Note that the metric here is "is the tweet in one of the languages spoken by the user". This hypothetically allows more nuanced implementations than you contemp

Note that the metric here is "is the tweet in one of the languages spoken by the user". This hypothetically allows more nuanced implementations than you contemplate. For example, they could have a language "unrecognized" and assume everyone speaks it. I broadly find this useful: I see tweets in other languages when they're retweeted by people I follow, and about half the time I machine translate them. But I don't want my whole feed to be that.