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)
What is „my language“? Because depending on where the game is from this changes. Have they thought of that? Because I know from experience that US companies cannot comprehend speaking more than one language.