The number of readers and authors on the Wikipedia has been declining for years. This has various causes, some of which can no longer be solved or cannot be solved in a short term. The Wikipedias have a large number of encyclopedic articles, which can on the one hand only be expanded with great effort, but do not cover all needs on the other hand. In addition, the Wikipedias are confronted with sometimes considerable social problems.
Increased use of the sister content projects like Wikibooks, Wikivoyage, and Wikinews could help alleviating some of these issues. On the one hand, these wikis provide important factual information that encyclopedias cannot provide by definition, and can therefore increase the attractiveness of the entire Wikimedia universe. However, these wikis should be made much more popular.
On the other hand, these wikis are ideal for training new authors. They use the same Mediawiki software and similar templates and tools. Authors can more easily create articles even with less extensive knowledge. The rules are simpler, and there are more helpful sample. Authors can feel freer in a more relaxed environment and community, and they can make mistakes without being drawn into extensive or defamatory discussions. Ultimately, they are well prepared to work on other Mediawiki projects, too.

Session recording: https://youtu.be/XOeZ8sHimN0?list=PLhV3K_DS5YfJdC5P86rsDsUtxEow0gDnR&t=6500