In what language do scientists communicate with each other in European research institutions?
From my perspective of working in multiple European universities in different countries:
In a &quot;closed&quot; conversation setting, it will exclusively depend on the people involved in the conversation. The prime requirement is to use a language that every participant understands and speaks. A secondary concern is to use a language that people are particularly comfortable in. As a result, a meeting of two German researchers and a German student in a Swedish university will usually be held in German.
In an &quot;open&quot; conversation setting, people usually prefer to use a language that will allow other people to understand and join the conversation (usually English). Exceptions happen and might be considered as rude by some.