The language of science in the west is English. (I specify west because there are more Chinese-language journals in the world than English-language journals.) About 95% of the articles published in my department are written in English. The proportion of English-language conference presentations given by my colleagues is probably the same. They can go to conferences in Japan, in France, in Finland....they are in English, English, and English. You can't go into science anymore and expect a certain level of success without knowledge of English. I didn't make it this way, it just is this way. I'm not being an arrogant native English speaker. I am only describing the state of things as they are. It just happens to be lucky for me that the language of science is my native language. Imagine what would happen to scientific progress if it were carried out only in the languages of the home countries, no communication between countries, no international collaboration.
As a result, science departments and labs all across Europe, usually filled with scientists from countries on every continent, conduct their seminars in English. The works are written in English, presented at conferences in English, the scientists in the departments and labs have mixed levels of knowledge of the local languages, and it's good practice to talk about the topics in the same language in which they are written and internationally presented. There are several terms in epidemiology for which many German epidemiologists barely know the German equivalent - the English is used.
My department is an exception. We have students from all over the world - MANY from China, and also representation from other Asian and African countries, not to mention me, so we are like other science labs and departments in that regard. But we also have a strong team of documentalists who aid in research and in many cases do not need to know much English. They all know quite a lot of it, but don't need it. So when it came to vote one day before I joined the department - should our department seminars be conducted in English only like so many other places are doing? - this didn't pass my department. Seminars are conducted in either English or German, the preference of the speaker - as long as slides are in English. They let it slip if they're not.
Imagine you got here from China a week ago. You have to work really hard to bone up on your English to write those 7 articles you'll have to get out over the next two years so you can get a job after your PhD. You took a quick German class in your minuscule bit of spare time before you arrived. Now you're in a warm, crowded room with the lights dimmed listening to your department seminar - you're supposed to be grasping this stuff - and it's all in German. Yeah, you're getting sleepy.
Many students from countries where English is not the native language already have to spend inordinate amounts of time on their English to survive in science and I think we ought to cut them some slack if their German is not up to snuff. If my English was sketchy and I moved to Germany to complete a PhD in two years, you can bet I'm not going to have a lot of free time to become some kind of German expert, when I know that English can get me by long enough to get my degree.
So I just wanted to say I think people are being dicks when they make unqualified comments like "When you are in country X you have to speak X-ese." Yeah. Next time you take vacation in Slovenia, hope you've spent years getting fluent in Slovene. If you visit the Faroe Islands, hope you boned up on months and months of Faroese. If you go to a conference in Japan, hope you know Japanese.
Cut people some fucking slack.
And I think the seminars should be in English. The documentalists never have to present anyway. They are the ones who make this "you should speak German in Germany" type of comment and they are the ones who send out department-wide emails in German only and write at the end "it would be nice if someone would translate this for the non-German speakers" (yeah, it would be nice, thanks for looking into that before sending it off to some poor Hungarian who just got here a month ago and doesn't even know the word for 'fire' yet) and they are the ones who make Betriebsausflug (work field trip) plans with the intention to exclude non-German speakers from some of the activities. Get with the times - at least a third of your department is now made up of foreigners who, for at least the duration of their training, have to focus on their English to survive, and that number is increasing quickly year by year. Excluding them just means Germany pays the money to help educate them (depending on their funding source, yes) and then they feel pushed away and don't stick around.