I think in the application if you say I want to study x and y they will think about whether you are qualified to study x and y at their university. And also whether they have x and y.
Also realistically it would be silly to be overly committed to particular majors before you even set foot on a college campus. I don’t think that means you should avoid mentioning what areas you’re interested in, but make sure you will stack up favorably for doing what you are interested in, and show how that institution fits in with those interests.
This might be interesting to you regarding Cornell admissions.
http://www.news.cornell.edu/stories/2014/12/arts-and-sciences-reading-every-admission-application
In order for you to ultimately decide it is really the best place for you, somehow you must conclude that what they will offer in the way of Russian will really suffice. In which case it might be wise to address that in your essay, lest they otherwise get the impression from elsewhere in your application that you might prefer someplace that had more to offer than they can provide.
Keep looking though. You may well find some other schools that you like at least as well otherwise but offer more in the way of Russian.