I've been to Prague.
Younger people don't speak Russian but they understand and speak English, there is a chance that nobody would speak Russian to you in a hotel.
Many restaurants keep waitresses that understand several languages, including Russian, however menus are in English, mostly.
There are many Russian tourists accompanied by Russian-speaking guides, I'm sure you would hear Russian language everywhere.
There are practically zero information that would be written in Russian but much in English.
However if you decide to visit another city - Karlovy Vary - you would find that place very Russian-oriented: many people speak Russian, there are street signs in Russian, etc.