IMHO foreign language skills are very important for fellowships in Europe.
Surely your colleagues can adapt and speak English in order to explain a couple of things, but the entire clinic cannot switch its language to English for one fellow. Not everyone (outside most physicians) speaks or understands English well enough to be able to work using it only.
And in radiation oncology we have to interact with a lot of people: dosimetrists, therapisits, physicists.
Furthermore, if you can't speak the local language you are basically screwed, when it comes to talking with patients, attending tumor boards, etc.
In surgical specialities this is not that much of an issue, since most of what a fellow is supposed to learn/offer happens in the OR. There, the small team of 1-2 surgeons can switch to English and the patient is asleep anyway.
I remember meeting a couple of Japanese fellows during my rotation in surgery 5 years ago as a med student, they were basicall in the OR the whole day.