If you want to go into space and to become an astronaut with NASA, then you are advised to go ahead and start polishing up your Russian. The reason for that is quite simple. You must be able to have a conversation in Russian, and be pretty fluent, before you are ever going to be allowed to get to the International Space Station.

All NASA is doing is being extra cautious. Because even though all nationalities share the space station, there are certain parts that are classed as being the Russian part and other parts are the United States section. Speaking Russian is then required just in case something goes wrong near the Russian part and you are required to speak to Russian command in order to resolve the problem.

See, it does all make sense in the end.