ARD and ZDF, Germany's public broadcaster, publish an annual "Onlinestudie", a report on the usage of the Internet by people in Germany. Starting in 2006-ish, they have included questions on the usage of Wikipedia in their reports. https://www.ard-zdf-onlinestudie.de/
The question is not always the same and in some years, they asked people whether they use "online reference works such as wikipedia". In early years, Wiipedia was usually seen as a "Web 2.0" service or as one odd child in the social media family.
The usual (oversimplified) answer was that people in Germany use Wikipedia, especially the younger audiences.
On the methodology side, I have some reservations because I think these surveys never took into account the affirmative bias. Even at peak times, the idea of 5% of online users *actively* contributing to Wikipedia seemed far far off.
Mathias