It looks like we don't have the translated page you're looking for, but we do have other content in English and offer support in English.
All users (including collaborators) can follow tasks, regular users can add any other user as a follower, and external users can make someone a follower if that task is already shared with that person.
Following a task allows you to keep track of its progress. You'll see all the changes made in the global Stream as well as receive notifications to your email.
When you're assigned to a task or someone shared a task with you, you're automatically added as a follower to this task.
If you want to add yourself (or your teammate) as a follower:
Open a task in Task view.
Click the following icon on the panel above the description field.
Click +.
Search for the user you want to add as a follower and select them from the list.
To add yourself, click Follow task.
When you unfollow a task, you stop receiving all updates about the task, but you'll be able to see these updates in the task stream. Also, you can delete followers from tasks, so people with whom the task is shared stop receiving notifications as well.
Open a task in Task view.
Click the following icon on the panel above the description field.
Click Unfollow task if you want to unfollow.
Or hover over the person you want to delete from followers and click the X that appears.
You won't be able to stop following a task if you're assigned to it. If you stop following a task you won't automatically stop following its subtasks, but you can repeat the above process for any subtasks you no longer want to follow.