"I speak a language."
Are you asking why this sentence uses vI- instead of jI-?
Many languages only conjugate the verb based on the subject, English included. However, Klingon includes both the subject and the object in the prefix. jI- does not mean "I do something", it means "I do something, but not too anyone or anything specific" (first person singular subject, no object) - I don't speak anything in particular, I speak in general. But in this sentence there IS an object. The thing I am speaking is "a language". So I have to use the prefix that means "I do something to something or someone else" (first person singular subject, third person object): vI-.
Have you read the Tips & Notes for this unit? Since Duolingo has hidden the Tips & Notes I want to make sure you know about them and where to find them. If you have not been reading the Tips & Notes, I would like to ask that you review those so we don’t have to repeat too much of the information that we have explained there.
If you are doing the course on iOS or Android, you cannot currently access the Tips & Notes through the app. To access the Tips & Notes, you will have to access the course using a web browser at https://www.duolingo.com/. You can still do it on your mobile device, but you will have to use the web browser instead of the app (or you can do it from a computer). When you click on a Skill, it will expand to reveal a large Start button, a small key button, and either a large Tips button or a small light bulb button. The lightbulb is shown in the picture below.
If you click on the Tips button or the light bulb it will reveal the Tips & Notes and give you a detailed explanation of the grammar that is introduced in that Skill. If you have questions after reading the Tips & Notes for any Skills, then please return to the forum to ask your question, explaining what you didn’t understand or what seems contradictory to you.