The thing you’re describing definitely happens. Just did a quick check with Steam in German and every game had a few reviews in English (just checking the preview of Most Helpful and Most Recent at the bottom of the store page). Other languages are more affected, like Swedish, where most of the reviews are in English.

I don’t really see a good solution to this. If Steam is able to correctly detect the language and only show your native one, most of the time you’ll probably end up with a handful of reviews, and then Steam has to show you something else (probably English) anyway. I think currently it’s good enough, since you still get the perspective of someone from (probably) your regional or cultural background, even if the language might not fit.