I've noticed that some of the American astronauts on the ISS can speak (at least a smattering of) Russian and similarly, some of the Russian cosmonauts are fluent in English. Is such bilinguality a requirement for all/some of the occupants of the ISS? If not, how do the two parties communicate?
From the NASA Astronaut Candidate Program brochure:
Applicants should be aware that selection as an Graduation from the Astronaut Candidate Program will require successful completion of the following: International Space Station systems training, Extravehicular Activity skills training, Robotics skills training, Russian language training , and aircraft flight readiness training.
From JAXA's website:
After being selected, astronaut candidates undergo Basic Training. They obtain basic knowledge and technical skills in space engineering, space science, space medicine, the Space Shuttle and ISS systems, the English and Russian languages. They also receive flight training and physical training. Upon completion of Basic Training, they are officially certified as astronauts …
From the Russian Cosmonaut Training Center's Candidate Selection Criteria:
... знания русского языка (письменно и устно) должны быть не ниже хороших, относительно требований средней школы Российской Федерации; знания английского языка на оценку не ниже «хорошо» по требованиям вузов Российской Федерации;
Russian language skills (written and oral) must not be less than good, according to the requirements of high school in Russian Federation; the knowledge of the English language assessment at least good according to the requirements of higher education institutions of the Russian Federation