"I do not speak Federation Standard."
Translation:DIvI' Hol vIjatlhbe'.
Yes, that's correct.
In the font used in the website, the small L has a little curl at the bottom while the capital i is completely straight.
I'm not sure what it looks like on the mobile apps but hopefully they also let you distinguish between the two letters somehow.
There are descriptions of how to pronounce the various letters in Klingon in the tips and notes for the "Sounds 1" unit -- as soon as you have done it, the following URL should work for you: https://www.duolingo.com/skill/kl/Pronunciation-1/tips-and-notes
One thing to watch out for is that tlh is considered a single letter in Klingon.
I wonder if you are correctly typing the different I and l letters. That is often the cause of that type of problem. Please look carefully (within the Duolingo system - you may not be able to see it if you're reading this in an email). The l (lower case L) has a small curl at the bottom and the I (upper case i) does not have the curl. The sentence in this exercise contains a combination of l and I characters and you must type the correct letters to get it right. Can you see the difference? Do you think that might have been the problem?
Have you been reading the tips and notes which explain the grammar of English?
Tips and notes are not available (for most users) on the mobile apps, so if you are using a mobile app to learn Klingon, I would recommend that you switch to using the website https://www.duolingo.com/ instead.
On the website, after you choose a unit, click on the lightbulb next to the "Start" button in order to see the tips and notes:
The lightbulb icon may not appear if you are viewing the website on a small screen (e.g. a smartphone); you may have to use a tablet, laptop, or other bigger screen to get the tips and notes.
If, after reading the tips and notes, you still have questions or something is confusing or contradictory in them, feel free to ask specific questions.