Between German, English, Norwegian and Danish
I am a native speaker of German, who learned English, Latin and French at school, then Norwegian, Icelandic and Polish at University. I studied in Germany and Norway up to PhD level. My first postdoc position was in Denmark, the second was in Norway, now the third is again in Denmark. Fortunately, Norwegian and Danish are so close that they can be understood by speakers of the opposite language. As a downside, they have a tendency to infiltrate one another if you aren’t careful. This is why I have now started to attend Danish classes in order to learn Danish properly, rather than having my Norwegian becoming increasingly Danish.
At home, I speak Danish and German. At work, it is mostly Danish and English. I have given papers mostly in English, though some have been in Norwegian. My notebooks are in German, Norwegian and English depending on what I’m taking notes on. My calendar is in German, Norwegian and Danish. Publications are mostly in English, though I have some drafts in Norwegian from the time when I was employed there.
In general, I would say that my vocab in those languages is complimentary: Everything related to everyday life I would talk about in German or Norwegian (while knowing the Danish passively). Text-related and grammar-related terminology at work is mostly in German or English. My head processes palaeography and codicology in English and Norwegian. However, I will need to use a second opinion no matter which language I am writing in — even in German. And I depend a lot on Google Translate and my editor’s spell checker.
I am able to switch between languages according to whom I am talking to, but I am hardly ever aware of it. I often find myself starting a sentence in Danish and finishing it in English, or substituting single words from German. There are days when I feel pretty confident about the languages that I regularly use, and others when I feel I cannot even produce one correct sentence in either of them.