We have a dashboard for tracking notifications sent by the TheWikipediaLibrary extension, notifying users that they qualify to receive access to The Wikipedia Library. Although we got feedback from users on this wording when initially deploying it, we never did any A/B testing of different messaging.
On ro.wiki, @Strainu would like to test some different messages for this notification, to see if they impact clickthrough rates. This can be done by volunteers by updating/overriding translation strings. We don't measure clickthrough rates, but we do measure what % of sent notifications are marked as read, which is probably a good enough proxy.
We have an internal Superset dashboard which tracks this data, but it's only configured to track data from English Wikipedia.
If we added Romanian Wikipedia, we could help Strainu with this experiment and share data from this dashboard.