https://meta.wikimedia.org/wiki/Research:Study_of_performance_perception_on_Wikimedia_projects
The study has progressed a lot in recent months, there's a (currently embargoed) research paper that came out of it. As a follow-up we've identified the need to collect more data, in order to attempt using deep learning (neural networks) to make a better prediction of user opinion about page performance.
Spanish Wikipedia is particularly interesting because it gets traffic from very diverse countries, and it's a high traffic wiki.
The format of the survey hasn't changed since T188503: Identify two wikis to run a research study and get approval from their respective communities