vljatlh. I don't know if that's something that the contributors have any power over or if Duo needs to fix it, and it's still counted them as correct and let me move on - but wanted to let you know.
Unfortunately Duolingo uses a font which makes it difficult to see the difference between an l (lower case L) and an I (upper case i). If you look carefully, you can see that the lower case L has a small curl at the bottom that is missing from the bottom of the capital i. Compare the l where you have typed the sentence to the I in the translation given by the software. I suspect you will find that all of thoss rejections when you thought you were right, have an l substituted where an I should go.