Most Arabic and Chinese speakers are not Catholic either.

The Vatican has shown a persistent interest in Russia, and yes, there is a significant Russian speaking Catholic minority, as well as a potential convert base. If I remember rightly, Russia (or the USSR) gets a prominent mention in the Fatima narrative.

Russian has declined a lot in importance over the past thirty years, but it is still a major world language in terms of its spread. It is a surprising omission.