We do not sell or share personal account information with third parties.
When you create a Duolingo account, you choose a username and provide us with an email address, which is not public. The username/name you chose can be seen by other users of Duolingo. Please note that your friends can find you via the search function if they know which email address you used for your account.
Be aware that if you are a student or teacher using Duolingo for Schools, your email can be seen by your teacher (and students can see the teacher's email).
Note: if you are a parent or a teacher, you can learn more about student privacy via Duolingo for Schools. Here is how.