I know I’m late to the party but I just found out and didn’t find a post regarding this
TL;DR: Steam now calculates review scores based on reviews made on your languages only (if enough). This is on by default, but can be reverted to go back to review scores based on all reviews (from people that purchased the game directly on Steam only)
Isn’t this already the case?
Unless there’s a setting I missed, right now you can only change both settings at the same time.
Oops, my bad then, I didn’t test the feature yet, only read the blog post and thought “off topic” reviews didn’t change